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| number = ML16204A008 | | number = ML16204A008 | ||
| issue date = 05/31/2016 | | issue date = 05/31/2016 | ||
| title = | | title = Redacted Version of Revision 29 to Updated Safety Analysis Report, Chapter 15.0 - Accident Analysis | ||
| author name = | | author name = | ||
| author affiliation = Wolf Creek Nuclear Operating Corp | | author affiliation = Wolf Creek Nuclear Operating Corp | ||
Latest revision as of 22:23, 2 April 2019
| ML16204A008 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 05/31/2016 |
| From: | Wolf Creek |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML16203A351 | List:
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| References | |
| WM 16-0008 | |
| Download: ML16204A008 (569) | |
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{{#Wiki_filter:WOLF CREEK TABLE OF CONTENTS CHAPTER 15.0 ACCIDENT ANALYSIS
Section Title Page
15.0 ACCIDENT ANALYSIS 15.0-1
15.0.1 CLASSIFICATION OF PLANT CONDITIONS 15.0-1
15.0.1.1 Condition I - Normal Operation and 15.0-1
Operational Transients
15.0.1.2 Condition II - Faults of Moderate Frequency 15.0-3
15.0.1.3 Condition III - Infrequent Faults 15.0-4
15.0.1.4 Condition IV - Limiting Faults 15.0-5
15.0.2 OPTIMIZATION OF CONTROL SYSTEMS 15.0-6
15.0.3 PLANT CHARACTERISTICS AND INITIAL CONDITIONS 15.0-6
ASSUMED IN THE ACCIDENT ANALYSES
15.0.3.1 Design Plant Conditions 15.0-6
15.0.3.2 Initial Conditions 15.0-7
15.0.3.3 Power Distribution 15.0-8
15.0.4 REACTIVITY COEFFICIENTS ASSUMED IN THE 15.0-9
ACCIDENT ANALYSES
15.0.5 ROD CLUSTER CONTROL ASSEMBLY INSERTION 15.0-9
CHARACTERISTICS
15.0.6 TRIP POINTS AND TIME DELAYS TO TRIP 15.0-10
ASSUMED IN ACCIDENT ANALYSES
15.0.7 INSTRUMENTATION DRIFT AND CALORIMETRIC 15.0-11
ERRORS - POWER RANGE NEUTRON FLUX
15.0.8 PLANT SYSTEMS AND COMPONENTS AVAILABLE 15.0-12 FOR MITIGATION OF ACCIDENT EFFECTS
15.0.9 FISSION PRODUCT INVENTORIES 15.0-12
15.0.9.1 Activities in the Core 15.0-12
15.0.9.2 Activities in the Fuel Pellet Clad Gap 15.0-12
15.0.10 RESIDUAL DECAY HEAT 15.0-13
15.0.10.1 Total Residual Heat 15.0-13
15.0.10.2 Distribution of Decay Heat Following 15.0-13
Loss-of-Coolant Accident
15.0.11 COMPUTER CODES UTILIZED 15.0-13
15.0.11.1 FACTRAN 15.0-14
15.0.11.2 LOFTRAN 15.0-14
15.0.11.3 PARAGON/NEXUS 15.0-15
15.0-i Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
Section Title Page
15.0.11.4 ANC 15.0-15
15.0.11.5 TWINKLE 15.0-15
15.0.11.6 APOLLO 15.0-16 15.0.11.7 RETRAN-02 15.0-16
15.0.11.8 VIPRE-01 15.0-16
15.0.12 LIMITING SINGLE FAILURES 15.0-16
15.0.13 OPERATOR ACTIONS 15.0-17
15.0.14 REFERENCES 15.0-19
15.1 INCREASE IN HEAT REMOVAL BY THE SECONDARY 15.1-1 SYSTEM
15.1.1 FEEDWATER SYSTEM MALFUNCTIONS THAT RESULT 15.1-1
IN A DECREASE IN FEEDWATER TEMPERATURE
15.1.1.1 Identification of Causes and Accident 15.1-1
Description
15.1.1.2 Analysis of Effects and Consequences 15.1-2
15.1.1.3 Conclusions 15.1-3
15.1.2 FEEDWATER SYSTEM MALFUNCTIONS THAT RESULT 15.1-3
IN AN INCREASE IN FEEDWATER FLOW
15.1.2.1 Identification of Causes and Accident 15.1-3
Description
15.1.2.2 Analysis of Effects and Consequences 15.1-4
15.1.2.3 Conclusions 15.1-6
15.1.3 EXCESSIVE INCREASE IN SECONDARY STEAM FLOW 15.1-7
15.1.3.1 Identification of Causes and Accident 15.1-7
Description
15.1.3.2 Analysis of Effects and Consequences 15.1-7
15.1.3.3 Conclusions 15.1-9
15.1.4 INADVERTENT OPENING OF A STEAM GENERATOR 15.1-10
ATMOSPHERIC RELIEF OR SAFETY VALVE
15.1.4.1 Identification of Causes and Accident 15.1-10
Description
15.1.4.2 Analysis of Effects and Consequences 15.1-11
15.1.4.3 Conclusions 15.1-13
15.0-ii Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
Section Title Page
15.1.5 STEAM SYSTEM PIPING FAILURE 15.1-13
15.1.5.1 Identification of Causes and Accident 15.1-13
Description
15.1.5.2 Analysis of Effects and Consequences 15.1-16
15.1.5.3 Radiological Consequences 15.1-21
15.1.5.4 Conclusions 15.1-25
15.1.5.5 Notes 15.1-25
15.
1.6 REFERENCES
15.1-26
15.2 DECREASE IN HEAT REMOVAL BY THE SECONDARY 15.2-1 SYSTEM
15.2.1 STEAM PRESSURE REGULATOR MALFUNCTION OR 15.2-1
FAILURE THAT RESULTS IN DECREASING
STEAM FLOW
15.2.2 LOSS OF EXTERNAL ELECTRICAL LOAD 15.2-2
15.2.2.1 Identification of Causes and Accident 15.2-2
Description
15.2.2.2 Analysis of Effects and Consequences 15.2-4
15.2.2.3 Conclusions 15.2-4
15.2.3 TURBINE TRIP 15.2-4
15.2.3.1 Identification of Causes and Accident 15.2-4
Description
15.2.3.2 Analysis of Effects and Consequences 15.2-5
15.2.3.3 Conclusions 15.2-9
15.2.4 INADVERTENT CLOSURE OF MAIN STEAM 15.2-10
ISOLATION VALVES
15.2.5 LOSS OF CONDENSER VACUUM AND OTHER EVENTS 15.2-10
RESULTING IN TURBINE TRIP
15.2.6 LOSS OF NONEMERGENCY AC POWER TO THE 15.2-10
STATION AUXILIARIES
15.2.6.1 Identification of Causes and Accident 15.2-10
Description
15.2.6.2 Analysis of Effects and Consequences 15.2-12
15.2.6.3 Radiological Consequences 15.2-14
15.2.6.4 Conclusions 15.2-16
15.2.7 LOSS OF NORMAL FEEDWATER FLOW 15.2-17
15.2.7.1 Identification of Causes and Accident 15.2-17
Description
15.2.7.2 Analysis of Effects and Consequences 15.2-18
15.2.7.3 Conclusions 15.2-20
15.0-iii Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
Section Title Page 15.2.8 FEEDWATER SYSTEM PIPE BREAK 15.2-20
15.2.8.1 Identification of Causes and Accident 15.2-20
Description
15.2.8.2 Analysis of Effects and Consequences 15.2-22
15.2.8.3 Conclusions 15.2-26
15.
2.9 REFERENCES
15.2-26
15.3 DECREASE IN REACTOR COOLANT SYSTEM FLOW 15.3-1 RATE
15.3.1 PARTIAL LOSS OF FORCED REACTOR COOLANT FLOW 15.3-1
15.3.1.1 Identification of Causes and Accident 15.3-1
Description
15.3.1.2 Analysis of Effects and Consequences 15.3-2
15.3.1.3 Conclusions 15.3-4
15.3.2 COMPLETE LOSS OF FORCED REACTOR COOLANT 15.3-4
FLOW
15.3.2.1 Identification of Causes and Accident 15.3-4
Description
15.3.2.2 Analysis of Effects and Consequences 15.3-5
15.3.2.3 Conclusions 15.3-6
15.3.3 REACTOR COOLANT PUMP SHAFT SEIZURE 15.3-6
(LOCKED ROTOR)
15.3.3.1 Identification of Causes and Accident 15.3-6
Description
15.3.3.2 Analysis of Effects and Consequences 15.3-7
15.3.3.3 Radiological Consequences 15.3-11
15.3.3.4 Conclusions 15.3-15
15.3.4 REACTOR COOLANT PUMP SHAFT BREAK 15.3-15
15.3.4.1 Identification of Causes and Accident 15.3-15
Description
15.3.4.2 Conclusions 15.3-16
15.
3.5 REFERENCES
15.3-16
15.4 REACTIVITY AND POWER DISTRIBUTION ANOMALIES 15.4-1
15.4.1 UNCONTROLLED ROD CLUSTER CONTROL ASSEMBLY 15.4-2
BANK WITHDRAWAL FROM A SUBCRITICAL OR
LOW POWER STARTUP CONDITION
15.4.1.1 Identification of Causes and Accident 15.4-2
Description
15.4.1.2 Analysis of Effects and Consequences 15.4-4
15.4.1.3 Conclusions 15.4-6
15.4.2 UNCONTROLLED ROD CLUSTER CONTROL ASSEMBLY 15.4-7
BANK WITHDRAWAL AT POWER
15.4.2.1 Identification of Causes and Accident 15.4-7
Description
15.0-iv Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
Section Title Page
15.4.2.2 Analysis of Effects and Consequences 15.4-8
15.4.2.3 Conclusions 15.4-12
15.4.3 ROD CLUSTER CONTROL ASSEMBLY MISOPERATION 15.4-12
15.4.3.1 Identification of Causes and Accident 15.4-12
Description
15.4.3.2 Analysis of Effects and Consequences 15.4-13 15.4.3.3 Conclusions 15.4-16
15.4.4 STARTUP OF AN INACTIVE REACTOR COOLANT 15.4-16 PUMP AT AN INCORRECT TEMPERATURE
15.4.4.1 Identification of Causes and Accident 15.4-16 Description
15.4.4.2 Analysis of Effects and Consequences 15.4-17 15.4.4.3 Conclusions 15.4-18
15.4.5 A MALFUNCTION OR FAILURE OF THE FLOW 15.4-18 CONTROLLER IN A BWR LOOP THAT
RESULTS IN AN INCREASED REACTOR
COOLANT FLOW RATE
15.4.6 CHEMICAL AND VOLUME CONTROL SYSTEM 15.4-18 MALFUNCTION THAT RESULTS IN A
DECREASE IN THE BORON CONCENTRATION
IN THE REACTOR COOLANT
15.4.6.1 Identification of Causes and Accident 15.4-18 Description
15.4.6.2 Analysis of Effects and Consequences 15.4-20 15.4.6.3 Conclusions 15.4-22
15.4.7 INADVERTENT LOADING AND OPERATION OF 15.4-24
A FUEL ASSEMBLY IN IMPROPER POSITION
15.4.7.1 Identification of Causes and Accident 15.4-24
Description
15.4.7.2 Analysis of Effects and Consequences 15.4-25
15.4.7.3 Conclusions 15.4-26
15.4.8 SPECTRUM OF ROD CLUSTER CONTROL ASSEMBLY 15.4-26
EJECTION ACCIDENTS
15.4.8.1 Identification of Causes and Accident 15.4-26
Description
15.4.8.2 Analysis of Effects and Consequences 15.4-30
15.4.8.3 Radiological Consequences 15.4-36
15.4.8.4 Conclusions 15.4-41
15.
4.9 REFERENCES
15.4-41
15.0-v Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
Section Title Page
15.5 INCREASE IN REACTOR COOLANT INVENTORY 15.5-1
15.5.1 INADVERTENT OPERATION OF THE EMERGENCY 15.5-1
CORE COOLING SYSTEM DURING POWER
OPERATION
15.5.1.1 Identification of Causes and Accident 15.5-1
Description
15.5.1.2 Analysis of Effects and Consequences 15.5-2
15.5.1.3 Conclusions 15.5-4
15.5.2 CHEMICAL AND VOLUME CONTROL SYSTEM 15.5-5 MALFUNCTION THAT INCREASES REACTOR
COOLANT INVENTORY
15.5.2.1 Identification of Causes and Accident 15.5-5 Description
15.5.2.2 Analysis of Effects and Consequences 15.5-5
15.5.2.3 Conclusions 15.5-7
15.5.3 A NUMBER OF BWR TRANSIENTS 15.5-7
15.
5.4 REFERENCES
15.5-7
15.6 DECREASE IN REACTOR COOLANT INVENTORY 15.6-1
15.6.1 INADVERTENT OPENING OF A PRESSURIZER 15.6-1
SAFETY OR RELIEF VALVE
15.6.1.1 Identification of Cause and Accident 15.6-1
Description
15.6.1.2 Analysis of Effects and Consequences 15.6-2
15.6.1.3 Conclusions 15.6-3
15.6.2 BREAK IN INSTRUMENT LINE OR OTHER LINES 15.6-3
FROM REACTOR COOLANT PRESSURE BOUNDARY
THAT PENETRATE CONTAINMENT
15.6.2.1 Radiological Consequences 15.6-4
15.6.3 STEAM GENERATOR TUBE RUPTURE (SGTR) 15.6-7
15.6.3.1 Steam Generator Tube Rupture with Failure 15.6-7
of Faulted Steam Generator AFW Control Valve
15.6.3.1.1 Identification of Causes and Accident 15.6-7
Description
15.6.3.1.2 Analysis of Effects and Consequences 15.6-9
15.6.3.2 Steam Generator Tube Rupture with Postulated 15.6-12
Stuck-Open Atmospheric Relief Valve
15.6.3.2.1 Identification of Causes and Accident 15.6-12
Description
15.6.3.2.2 Analysis of Effects and Consequences 15.6-12
15.0-vi Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
Section Title Page
15.6.3.3 Radiological Consequences 15.6-14
15.6.3.4 Conclusions 15.6-17
15.6.3.5 References 15.6-18
15.6.4 SPECTRUM OF BWR STEAM SYSTEM PIPING 15.6-18
FAILURES OUTSIDE OF CONTAINMENT
15.6.5 LOSS-OF-COOLANT ACCIDENTS RESULTING 15.6-18
FROM A SPECTRUM OF POSTULATED PIPING
BREAKS WITHIN THE REACTOR COOLANT
PRESSURE BOUNDARY
15.6.5.1 Identification of Causes and Frequency 15.6-18
Classification
15.6.5.2 Sequence of Events and Systems Operations 15.6-19
15.6.5.3 Core and System Performance 15.6-21
15.6.5.4 Radiological Consequences 15.6-29
15.6.6 A NUMBER OF BWR TRANSIENTS 15.6-35
15.
6.7 REFERENCES
15.6-35
15.7 RADIOACTIVE RELEASE FROM A SUBSYSTEM OR 15.7-1 COMPONENT
15.7.1 RADIOACTIVE WASTE GAS DECAY TANK FAILURE 15.7-1
15.7.1.1 Identification of Causes 15.7-1
15.7.1.2 Sequence of Events and System Operations 15.7-1
15.7.1.3 Core and System Performance 15 7-2
15.7.1.4 Barrier Performance 15.7-2
15.7.1.5 Radiological Consequences 15.7-2
15.7.2 RADIOACTIVE LIQUID WASTE SYSTEM LEAK OR 15.7-5
FAILURE
15.7.2.1 Identification of Causes 15.7-5
15.7.2.2 Sequence of Events and System Operation 15.7-6
15.7.2.3 Core and System Performance 15.7-6
15.7.2.4 Barrier Performance 15.7-6
15.7.2.5 Radiological Consequences 15.7-6
15.7.3 POSTULATED RADIOACTIVE RELEASE DUE TO 15.7-9
LIQUID TANK FAILURES
15.7.4 FUEL HANDLING ACCIDENTS 15.7-9
15.7.4.1 Identification of Causes and Accident 15.7-9
Description
15.7.4.2 Sequence of Events and Systems Operations 15.7-9
15.7.4.3 Core and System Performance 15.7-9
15.7.4.4 Barrier Performance 15.7-9
15.7.4.5 Radiological Consequences 15.7-10
15.0-vii Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
Section Title Page
15.7.5 SPENT FUEL CASK DROP ACCIDENTS 15.7-17
15.8 ANTICIPATED TRANSIENTS WITHOUT SCRAM 15.8-1
App. 15A ACCIDENT ANALYSIS RADIOLOGICAL CONSEQUENCES 15A-1 EVALUATION MODELS AND PARAMETERS
15A.1 GENERAL ACCIDENT PARAMETERS 15A-1
15A.2 OFFSITE RADIOLOGICAL CONSEQUENCES 15A-1
CALCULATIONAL MODELS
15A.2.1 Accident Release Pathways 15A-1
15A.2.2 Single-Region Release Model 15A-2
15A.2.3a Two-Region Spray Model in Containment (LOCA) 15A-3 15A.2.3b Two-Region Release Model for Leakage 15A-5 Through RWST 15A.2.4 Offsite Thyroid Dose Calculational Model 15A-6 15A.2.5 Offsite Total-Body Dose Calculational Model 15A-7
15A.3 CONTROL ROOM RADIOLOGICAL CONSEQUENCES 15A-7 CALCULATIONAL MODELS
15A.3.1 Integrated Activity in Control Room 15A-7 15A.3.2 Control Room Thyroid Dose Calculational 15A-10 Model
15A.3.3 Control Room Beta-Skin Dose Calculational 15A-11 Model
15A.3.4 Control Room Total-Body Dose Calculation 15A-11 15A.3.4.1 Model for Radiological Consequences Due to 15A-12 Radioactive Cloud External to the
Control Room
15A.4 REFERENCES 15A-12
15.0-viii Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
LIST OF TABLES
Table No. Title
15.0-1 Nuclear Steam Supply System Power Ratings
15.0-2 Summary of Initial Conditions and Computer Codes Used
15.0-3 Nominal Values of Pertinent Plant Parameters Utilized
in the Accident Analyses
15.0-4 Trip Points and Time Delays to Trip Assumed in Accident
Analyses
15.0-5 Determination of Maximum Overpower Trip Point - Power
Range Neutron Flux Channel - Based on Nominal Setpoint
Considering Inherent Instrumentation Errors
15.0-6 Major Plant System and Equipment Available for Mitigation of Transient and Accident Conditions
15.0-7 Single Failures Assumed in Accident Analyses
15.0-8 Operator Actions Required for Small and Large LOCAs
15.0-9 Short Term Operator Actions Required for Steam
Generator Tube Rupture
15.1-1 Time Sequence of Events for Incidents that Result in
an Increase in Heat Removal by the Secondary System
15.1-2 Equipment Required Following a Rupture of a Main Steam
Line
15.1-3 Parameters Used in Evaluating the Radiological
Consequences of a Main Steam Line Break
15.1-4 Radiological Consequences of a Main Steam Line Break
15.2-1 Time Sequence of Events for Incidents Which Result in a
Decrease in Heat Removal by the Secondary System
15.2-2 Parameters Used in Evaluating Radiological Consequences
of Loss of Nonemergency AC Power
15.2-3 Radiological Consequences of Loss of Non-Emergency AC
Power
15.2-4 Natural Circulation Flow
15.0-ix Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
LIST OF TABLES
Table No. Title
15.3-1 Time Sequence of Events for Incidents Which Result in a
Decrease in Reactor Coolant System Flow Rate
15.3-2 Summary of Results for Locked Rotor Transients
15.3-3 Parameters Used in Evaluating the Radiological
Consequences of a Locked Rotor Accident
15.3-4 Radiological Consequences of a Locked Rotor Accident
15.4-1 Time Sequence of Events for Incidents Which Result in
Reactivity and Power Distribution Anomalies
15.4-2 Parameters Used in the Analysis of the Rod Cluster
Control Assembly Ejection Accident
15.4-3 Parameters Used in Evaluating the RCCA Ejection
Accident
15.4-4 Radiological Consequences of a Rod-Ejection Accident
15.5-1 Time Sequence of Events for Incidents Which Result in
an Increase in Reactor Coolant Inventory
15.6-1 Time Sequence of Events for Incident Which Results in a
Decrease in Reactor Coolant Inventory
15.6-2 Parameters Used in Evaluating the Radiological
Consequence of the CVCS Letdown Line Rupture Outside of
Containment
15.6-3 Radiological Consequences of a CVCS Letdown Line Break
Outside of Containment
15.6-4 Parameters Used in Evaluating the Radiological
Consequences of a Steam Generator Tube Rupture (SGTR)
With Forced Overfill
15.6-5 Radiological Consequences of a Steam Generator Tube
Rupture
15.0-x Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
LIST OF TABLES
Table No. Title
15.6-6 Parameters Used in Evaluating the Radiological
Consequences of a Loss-of-Coolant-Accident
15.6-7 Design Comparison to the Regulatory Positions of
Regulatory Guide 1.4 "Assumptions Used for Evaluating
the Potential Radiological Consequences of a Loss of
Coolant Accident for Pressurized Water Reactors," Revision 2, June 1974
15.6-8 Radiological Consequences of a Loss-of-Coolant Accident
15.6-9 Major Plant Parameter Assumptions Used in the BELOCA Analysis for Wolf Creek 15.6-9a Input Parameters Used in the Small Break LOCA Analysis 15.6-9b Summary of Peaking Factor Burndown Analyzed by the Best-Estimate Large-Break LOCA Analysis for Wolf Creek 15.6-10 Wolf Creek Best-Estimate Large-Break Sequence of Events for the Limiting PCT Case in Seconds
15.6-10a Time Sequence of Events for Small Break LOCA
15.6-11 Wolf Creek Best Estimate Large Break LOCA Results
15.6-12 Small Break LOCAs Results Fuel Cladding Data
15.6-13 Safety Injection Flow for BE Large Break LOCA Analysis
15.6-14 Safety Injection Pumped Flow Assumed for Small Break LOCAs
15.6-14a Pumped Safety Injection flow Rate Assumed for 8.75 inch Accumulator Line Break 15.7-1 Design Comparison to the Regulatory Positions of
Regulatory Guide 1.24 "Assumptions Used for Evaluating
the Potential Consequences of a Pressurized Water
Reactor Radioactive Gas Storage Tank Failure" Revision 0, Dated March 23, 1972 15.7-2 Design Comparison to the Regulatory Positions of
Regulatory Guide 1.25 "Assumptions Used for Evaluating
the Potential Radiological Consequences of a Fuel
Handling Accident in the Fuel Handling and Storage
Facility for Boiling and Pressurized Water Reactors"
Revision 0, Dated March 23, 1972 15.7-3 Parameters Used in Evaluating the Radiological
Consequences of a Waste Gas Decay Tank Rupture 15.7-4 Radiological Consequences of a Waste Gas Decay Tank
Rupture
15.7-5 Parameters Used in Evaluating the Radiological
Consequences of a Liquid Radwaste Tank Failure 15.0-xi Rev. 29 WOLF CREEK TABLE OF CONTENTS (CONTINUED)
LIST OF TABLES
Table No. Title
15.7-6 Radiological Consequences of a Liquid Radwaste Tank
Failure
15.7-7 Parameters Used in Evaluating the Radiological
Consequences of a Fuel Handling Accident
15.7-8 Radiological Consequences of a Fuel Handling Accident
15A-1 Parameters Used in Accident Analysis
15A-2 Limiting Short-term Atmospheric Dispersion Factors
(X/Qs) for Accident Analysis
15A-3 Fuel and Rod Gap Inventories - Core
15A-4 Dose Conversion Factors Used in Accident Analysis
15.0-xii Rev. 29 WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #*15.0-1 0 Illustration of Overtemperature and Overpower T Protection 15.0-2 0 Doppler Power Coefficient Used in Accident Analysis 15.0-3 0 RCCA Position Versus Time to Dashpot 15.0-4 0 Normalized Rod Worth Versus Percent Inserted 15.0-5 0 Normalized RCCA Bank Reactivity Worth Versus Normalized Drop Time 15.0-6 0 Minimum Moderator Density Coefficient Used in Analysis 15.0-7 0 Abbreviations and Symbols Used in Sequence Diagrams 15.0-8 0 Excessive Heat Removal Due to Feedwater Systems Malfunction 15.0-9 0 Excessive Load Increase 15.0-10 0 Depressurization of Main Steam System 15.0-11 0 Loss of External Load 15.0-12 0 Loss of Non-Emergency AC Power to the Station Auxiliaries 15.0-13 0 Loss of Normal Feedwater 15.0-14 0 Major Rupture of a Main Feedwater Line 15.0-15 0 Loss of Forced Reactor Coolant Flow 15.0-16 0 Uncontrolled Rod Cluster Control Assembly Bank Withdrawal 15.0-17 0 Dropped Rod Cluster Control Assembly 15.0-18 0 Single Rod Cluster Control Assembly Withdrawal at Full Power 15.0-19 0 Startup of an Inactive Reactor Coolant Loop 15.0-20 0 Boron Dilution 15.0-21 0 Rupture of Control Rod Drive Mechanism Housing 15.0-22 0 Inadvertent ECCS Operation at Power 15.0-23 0 Accidental Depressurization of Reactor Coolant System 15.0-24 0 Steam Generator Tube Rupture 15.0-25 0 Loss of Coolant Accident 15.0-26 0 CVCS Letdown Line Rupture 15.0-27 0 GWPS Gas Decay Tank Rupture 15.0-28 0 Floor Drain Tank Failure 15.0-29 0 Fuel Handling Accident in Fuel Building 15.0-30 0 Fuel Handling Accident Inside Containment 15.0-31 0 Spent Fuel Cask Drop Accident
15.0-xiii Rev. 29 WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #*15.1-1 0 Nuclear Power, and Pressurizer Pressure Transients for Feedwater Control Valve Malfunction 15.1-2 0 Reactor Coolant Loop T, and Core Heat Flux Transient for Feedwater Control Valve
Malfunction 15.1-2A 0 Core Average Temperature Transient and Minimum DNBR for Feedwater Control Valve Malfunction 15.1-3 0 Nuclear Power, Pressurizer Pressure and Water Volume Transients for Ten Percent Step Load Increase, Minimum Reactivity Feedback, Manual Reactor Control 15.1-4 0 DNBR and Vessel Average Temperature Transients for Ten Percent Step Load Increase, Minimum
Reactivity Feedback, Manual Reactor Control 15.1-5 0 Nuclear Power, Pressurizer Pressure and Water Volume Transients for Ten Percent Step Load
Increase, Maximum Reactivity Feedback, Manual Reactor Control 15.1-6 0 DNBR and Vessel Average Temperature Transients for Ten Percent Step Load Increase, Minimum Reactivity Feedback, Manual Reactor Control 15.1-7 0 Nuclear Power, Pressurizer Pressure and Water Volume Transients for Ten Percent Step Load
Increase Minimum Reactivity Feedback, Automatic
Reactor Control 15.1-8 0 DNBR and Vessel Average Temperature Transients for Ten Percent Step Load Increase, Minimum Reactivity Feedback, Automatic Reactor Control 15.1-9 0 Nuclear Power, Pressurizer Pressure and Water Volume Transients for Ten Percent Step Load Increase, Maximum Reactivity Feedback, Automatic Reactor Control 15.1-10 0 DNBR and Vessel Average Temperature Transients for Ten Percent Step Load Increase, Maximum
Reactivity Feedback, Automatic Reactor Control 15.1-11 0 K eff Versus Temperature 15.1-11a 0 Keff Versus Temperature SLB with Offsite Power 15.1-12 0 Failure of a Steam Generator Safety or Atmospheric Relief Valve 15.1-13 0 Failure of a Steam Generator Safety or Atmospheric Relief Valve 15.1-14 0 Doppler Power Feedback 15.1-15 0 Normalized Core Power and Normalized Core Heat Flux SLB with Offsite Power 15.1-16 0 Pressurizer Pressure and Pressurizer Liquid Volume SLB with Offsite Power
**The acronym FON, which is utilized on select Chapter 15 Figures, is defined
as fraction of nominal.
15.0-xiv Rev. 29 WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #*15.1-17 0 Core Inlet Temperature and Core Average Temperature SLB with Offsite Power 15.1-18 0 Total Core Reactivity and Core Boron Concentration SLB with Offsite Power 15.1-19 0 Normalized Feedwater Flow and Break Flow SLB with Offsite Power 15.1-20 0 Steamline Pressure and Core Inlet Flow SLB with Offsite Power 15.1-20a 0 SLB Transient at Hot-Zero Power with Offisite Power Available - Adj Minimum DNBR vs Time 15.1-21 0 Normalized Core Power and Normalized Core Heat Flux SLB Without Offsite Power 15.1-22 0 Pressurizer Pressure and Pressurizer liquid Volume SLB Without Offsite Power 15.1-23 0 Core Inlet Temperature and Core Average Temperature SLB Without Offsite Power 15.1-24 0 Total core Reactivity and core Boron Concentration SLB Without Offsite Power 15.1-25 0 Normalized Feedwater Flow and Break Flow SLB Without Offsite Power 15.1-26 0 Steamline Pressure and Core Inlet Flow SLB Without Offsite Power 15.2-1 0 Nuclear Power and Pressure for Turbine Trip Event with Minimum Reactivity Feedback Overpressure Evaluation 15.2-2 0 Pressurizer Liquid Volume and RCS Temperature for Turbine Trip Event with Minimum Reactivity
Feedback Overpressure Evaluation 15.2-3 0 Nuclear Power and Pressure for Turbine Trip Event with Maximum Reactivity Feedback Overpressure Evaluation 15.2-4 0 Pressurizer Liquid Volume and RCS Temperature for Turbine Trip Event with Maximum Reactivity Feedback Overpressure Evaluation 15.2-5 0 Nuclear Power and Pressure for Turbine Trip Event with Minimum Reactivity Feedback DNB
Evaluation 15.2-6 0 Pressurizer Liquid Volume and RCS Temperature for Turbine Trip Event with Minimum Reactivity
Feedback DNB Evaluation 15.2-7 0 Nuclear Power and Pressure for Turbine Trip Event With Maximum Reactivity Feedback DNB Evaluation 15.2-8 0 Pressurizer Liquid Volume and RCS Temperature for Turbine Trip Event With Maximum Reactivity Feedback DNB Evaluation
**The acronym FON, which is utilized on select Chapter 15 Figures, is defined
as fraction of nominal.
15.0-xv Rev. 29 WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #* 15.2-9 0 Nuclear Power, Reactor Coolant Mass Flow Rate and Steam Generator Pressure Transients for Loss of AC Power 15.2-10 0 Reactor Coolant Temperature, Maximum RCS Pressure and Pressurizer Liquid Level for Loss
of AC Power 15.2-11 0 Nuclear Power and Steam Generator Pressure Transients for Loss of Normal Feedwater 15.2-12 0 Core Average Temperature, Maximum RCS Pressure and Pressurizer Liquid Level Transients for
Loss of Normal Feedwater 15.2-13 0 Nuclear Power, Core Heat Flux and Total Core Reactivity Transients for Main Feedwater Line
Rupture with Offsite Power Available 15.2-14 0 Pressurizer and Maximum System Pressure and Pressurizer Water Volume for Main Feedwater
Line Rupture with Offsite Power Available 15.2-15 0 Reactor Coolant Flow and Feedwater Line Break Flow for Main Feedwater Line Rupture with
Offsite Power Available 15.2-16 0 Reactor Coolant Temperature (Faulted Loop) and Reactor Coolant Temperature (Intact Loop) for Main Feedwater Line Rupture with Offsite Power Available 15.2-17 0 Steam Generator Pressure for Main Feedwater Line Rupture with Offsite Power Available 15.2-18 0 Nuclear Power, Core Heat Flux and Total Core Reactivity for Main Feedwater Line Rupture
Without Offsite Power 15.2-19 0 Pressurizer and Maximum System Pressure and Pressurizer Water Volume for Main Feedwater
Line Rupture Without Offsite Power 15.2-20 0 Reactor Coolant Flow and Feedwater Line Break Flow for Main Feedwater Line Rupture Without Offsite Power 15.2-21 0 Faulted Loop and Intact Loop Reactor Coolant Temperature for Main Feedwater Line Rupture Without Offsite Power 15.2-22 0 Steam Generator Pressure for Main Feedwater Line Rupture Without Offsite Power 15.3-1 0 Pressurizer Pressure Transient for Four Loops in Operation, Two Pumps Coasting Down 15.3-2 0 Total Core Flow Transient for Four Loops in Operation, Two Pumps Coasting Down 15.3-3 0 Faulted Loop Flow Transient for Four Loops in Operation, Two Pumps Coasting Down
**The acronym fon, which is utilized on select Chapter 15 Figures, is defined
as fraction of nominal.
15.0-xvi Rev. 29 WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #*15.3-4 0 Nuclear Power Transient for Four Loops in Operation, Two Pumps Coasting Down 15.3-5 0 Core Heat Flux and Core Average Temperature for Four Loops in Operation, Two Pumps Coasting Down 15.3-6 0 DNBR Transient for Four Loops in Operation, Two Pumps Coasting Down 15.3-7 0 Total Core Flow Transient for Four Loops in Operation, Four Pumps Coasting Down 15.3-8 0 Pressurizer Pressure Transient for Four Loops in Operation, Four Pumps Coasting Down 15.3-9 0 Normalized Core Power Transient for Four Loops in Operation, Four Pumps Coasting Down 15.3-10 0 Core Heat Flux Transient for Four Loops in Operation, Four Pumps Coasting Down 15.3-11 0 Core Average Temperature for Four Loops in Operation, Four Pumps Coasting Down 15.3-12 0 DNBR Transient for Four Loops in Operation, Four Pumps Coasting Down 15.3-13 0 Peak RCS Pressure Transient, Locked Rotor With and Without Offsite Power 15.3-14 0 Total Core Flow Transient, Locked Rotor With and Without Offsite Power 15.3-15 0 Faulted Loop Flow Transient, Locked Rotor With and Without Offsite Power 15.3-16 0 Normalized Power Transient, Locked Rotor With and Without Offsite Power 15.3-17 0 Core Heat Flux Transient, Locked Rotor With and Without Offsite Power 15.3-18 0 Core Average Temperature, Locked Rotor With and Without Offsite Power 15.3-19 0 Outer Clad Temperature for Locked Rotor Without Offsite Power 15.4-1 0 Core Average Neutron Flux Transient for Uncontrolled Rod Withdrawal from a Subcritical
Condition 15.4-2 0 Thermal Flux Transient for Uncontrolled Rod Withdrawal from a Subcritical Condition 15.4-3 0 Fuel and Clad Temperature Transient for Uncontrolled Rod Withdrawal from a Subcritical
Condition 15.4-4 0 Uncontrolled RCCA Bank Withdrawal from Full Power with Minimum Reactivity Feedback (5 pcm/sec Withdrawal Rate) 15.4-4a 0 Core Power - Uncontrolled RCCA Bank Withdrawal at Power (DNB Limiting Case)
15.0-xvii Rev. 29 WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #* 15.4-4b 0 Exit Core Pressure - Uncontrolled RCCA Bank Withdrawal at Power (DNB Limiting Case) 15.4-4c 0 RCS Tavg - Uncontrolled RCCA Bank Withdrawal at Power (DNB Limiting Case) 15.4-4d 0 Flux Ratio - Uncontrolled RCCA Bank Withdrawal at Power (DNB Limiting Case) 15.4-4e 0 Core Exit Enthalpy - Uncontrolled RCCA Bank Withdrawal at Power (DNB Limiting Case) 15.4-4f 0 Core Inlet Flow - Uncontrolled RCCA Bank Withdrawal at Power (DNB Limiting Case) 15.4-4g 0 Minimum DNB - Uncontrolled RCCA Bank Withdrawal at Power (DNB Limiting Case) 15.4-5 0 Uncontrolled RCCA Bank Withdrawal from Full Power with Minimum Reactivity Feedback (5 pcm/sec Withdrawal Rate) 15.4-5a 0 Minimum DNBR - Uncontrolled RCCA Bank Withdrawal (100% Power) 15.4-5b 0 Minimum DNBR - Uncontrolled RCCA Bank Withdrawal at Power (60% Power) 15.4-5c 0 Minimum DNBR - Uncontrolled RCCA Bank Withdrawal at Power (10% Power) 15.4-6 0 Withdrawal from Full Power with Beginning-of-Life Reactivity, (5 pcm/sec Withdrawal Rate) 15.4-6a 0 Core Power - Uncontrolled RCCA Bank Withdrawal at Power (RCS Overpressure Limiting Case) 15.4-6b 0 RCS Tavg - Uncontrolled RCCA Bank Withdrawal at Power (RCS Overpressure Limiting Case) 15.4-6c 0 Maximum RCS Pressure - Uncontrolled RCCA Bank Withdrawal at Power (RCS Overpressure Limiting Case) 15.4-7 0 Minimum DNBR Versus Reactivity Insertion Rate, Rod Withdrawal from 100-Percent Power 15.4-7a 0 Core Power - Uncontrolled RCCA Bank Withdrawal at Power (Pressurizer Overfill Limiting Case) 15.4-7b 0 RCS Tavg - Uncontrolled RCCA Bank Withdrawal at Power (Pressurizer Overfill Limiting Case) 15.4-7c 0 Pressurizer Level - Uncontrolled RCCA Bank Withdrawal at Power (Pressurizer Overfill Limiting Case) 15.4-8 0 Removed 15.4-9 0 Removed 15.4-10 0 Nuclear Power Transient and Core Heat Flux Transient for Dropped Rod Cluster Control
Assembly 15.4-11a 0 Pressurizer Pressure Transient and Core Average Temperature Transient for Dropped Rod Cluster Control Assembly
15.0-xviii Rev. 25 WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #*15.4-11b 0 Deleted 15.4-12 0 Nuclear Power Transient for Startup of an Inactive Reactor Coolant Loop 15.4-13 0 Core Flow Transient for Startup of an Inactive Reactor Coolant Loop 15.4-14 0 Pressurizer Pressure Transient for Startup of an Inactive Reactor Coolant Loop 15.4-15 0 Core Average Temperature and Pressurizer Pressure Transient for Startup of an Inactive Reactor Coolant Loop 15.4-16 0 DNBR Transient for Startup of an Inactive Reactor Coolant Loop 15.4-17 0 Representative Percent Change in Local Assembly Average Power for an Interchange Between a
Region 1 and a Region 3 Assembly 15.4-18 0 Representative Percent Change in Local Assembly Average Power for an Interchange Between a Region 1 and a Region 2 Assembly with the Burnable Poison Rods Being Retained by the
Region 2 Assembly 15.4-19 0 Representative Percent Change in Local Assembly Average Power for an Interchange Between a
Region 1 and a Region 2 Assembly with the
Burnable Poison Rods Being Transferred to the Region 1 Assembly 15.4-20 0 Representative Percent Change in Local Assembly Average Power for an Enrichment Error (A Region 2 Assembly Loaded into the Core Central
Position) 15.4-21 0 Representative Percent Change in Local Assembly Average Power for Loading a Region 2 Assembly
into a Region 1 Position Near the Core
Periphery 15.4-22 0 Nuclear Power Transient, BOL, HFP, Rod Ejection Accident 15.4-23 0 Fuel Centerline, Fuel Average, and Cladding Surface Temperature Transients, BOL, HFP, Rod
Ejection Accident 15.4-24 0 Nuclear Power Transient, EOL, HZP, Rod Ejection Accident 15.4-25 0 Fuel Centerline, Fuel Average, and Cladding Surface Temperature Transients, EOL, HZP, Rod
Ejection Accident 15.4-26 0 Steam Generator Secondary Pressure Transient for Rod Ejection Analysis 15.4-27 0 RCS Pressure Transient for Rod Ejection Analysis 15.4-28 0 Reactor Coolant System Integrated Break Flow Following a Rod Ejection Accident 15.5-1 0 Inadvertent Operation of ECCS During Power Operation 15.5-2 0 Inadvertent Operation of ECCS During Power Operation 15.0-xix Rev. 25 WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #*15.5-3 0 Inadvertent Operation of ECCS During Power Operation 15.5-4 0 Chemical and Volume Control System Malfunction Maximum Reactivity Feedback with Pressurizer Spray 15.5-5 0 Chemical and Volume Control System Malfunction Maximum Reactivity Feedback with Pressurizer
Spray 15.5-6 0 Chemical and Volume Control System Malfunction Maximum Reactivity Feedback without Pressurizer
Spray 15.5-7 0 Chemical and Volume Control System Malfunction Maximum Reactivity Feedback without Pressurizer
Spray 15.5-8 0 Chemical and Volume Control System Malfunction Minimum Reactivity Feedback with Pressurizer
Spray 15.5-9 0 Chemical and Volume Control System Malfunction Minimum Reactivity Feedback with Pressurizer
Spray 15.5-10 0 Chemical and Volume Control System Malfunction Minimum Reactivity Feedback without Pressurizer Spray 15.5-11 0 Chemical and Volume Control System Malfunction Minimum Reactivity Feedback without Pressurizer Spray 15.6-1 0 Nuclear Power, Pressurizer Pressure and Reactor Coolant Average Temperature for Inadvertent
Opening of a Pressurizer Safety Valve 15.6-2 0 DNBR Transient for Inadvertent Opening of a Pressurizer Safety Valve 15.6-3A 0 Pressurizer Pressure Transient SGTR Forced with Stuck Open Steam Generator Safety Valve 15.6-3B 0 Faulted Loop RCS Temperature Transients SGTR Forced Overfill with Stuck Open Steam Generator
Safety Valve 15.6-3C 0 Intact Loop RCS Temperature Transients SGTR Forced Overfill with Stuck Open Steam Generator Safety Valve 15.6-3D 0 Steam Generator Pressure Transients SGTR Forced Overfill with Stuck Open Steam Generator Safety Valve 15.6-3E 0 Steam Generator Temperature Transients SGTR Forced Overfill with Stuck Open Steam Generator
Safety Valve 15.6-3F 0 Pressurizer Water Level Transient SGTR Forced Overfill with Stuck Open Steam Generator Safety
Valve 15.6-3G 0 Faulted Steam Generator Steam Flow Transient SGTR Forced Overfill with Stuck Open Steam
Generator Safety Valve 15.0-xx Rev. 29
WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #*15.6-3H 0 Faulted Steam Generator AFW Flow and Narrow Range Level Transient SGTR Forced Overfill with Stuck Open Steam Generator Safety Valve 15.6-3I 0 Faulted Steam Generator Break Flow Transient SGTR Forced Overfill with Stuck Open Steam
Generator Safety Valve 15.6-3J 0 Faulted Steam Generator Mixture Volume Transient SGTR Forced Overfill with Stuck Open
Steam Generator Safety Valve 15.6-3K 0 Pressurizer Pressure Transient SGTR W/Stuck-Open ARV 15.6-3L 0 Faulted Loop RCS Temperature SGTR W/Stuck-Open ARV 15.6-3M 0 Intact Loop RCS Temperature Transient SGTR W/Stuck-Open ARV 15.6-3N 0 Steam Generator Pressure (Stuck-Open ARV) 15.6-3O 0 Steam Generator Temperature Transient SGTR W/Stuck-Open ARV 15.6-3P 0 Pressurizer Water Level Transient SGTR W/Stuck-Open ARV 15.6-3Q 0 Faulted SG Steam Flow Transient SGTR (Stuck-Open ARV) 15.6-3R 0 Faulted SG-AFW Flow and Indicated Narrow Range Level Transient SGTR (Stuck-Open ARV) 15.6-3S 0 Faulted SG-Total Break Flow Transient SGTR (Stuck-Open ARV) 15.6-3T 0 Faulted SG-Mixture Volume Transient SGTR (Stuck-Open ARV) 15.6-4 0 DELETED 15.6-5 0 Code Scaling, Applicability, and Uncertainty (CSAU) Evaluation Methodology 15.6-6 0 Code Interface Description for Small Break Model 15.6-7 0 HOTSPOT, Cladding Temperature Transient and WC/T PCT for the Limiting PCT Case 15.6-8 0 PCT Elevation for the Hot Rod for the Limiting PCT Case 15.6-9 Break Flow for the Limiting PCT Case 15.6-10 0 Void Fraction in the Reactor Coolant Pumps for the Limiting PCT Case 15.6-11 0 Vapor Flow in the Hot Assembly Channel for the Limiting PCT Case 15.6-12 0 Pressurizer Pressure for the Limiting PCT Case 15.6-12a 0 DELETED 15.6-12b 0 DELETED 15.6-12c 0 DELETED 15.6-12d 0 DELETED 15.6-12e 0 DELETED 15.6-12f 0 DELETED
15.0-xxi Rev. 29 WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #*15.6-12g 0 DELETED 15.6-12h 0 DELETED 15.6-12i 0 DELETED 15.6-13 0 Lower Plenum Collapsed Liquid Level for the Limiting PCT Case 15.6-14 0 Accumulator Injection Flow for the Limiting PCT Case 15.6-15 0 Safety Injection Flow (HHSI) for the Limiting PCT Case 15.6-16 0 Safety Injection Flow (IHSI + RHR) for the Limiting PCT Case 15.6-17 0 Downcomer Collapsed Liquid Level for the Limiting PCT Case 15.6-18 0 Collapsed Liquid Level in Core Average Channel for the Limiting PCT Case 15.6-19 0 Vessel liquid mass for the Limiting PCT Case 15.6-20 0 Deleted 15.6-21 0 Analysis vs. Calculated Containment Back Pressure 15.6-22 0 Wolf Creek BELOCA Analysis Axial Power Shape Operating Space Envelope 15.6-23 0 DELETED 15.6-24a 0 DELETED 15.6-24b 0 DELETED 15.6-25 0 DELETED 15.6-26 0 DELETED 15.6-27 0 DELETED
15.0-xxii Rev. 29 WOLF CREEK CHAPTER 15 - LIST OF FIGURES
*Refer to Section 1.6 and Table 1.6-3. Controlled drawings were removed from the USAR at Revision 17 and are considered incorporated by reference.
Figure # Sheet T itle Drawing #*15.6-28 0 DELETED 15.6-29 0 DELETED 15.6-30 0 DELETED 15.6-31 0 Reactor Coolant System Depressurization Transient (3 inch break) 15.6-32 0 Core Mixture Level (3 inch break) 15.6-33 0 Clad Temperature Transient Hot Spot (3 inch break) 15.6-34 0 Steam Flow (3 inch break) 15.6-35 0 Rod Film Heat Transfer Coefficient (3 inch break) 15.6-36 0 Hot Spot Fluid Temperature (3 inch break) 15.6-37 0 Reactor Coolant System Depressurization Transient (2 inch break) 15.6-38 0 Reactor Coolant System Depressurization Transient (4 inch break) 15.6-39 0 Reactor Coolant System Depressurization Transient (6 inch break) 15.6-40 0 Core Mixture Level (2 inch break) 15.6-41 0 Core Mixture Level (4 inch break) 15.6-42 0 Core Mixture Level (6 inch break) 15.6-43 0 Clad Temperature Transient Hot Rod (2 inch break) 15.6-44 0 Clad Temperature Transient Hot Rod (4 inch break) 15.6-45 0 Clad Temperature Transient Hot Rod (6 inch break) 15.6-46 0 Safety Injection Flowrate 15.6-47 0 Small Break Power Distribution 15.6-48 0 Core Power(including Residual Fission) After Reactor Trip (Applies to All Small Breaks) 15.A-1 0 Release Pathways
15.0-xxiii Rev. 29 WOLF CREEK15.0 ACCIDENT ANALYSIS 15.0.1 CLASSIFICATION OF PLANT CONDITIONS Since 1970, the American Nuclear Society (ANS) classification of plant conditions divides plant conditions into four categories in accordance with anticipated frequency of occurrence and potential radiological consequences to the public. The four categories are as follows:
- a. Condition I*: Normal operation and operational transients
- b. Condition II*: Faults of moderate frequency
- c. Condition III*: Infrequent faults
- d. Condition IV*: Limiting faults The basic principle applied in relating design requirements to each of the conditions is that the most probable occurrences should yield the least radiological risk to the public, and those extreme situations having the potential for the greatest risk to the public shall be those least likely to
occur. Where applicable, reactor trip and engineered safeguards system
functioning is assumed to the extent allowed by considerations, such as the
single failure criterion, in fulfilling this principle, (i.e. only seismic
Category I, Class IE, and IEEE qualified equipment, instrumentation, and
components are used in the ultimate mitigation of the consequences of faulted
conditions Condition II, III and IV events). Step-by-step sequence-of-events
diagrams are provided for each transient in Figures 15.0-8 through 15.0-31.
Figure 15.0-7 provides the legend used in these diagrams. The accident
analysis radiological consequences evaluation models and parameters are discussed in Appendix 15A.15.0.1.1 Condition I - Normal Operation and Operational Transients Condition I occurrences are those which are expected frequently in the course of power operation, refueling, maintenance, or maneuvering of the plant. As
such, Condition I occurrences are accommodated with margin between any plant parameter and the value of that parameter which would require either automatic or manual protective action. Inasmuch as Condition I events occur
- For the definition of Conditions I, II, III, and IV events, refer to ANSI-N18.2, "Nuclear Safety Criteria for the Design
of Stationary PWR Plants," Section 5, 1973.15.0-1Rev. 0 WOLF CREEK frequently, they must be considered from the point of view of their effect on the consequences of fault conditions (Conditions II, III, and IV). In this
regard, analysis of each fault condition described is generally based on a
conservative set of initial conditions corresponding to adverse conditions that
can occur during Condition I operation. A typical list of Condition I events is given below:
- a. Steady state and shutdown operations
- 1. Power operation
- 2. Startup
- 3. Hot standby
- 4. Hot shutdown
- 5. Cold shutdown
- 6. Refueling
- b. Operation with permissible deviations
Various deviations from normal operation but specifically allowed by the Technical Specifications which may occur during continued operation are considered in conjunction with other operational modes.
These include:
- 1. Operation with components or systems out of service (such as an inoperable RCCA)
- 2. Leakage from fuel with limited clad defects
- 3. Excessive radioactivity in the reactor coolant
(a) Fission products (b) Corrosion products
(c) Tritium
- 4. Operation with steam generator leaks
- 5. Testing15.0-2Rev. 0 WOLF CREEK
- c. Operational transients
- 1. Plant heatup and cooldown
- 2. Step load changes (up to
+/- 10 percent)
- 3. Ramp load changes (up to 5 percent/minute)
- 4. Load rejection up to and including design full load rejection transient15.0.1.2 Condition II - Faults of Moderate Frequency These faults, at worst, result in a reactor trip with the plant being capable of returning to operation. These faults (or events) do not propagate to cause a more serious fault, i.e., Condition III or IV events. In addition, Condition II events are not expected to result in fuel rod failures or reactor coolant system or secondary system overpressurization. The following faults are included in this category:
- a. Feedwater system malfunctions that result in a decrease in feedwater temperature (Section 15.1.1).
- b. Feedwater system malfunctions that result in an increase in feedwater flow (Section 15.1.2).
- c. Excessive increase in secondary steam flow (Section 15.1.3). d. Inadvertent opening of a steam generator atmospheric relief or safety valve (Section 15.1.4).
- e. Loss of external electrical load (Section 15.2.2).
- f. Turbine trip (Section 15.2.3).
- g. Inadvertent closure of main steam isolation valves (Section 15.2.4).
- h. Loss of condenser vacuum and other events resulting in turbine trip (Section 15.2.5).
- i. Loss of nonemergency ac power to the station auxiliaries (Section 15.2.6).
- j. Loss of normal feedwater flow (Section 15.2.7).15.0-3Rev. 13 WOLF CREEK
- k. Partial loss of forced reactor coolant flow (Section 15.3.1).
- l. Uncontrolled rod cluster control assembly bank withdrawal from a subcritical or low power startup condition (Section 15.4.1).
- m. Uncontrolled rod cluster control assembly bank withdrawal at power (Section 15.4.2).
- n. Rod cluster control assembly misalignment (dropped RCCA, dropped RCCA bank, or statically misaligned RCCA)
(Section 15.4.3).
- o. Startup of an inactive reactor coolant pump at an incorrect temperature (Section 15.4.4).
- p. Chemical and volume control system malfunction that results in a decrease in the boron concentration in the
reactor coolant (Section 15.4.6).
- q. Inadvertent operation of the emergency core cooling system during power operation (Section 15.5.1).
- r. Chemical and volume control system malfunction that increases reactor coolant inventory (Section 15.5.2).
- s. Inadvertent opening of a pressurizer safety or relief valve (Section 15.6.1).
- t. Break in instrument line or other lines from reactor coolant pressure boundary that penetrate the containment
(Section 15.6.2).15.0.1.3 Condition III - Infrequent Faults Condition III events are faults which may occur very infrequently during the life of the plant. They may result in the failure of only a small fraction of the fuel rods. The release of radioactivity will not be sufficient to interrupt or restrict public use of those areas beyond the exclusion area boundary, per the guidelines of 10 CFR 100. A Condition III event will not, by itself, generate a Condition IV event or result in a consequential loss of
function of the reactor coolant system or containment barriers. The following faults are included in this category:
- a. Steam system piping failure (minor) (Section 15.1.5).15.0-4Rev. 0 WOLF CREEK
- b. Complete loss of forced reactor coolant flow (Section 15.3.2).
- c. Rod cluster control assembly misalignment (single rod cluster control assembly withdrawal at full power)
(Section 15.4.3).
- d. Inadvertent loading and operation of a fuel assembly in an improper position (Section 15.4.7).
- e. Loss-of-coolant accidents resulting from a spectrum of postulated piping breaks within the reactor coolant pressure boundary (small break) (Section 15.6.5).
- f. Radioactive gas waste system leak or failure (Section 15.7.1).
- g. Radioactive liquid waste system leak or failure (Section 15.7.2).
- h. Postulated radioactive releases due to liquid tank failures (Section 15.7.3).
- i. Spent fuel cask drop accidents (Section 15.7.5).15.0.1.4 Condition IV - Limiting Faults Condition IV events are faults which are not expected to take place, but are postulated because their consequences would include the potential of the
release of significant amounts of radioactive material. They are the most drastic which must be designed against and represent limiting design cases. Condition IV events are not to cause a fission product release to the environment resulting in doses in excess of guideline values of 10 CFR 100. A single Condition IV event is not to cause a consequential loss of required
functions of systems needed to cope with the fault, including those of the emergency core cooling system and the containment. The following faults have been classified in this category:
- a. Steam system piping failure (major) (Section 15.1.5).
- b. Feedwater system pipe break (Section 15.2.8).
- c. Reactor coolant pump shaft seizure (locked rotor)
(Section 15.3.3).
- d. Reactor coolant pump shaft break (Section 15.3.4).15.0-5Rev. 0 WOLF CREEK
- e. Spectrum of rod cluster control assembly ejection accidents (Section 15.4.8).
- f. Steam generator tube failure (Section 15.6.3).
- g. Loss-of-coolant accidents, resulting from the spectrum of postulated piping breaks within the reactor coolant
pressure boundary (large break) (Section 15.6.5).
- h. Design basis fuel handling accidents (Section 15.7.4).
15.0.2 OPTIMIZATION OF CONTROL SYSTEMS A control system setpoint study is performed prior to operation to simulate performance of the reactor control and protection systems. In this study, emphasis is placed on the development of a control and protection system which will automatically maintain prescribed conditions in the plant even under the most adverse set of anticipated plant operating transients with respect to both
system stability and equipment performance. For each mode of plant operation, a group of optimum controller setpoints is determined. A consistent set of
control system parameters is derived from this study that satisfies plant
operational requirements throughout the core life and for various levels of
power operation. The study is comprised of an analysis of the following control systems: rod cluster control assembly, steam dump, steam generator level, pressurizer pressure, and pressurizer level. 15.0.3 PLANT CHARACTERISTICS AND INITIAL CONDITIONS ASSUMED IN THE ACCIDENT ANALYSES15.0.3.1 Design Plant Conditions Table 15.0-1 lists the principal power rating values which are assumed for the transients analyzed. Two ratings are given:
- a. The guaranteed NSSS thermal power output. This power output includes the thermal power generated by the reactor coolant pumps. b. The rated reactor core thermal power output is 3565 MWt.15.0-6Rev. 7 WOLF CREEK Allowances for errors in the determination of the steady-state power level are made as described in Section 15.0.3.2. The core thermal power used for each
transient is given in Table 15.0-2. The values of other pertinent plant parameters utilized in the accident analyses are given in Table 15.0-3.15.0.3.2 Initial Conditions For transients in which DNB is of concern, the WCGS Stastitical Core Design (SCD) methodology (Ref 14) is used. In application of this methodology, the
following steady-state errors are considered:a.Core powerNominalb.Average reactor coolant +/-1.65°F to allow forsystem temperaturesteam generator foulingc.Pressurizer pressureNominal For transients in which RCS overpressurization or pressurizer overfill is of concern the following steady-state errors are considered:
- a. Core power +2 percent allowance for calorimetric error b. Average reactor coolant +4.85°F allowance for system temperature controller deadband and measurement error plus an additional 1.65°F allow-ance for steam generator fouling c. Pressurizer pressure +30 psi allowance for steady state fluctua-tions and measurement
errors Table 15.0-2 summarizes the initial conditions and computer codes used in the accident analyses.15.0-7Rev. 12 WOLF CREEK15.0.3.3 Power Distribution The transient response of the reactor system is dependent on the initial power distribution. The nuclear design of the reactor core minimizes adverse power
distribution through the placement of fuel assemblies and control rods. Power distribution may be characterized by the nuclear enthalpy rise hot channel factor (F DH) and the total peaking factor (F q). Unless specifically noted otherwise, the peaking factors used in the accident analyses are those presented in Chapter 4.0. For transients which may be DNB limited, the radial peaking factor is of importance. The radial peaking factor increases with decreasing power level due to rod insertion. This increase in F DH is included in the core limits illustrated in Figure 15.0-1. All transients that may be DNB limited are assumed to begin with a F DH consistent with the initial power level defined in the Technical Specifications. The axial power shape used in the DNB calculation is the 1.55 chopped cosine,as discussed in Chapter 4 for transients analyzed at full power and the most limiting power shape calculated or allowed for accidents initiated at non-full power or asymmetric RCCA conditions.The radial and axial power distributions described above are input to the VIPREcode, as described in Chapter 4. For transients which may be overpower limited, the total peaking factor (F q) is of importance. All transients that may be over-power limited are assumed to begin with plant and reactor operating conditions consistent with the restrictions defined in the Technical Specifications. For overpower transients that are slow with respect to the fuel rod thermal time constant, for example the chemical and volume control system malfunction that results in a slow decrease in the boron concentration in the reactor coolant system as well as an excessive increase in secondary steam flow, that may reach equilibrium without causing a reactor trip, the fuel rod thermalevaluations are performed as discussed in Chapter 4. For overpower transients that are fast with respect to the fuel rod thermal time constant, for example, the uncontrolled RCCA bank withdrawal from subcritical or low power startup and RCCA ejection incident, both of which result in a large power rise over a few seconds, a detailed fuel transient heat transfer calculation must be performed.15.0-8Rev. 7 WOLF CREEK 15.0.4 REACTIVITY COEFFICIENTS ASSUMED IN THE ACCIDENT ANALYSES The transient response of the reactor system is dependent on reactivity feedback effects, in particular the moderator temperature coefficient and the Doppler power coefficient. These reactivity coefficients are discussed indetail in Section 4.3.2.3 and shown on Figure 15.0-6. In the analysis of certain events, conservatism requires the use of large reactivity coefficient values, whereas in the analysis of other events conservatism requires the use of small reactivity coefficient values. Some analyses, such as loss of reactor coolant from cracks or ruptures in the reactor coolant system, do not depend on reactivity feedback effects. The values used are given in Table 15.0-2. Reference is made in that table to Figure 15.0-2, which shows the upper and lower bound Doppler power coefficients as a function of power, used in the transient analysis. The justification for use of conservatively large versus small reactivity coefficient values are
treated on an event-by-event basis. In some cases, conservative combinations of parameters are used to bound the effects of core life. For example, in a
load increase transient it is conservative to use a small Doppler defect and a
small moderator coefficient. 15.0.5 ROD CLUSTER CONTROL ASSEMBLY INSERTION CHARACTERISTICS
All accident analysis results contained herein are applicable to both Ag-In-Cd and hafnium control rods. The negative reactivity insertion following a reactor trip is a function of the acceleration of the RCCAs as a function of time and the variation in rod worth
as a function of rod position. For accident analyses, the critical parameter
is the time of insertion up to the dashpot entry, or approximately 85 percent
of the rod cluster travel. The RCCA position versus time assumed in accident
analyses is shown in Figure 15.0-3. The RCCA insertion time to dashpot entry
is taken as 2.7 seconds unless otherwise noted in the discussion. The use of
such a long insertion time provides conservative results for all accidents and
is intended to be applicable to all types of RCCAs, which may be used
throughout plant life. Drop time testing requirements are specified in the
plant Technical Specifications. Figure 15.0-4 shows the fraction of total negative reactivity insertion versus normalized rod position for a core where the axial distribution is skewed to
the lower region of the core. An axial distribution which is skewed to the lower region of the core can arise from an unbalanced xenon distribution. This curve is used to compute the negative reactivity insertion versus time following a reactor trip, which is input to all point kinetics15.0-9Rev. 13 WOLF CREEK core models used in transient analyses. The bottom skewed power distribution itself is not an input into the point kinetics core model. There is inherent conservatism in the use of Figure 15.0-4 in that it is based on a skewed flux distribution which would exist relatively infrequently. For cases other than those associated with unbalanced xenon distributions, significantly more negative reactivity would have been inserted than that shown
in the curve, due to the more favorable axial distribution existing prior to
trip.The normalized RCCA negative reactivity insertion versus time is shown in Figure 15.0-5. The curve shown in this figure was obtained from Figures 15.0-3 and 15.0-4. A total negative reactivity insertion following a trip of 4-percentk is assumed in the transient analyses, except where specifically noted otherwise. This assumption is conservative with respect to the calculated trip reactivity worth available, as shown in Table 4.3-3. For Figures 15.0-3 and 15.0-4, the RCCA drop time is normalized to 2.7 seconds, unless otherwise noted for a particular event, in order to provide a bounding analysis for all RCCAs to be used in the WCGS core. The normalized RCCA negative reactivity insertion versus time curve for an axial power distribution skewed to the bottom (Figure 15.0-5) is used in those
transient analyses for which a point kinetics core model is used. Where
special analyses require use of three-dimensional or axial one-dimensional core
models, the negative reactivity insertion resulting from the reactor trip is calculated directly by the reactor kinetics code, and is not separable from the
other reactivity feedback effects. In this case, the RCCA position versus time of Figure 15.0-3 is used as code input. 15.0.6 TRIP POINTS AND TIME DELAYS TO TRIP ASSUMED IN ACCIDENT ANALYSES A reactor trip signal acts to open two trip breakers connected in series feeding power to the control rod drive mechanisms. The loss of power to the
mechanism coils causes the mechanisms to release the RCCAs, which then fall by
gravity into the core. There are various instrumentation delays associated with
each trip function, including delays in signal actuation, in opening the trip breakers, and in the release of the rods by the mechanisms. The total delay to trip is defined as the time delay from the time that trip conditions are
reached to the time the rods are free and15.0-10Rev. 6 WOLF CREEK begin to fall. The safety analysis trip setpoints assumed in accident analyses
and the time delay assumed for each trip function are given in Table 15.0-4. Reference is made in that table to overtemperature and overpower T trip shown in Figure 15.0-1. Figure 15.0-1 shows the core thermal limits over the range of allowable operating pressures assuming a maximum loop Thermal Design Flow (TDF) of 90,324 gpm. The DNB limit lines correspond to a safety analysis limit
DNBR value as determined by the WRB-2 CHF Correlation (see Section
4.4.1.1)(Reference 16). The figure demonstrates the adequacy of the
Overtemperature and Overpower Delta T trip functions in conjunction with the
steam generator safety valve lift settings to protect the core thermal limits.
The manner in which the combination of overpower and overtemperature trips provide protection over the full range of RCS conditions is described in Chapter 7.0. Figure 15.0-1 presents allowable reactor coolant loop average temperature and for the design power distribution and flow as a function of primary coolant pressure. The boundaries of operation defined by the overpower trip and the overtemperature trip are represented as "protection lines" on this diagram. The protection lines are drawn to include all adverse instrumentation and setpoint errors so that under nominal conditions a trip would occur well within the area bounded by these lines. The utility of this diagram is in the fact that the limit imposed by any given DNBR can be represented as a line. The DNB lines represent the locus of conditions for which the DNBR equals the safety analysis limit. All points below and to the left of a DNB line for a given pressure have a DNBR greater than the safety analysis limit. The diagram shows that DNB is prevented for all cases if the area enclosed with the maximum protection lines is not traversed by the applicable DNBR line at any point. The difference between the safety analysis trip setpoint assumed for the
analysis and the nominal trip setpoint represents an allowance for
instrumentation channel error. Nominal trip setpoints are specified in the
plant Technical Specifications Bases. During plant startup tests, it was demonstrated that actual instrument time delays are equal to or less than the
assumed values. Additionally, protection system channels are calibrated and
instrument response times determined periodically in accordance with the plant
Technical Specifications.
15.0.7 INSTRUMENTATION DRIFT AND CALORIMETRIC ERRORS -
POWER RANGE NEUTRON FLUX
The instrumentation drift and calorimetric errors used in establishing the
power range high neutron flux setpoint are presented in Table 15.0-5. The calorimetric error is the error assumed in the determination of core
thermal power, as obtained from secondary plant measurements. The total ion
chamber current (sum of the top and bottom sections) is calibrated (set equal)
to this measured power on a periodic basis.
Two options are available for indication of secondary power. These are (1) a
feedwater calorimetric or (2) a steam flow calorimetric. The feedwater
calorimetric uses feedwater flow (feedwater venturi differential pressure), feedwater inlet temperature to the steam generators, and steam pressure (from
which feedwater pressure is inferred). The steam flow calorimetric uses the
same inputs but uses the pressure drop across the steam generator orifice
instead of the feedwater flow. This pressure drop value is normalized to a
precision feedwater flow measurement at the beginning of the cycle. High
accuracy instruments provided measurements with accuracy tolerances much tighter than those which are required to normally control feedwater flow.
15.0-11 Rev. 25 WOLF CREEK 15.0.8 MAJOR PLANT SYSTEMS AND EQUIPMENT AVAILABLE FOR MITIGATION OF TRANSIENT
AND ACCIDENT CONDIITONS
The plant is designed to afford protection against the possible effects of natural phenomena, postulated environmental conditions, and dynamic effects of
the postulated accidents. In addition, the design incorporates features which
minimize the probability and effects of fires and explosions. Chapter 17.0
discusses the quality assurance program which has been implemented to assure
that the NSSS will satisfactorily perform its assigned safety functions. The
incorporation of these features in the plant, coupled with the reliability of
the design, ensures that the normally operating systems and equipment listed in
Table 15.0-6 are available for mitigation of the events discussed in Chapter
15.0. In determining which systems are necessary to mitigate the effects of
these postulated events, the classification system of ANSI-N18.2-1973 is utilized. The design of "systems important to safety" (including protection systems) is consistent with IEEE Standard 379-1972 and Regulatory Guide 1.53, in the application of the single failure criterion.
In the analysis of the Chapter 15.0 events, control system action is considered
only if that action results in more severe accident results. No credit is
taken for control system operation if that operation mitigates the results of
an accident. For some accidents, the analysis is performed both with and
without control system operation to determine the worst case. The pressurizer
heaters are not assumed to be energized during any of the Chapter 15.0 events.
15.0.9 FISSION PRODUCT INVENTORIES
15.0.9.1 Activities in the Core The calculation of the core iodine fission product inventory is consistent with
the inventories given in TID-14844 (Ref. 1) and is based on a core power level
of 3565 MWt. The fission product inventories for other isotopes that are important from a health hazards point of view are consistent with the data from
APED-5398 (Ref. 2). These inventories are given in Table 15A-3. The isotopes
included in Table 15A-3 (Appendix 15A) are the isotopes controlling from
considerations of inhalation dose (iodines) and from direct dose due to
immersion (noble gases).
The isotopic yields used in the calculations are from the data of APED-5398, utilizing the isotopic yield data for thermal fissioning of uranium-235 as the
sole fissioning source. The change in fission product inventory resulting from
the fissioning of other fissionable atoms has been reviewed. The results of this review indicated that inclusion of all fission source data would result in small (less than 10 percent) change in the isotopic inventories.
15.0.9.2 Activities in the Fuel Pellet Clad Gap The fuel-clad gap activities are determined, using the model given in
Regulatory Guide 1.77. Thus, the amount of activity accumulated in the fuel
clad gap is assumed to be 10 percent of the core activity for all isotopes except for Kr-85. For Kr-85 it is assumed to be 30 percent of the core
activity. The gap activities are given in Table 15A-3.
15.0-12 Rev. 25 WOLF CREEK 15.0.10 RESIDUAL DECAY HEAT15.0.10.1 Total Residual Heat Residual heat in a subcritical core is calculated for the LOCA per the requirements of Appendix K of 10 CFR 50.46, as described in References 3 and 4.
These requirements include assuming infinite irradiation time before the core
goes subcritical to determine fission product decay energy. For all other accidents, the same models are used, except that fission product decay energy is based on core average exposure at the end of the equilibrium cycle.15.0.10.2 Distribution of Decay Heat Following Loss-of-Coolant Accident During a LOCA, the core is rapidly shut down by void formation or RCCA insertion, or both, and a large fraction of the heat generation to be considered comes from fission product decay gamma rays. This heat is not distributed in the same manner as steady state fission power. Local peaking effects which are important for the neutron dependent part of the heat generation do not apply to the gamma ray contribution. The steady state factor of 97.4 percent, which represents the fraction of heat generated within the
clad and pellet, drops to 95 percent for the hot rod in a LOCA. For example, consider the transient resulting from the postulated double ended break of the largest reactor coolant system pipe; 1/2 second after the rupture
about 30 percent of the heat generated in the fuel rods is from gamma ray absorption. The gamma power shape is less peaked than the steady state fission power shape, reducing the energy deposited in the hot rod at the expense of adjacent colder rods. A conservative estimate of this effect is a reduction of 10 percent of the gamma ray contribution or 3 percent of the total. Since the water density is considerably reduced at this time, an average of 98 percent of the available heat is deposited in the fuel rods, the remaining 2 percent being absorbed by water, thimbles, sleeves, and grids. The net effect is a factor of 0.95, rather than 0.974, to be applied to the heat production in the hot rod. 15.0.11 COMPUTER CODES UTILIZED
Summaries of some of the principal computer codes used in transient analyses are given below. Other codes, in particular very specialized codes in which the modeling has been developed to15.0-13Rev. 0 WOLF CREEK simulate one given accident, such as those used in the analysis of the reactor coolant system pipe rupture (see Section 15.6), are summarized in their
respective accident analyses sections. The codes used in the analyses of each
transient have been listed in Table 15.0-2.15.0.11.1 FACTRAN FACTRAN calculates the transient temperature distribution in a cross section of a metal clad UO 2 fuel rod and the transient heat flux at the surface of the clad, using as input the nuclear power and the time-dependent coolant parameters (pressure, flow, temperature, and density). The code uses a fuel model which simultaneously exhibits the following features:
- a. A sufficiently large number of radial space increments to handle fast transients such as rod ejection
accidents.
- b. Material properties which are functions of temperature and a sophisticated fuel-to-clad gap heat transfer calculation.
- c. The necessary calculations to handle post-DNB transients: film boiling heat transfer correlations, zircaloy-water reaction, and partial melting of the materials.
FACTRAN is further discussed in Reference 5. 15.0.11.2 LOFTRAN The LOFTRAN program is used for studies of transient response of a PWR system to specified perturbations in process parameters. LOFTRAN simulates a multiloop
system by a model containing reactor vessel, hot and cold leg piping, steam generator (tube and shell sides), and the pressurizer. The pressurizer heaters, spray, relief, and safety valves are also considered in the program. Point model neutron kinetics and reactivity effects of the moderator, fuel, boron, and rods are included. The secondary side of the steam generator utilizes a homogeneous, saturated mixture for the thermal transients and a water level correlation for indication and control. The reactor protection system is simulated to include reactor trips on high neutron flux, overtemperatureT, overpower T, high and low pressure, low flow, and high pressurizer level. Control systems are also simulated, including rod control, steam dump, feedwater control, and pressurizer pressure control. The emergency
core cooling system, including the accumulators, is also modeled.15.0-14Rev. 0 WOLF CREEK LOFTRAN is a versatile program, which is suited to both accident evaluation and
control studies as well as parameter sizing.
LOFTRAN also has the capability of calculating the transient value of DNBR, based on the input from the core limits illustrated on Figure 15.0-1. The core
limits represent the minimum value of DNBR, as calculated for typical or
thimble cell.
LOFTRAN is further discussed in Reference 6.
15.0.11.3 PARAGON/NEXUS PARAGON is based on collision probability - interface current cell coupling methods. PARAGON provides flexibility in modeling including exact cell geometry representation, multiple rings and regions within the fuel pin and the moderator cell geometry, and variable cell pitch. The solution method permits flexibility in choosing the quality of the calculation through both increasing the number of regions modeled within the cell and the number of angular current directions tracked at the cell interfaces. The PARAGON cross section library is a 70-group library that is based on the ENDF/B basic nuclear data. The PARAGON qualification library has been improved through the addition of more explicit fission products and fission product chains; however it is designed to employ any number of energy groups. The new NEXUS cross-section generation system uses PARAGON as the lattice code. PARAGON and NEXUS are further described in References 7 and 11. 15.0.11.4 ANC
ANC is a multidimensional nodal analysis program used to predict nuclear
reactor core reactivity and assembly and rod distributions for normal and off-
normal conditions. The code allows for the treatment of enthalpy, xenon, and
Doppler feedback. A high degree of automation has been incorporated into the
code to address fuel depletion, reactivity coefficients, control rod worths for
nonuniform inlet temperature distribution.
ANC is further described in Reference 8.
15.0.11.5 TWINKLE
The TWINKLE program is a multidimensional spatial neutron kinetics code, which
was patterned after steady state codes presently used for reactor core design.
The code uses an implicit finite-difference method to solve the two-group
transient neutron diffusion equations in one, two, and three dimensions. The
code uses six delayed neutron groups, and contains a detailed multiregion fuel-
clad-coolant heat transfer model for calculating pointwise Doppler and
moderator feedback effects. The code handles up to 2,000 spatial points, and
performs its own steady state initialization. Aside from basic cross section
data and thermal-hydraulic parameters, the code accepts as input basic driving
functions, such as inlet temperature, pressure, flow, boron concentration,
15.0-15 Rev. 29 WOLF CREEK control rod motion, and others. Various edits are provided, e.g., channel-wise
power, axial offset, enthalpy, volumetric surge, point-wise power, and fuel
temperatures.
The TWINKLE code is used to predict the kinetic behavior of a reactor for
transients which cause a major perturbation in the spatial neutron flux
distribution.
TWINKLE is further described in Reference 9.
15.0.11.6 APOLLO APOLLO is a two-group, one dimensional neutron diffusion code designed to
characterize the axial behavior of the core during plant operation in
situations where three dimensional analyses would be time consuming and cumbersome. Pertinent uses include evaluation of limiting power shapes and
scoping the adequacy of reactor protection systems in order to maintain margin
to overpower and DNB limits.
APOLLO is further described in Reference 10.
15.0.11.7 RETRAN RETRAN-02 is a thermal-hydraulic systems analysis code employing a one-
dimensional, homogeneous equilibrium mixture thermal-hydraulic model for the
RCS, a point kinetics model for the reactor core, special component and
auxiliary models (ex., pumps, temperature transport, non-equilibrium pressurizer) and control system models. The code computes pertinent plant
transient information including core power level, RCS pressure and temperature.
RETRAN-02 is further described in Reference 12.
RETRAN-3D is the next generation of RETRAN with additional capabilities and more accurate modeling, and is equivalent to RETRAN-02 when operated in the RETRAN-02 mode. RETRAN-3D is further described in Reference 17. 15.0.11.8 VIPRE-01
The core thermal-hydraulic analysis code VIPRE-01 is an open channel code
designed to evaluate DNBR and coolant state for steady state operations and
transients using subchannel analysis.
VIPRE-01 is further described in Reference 13 and Section 4.4.4.5.
15.0.12 LIMITING SINGLE FAILURES
The most limiting single failure as described in Section 3.1 of safety-related
equipment, where one exists, is identified in each analysis description, and
the consequences of this failure are described therein. In some instances, because of redundancy in protection equipment, no single failure which could
adversely affect the consequences of the transient has been identified. The failure assumed in each analysis is listed in Table 15.0-7.
15.0-16 Rev. 25 WOLF CREEK 15.0.13 OPERATOR ACTIONS For most of the events analyzed in Chapter 15.0 the plant will be in a safe and stable hot standby condition following the automatic actuation of reactor trip. This condition will, in fact, be similar to plant conditions following any normal, orderly shutdown of the reactor. At this point, the actions taken by the operator would be no different than normal operating procedures. The exact actions taken, and the time at which these actions would occur, will depend on
what systems are available (e.g., turbine bypass system, main feedwater system, etc.) and the plans for further plant operation. As a minimum, to maintain the
hot stabilized condition, decay heat must be removed via the steam generators. The main feedwater system and the steam dump or atmospheric relief system could be used for this purpose. Alternatively, the auxiliary feedwater system and the steam generator safety valves may be used, both of which are safety grade
systems. Although the auxiliary feed system may be started manually, it will be automatically actuated, if needed, by one of the signals shown on Figure 7.2-1, such as low-low steam generator water level. Also, if the hot standby condition is maintained for an extended period of time (greater than approximately 18 hours), operator action may be required to add boric acid via
the CVCS to compensate for xenon decay and maintain shutdown margin. Where a stabilized condition is reached automatically following a reactor trip and only actions typical of normal operation are required, this has been stated in the text of the Chapter 15.0 events. For several events involving breaks in the reactor coolant system or secondary system piping, additional requirements for operator action are identified. Following the postulated MSLB, a steamline isolation signal will be generated almost immediately, causing the steamline isolation valves to close within a few seconds. If the break is downstream of the isolation valves, all of which
subsequently close, the break will be isolated. If the break is upstream of
the isolation valves, or if one valve fails to close, the break will be
isolated to three steam generators while the affected steam generator will continue to blow down. Only the case in which one steam generator continues to blow down is discussed here, since the break followed by isolation of all steam
generators will terminate the transient. Steam pressure from the steam generators is relieved by the turbine bypasssystem, secondary system atmospheric relief valves, or secondary system safety valves. The operator is instructed to terminate auxiliary feedwater flow to the affected steam generator, as soon as he determines which steam generator is affected. As soon as an indicated water level returns to the pressurizer and pressure is no longer decreasing, the operator is instructed to terminate the
charging pump flow to limit system repressurization. For long-term cooling following a steamline break, the operator is instructed to use the intact steam generators for the purpose of removing decay heat and plant stored energy. This is done by feeding the steam generators with auxiliary feed-water to maintain an indicated water level in the steam generator narrow-range span.15.0-17Rev. 11 WOLF CREEK A safety injection signal (generated a few seconds after the break on low steam line pressure) will cause main feedwater isolation to occur. A steam line
break protection signal (Section 7.3.8.3.2) will also cause main feedwater
isolation to occur. The only source of water available to the affected
generator is then the auxiliary feedwater system. Following steamline
isolation, steam pressure in the steamline with the affected steam generator will continue to fall rapidly, while the pressure stabilizes in the remaining three steam lines. The indication of the different steam pressures will be
available to the operator, within a few seconds of steamline isolation. This
will provide the information necessary to identify the affected steam generator
so that auxiliary feedwater to it can be isolated. Manual controls are provided in the control room for start and stop of the auxiliary feedwater pumps and for the control valves associated with the auxiliary feedwater system. The means for detecting the affected steam generator and isolating
auxiliary feedwater to it requires only the use of safety grade equipment available following the break. The removal of decay heat in the long term (following the initial cooldown), using the remaining steam generators, requires only the auxiliary feedwater system as a water source and the secondary system safety valves to relieve steam. The operator has available, in the control room, an indication of pressurizer water level from the reactor protection system instrumentation. Indicated
water level returns to the pressurizer in approximately 5 to 7 minutes
following the steamline break. To maintain the indicated water level, the
operator can start and stop the charging pumps as necessary. The pressurizer level instrumentation and manual controls for the operation of the charging pumps meet the required standards for safety systems. As indicated, the information for terminating auxiliary feedwater to the affected steam generator is available to the operator within 1 minute of the break, while the information required for terminating the charging/SI flow
becomes available within 5 to 7 minutes following the break. The requirements to terminate auxiliary feedwater flow to the affected steam generator can be
met by switch actions by the operators, i.e., closing auxiliary feed discharge
valve. Thus, the required actions to limit the cooldown can be recognized, planned, and performed within 10 minutes. After it is determined that the
pressurizer level is restored and SI flow is no longer required, normal
charging flow is established and the SI flow is eventually terminated to
prevent repressurization of the RCS. For decay heat removal and plant
cooldown, the operator has a considerably longer time period in which to
respond because of the large initial cooldown associated with a steamline break
transient. For a feedwater line break, the required operator actions and times are discussed in Section 15.2.8 and Table 15.2-1. Auxiliary feedwater flow is
initiated automatically, as is safety injection. As in the steamline break, the operator terminates auxiliary feedwater flow to the affected steam
generator as soon as he determines which unit is affected, using safety grade
equipment. Where possible, the operator should also increase auxiliary
feedwater flow to the intact steam generators in order to shorten the time
until primary temperatures begin to decrease. The analysis presented in Section
15.2.8 assumes a 30-minute delay until these actions occur.15.0-18Rev. 10 WOLF CREEK As soon as primary temperature begins to decrease, the operator can use the steam dump system or the steam generator atmospheric relief valves to begin a
controlled cooldown. In addition, if the U-tubes of the intact steam
generators are covered with water as indicated by post accident monitoring
system (PAMS) steam generator water level instrumentation (see Chapter 7.0), the operator can modulate the high-head charging pumps, so that the primary pressure decreases while ensuring that voiding does not occur within the RCS. The primary pressure-temperature relationship can be monitored by the operator
via the PAMS widerange RCS pressure and temperature instruments. Using the above-mentioned PAMS indications, the operator can maintain the plant in a hot shutdown condition for an extended period of time, or can proceed to a
cold shutdown condition as desired. The safety-related indicators for steamline pressure and pressurizer water level noted above are further discussed in Section 7.5. Tables 15.0-8 and 15.0-9 list the short term operator actions required to bring the plant to a stable condition for the LOCA and steam generator tube rupture (SGTR). Further information (including alarms which alert the operator) on operator action for these two accidents are given in Section 6.3.2.8 for the LOCA and Section 15.6.3 for the SGTR. Process information available to the operator in the control room following either of these accidents (LOCA or SGTR) is given in Section 7.5. Instrumentation and controls provided to allow the operator to complete required manual actions are classified as Class IE. Electrical components are also classified as Class IE. Mechanical components are classified as Safety Class 1, 2, or 3. Safety systems required for accident mitigation are designed to function after the occurrence of the worst postulated single failure. There are no adverse
impacts as a result of these actions. 15.0.14 REFERENCES
- 1. DiNunno, J. J., et al., "Calculation of Distance Factors for Power and Test Reactor Sites," TID-14844, March 1962.
- 2. Meek, M. E. and Rider, B. F., "Summary of Fission Product Yields for U-235, U-238, Pu-239, and Pu-241 at
Thermal Fission Spectrum and 14 Mev Neutron Energies," APED-5398, March 1968.
- 3. Bordelon, F. M., et al., "SATAN-VI Program:
Comprehensive Space-Time Dependent Analysis of Loss-of-
Coolant," WCAP-8302 (Proprietary) and WCAP-8306 (Non-Proprietary), June 1974.15.0-19Rev. 10 WOLF CREEK
- 4. Bordelon, F. M., et al., "LOCTA-IV Program: Loss-of-
Coolant Transient Analysis," WCAP-8301 (Proprietary) and
WCAP-8305 (Non-Proprietary), June 1974.
- 5. Hargrove, H. G., "FACTRAN - A FORTRAN-IV Code for
Thermal Transients in a UO 2 Fuel Rod," WCAP-7908-A dated December, 1989.
- 6. Burnett, T. W. T., et al., "LOFTRAN Code Description,"
WCAP-7907-A, April 1984.
- 7. Slagle, W. H., "Qualification of the Two-Dimensional Transport Code PARAGON", WCAP-16045-P-A, September 2004.
- 8. Liu, Y. S., et al., "ANC A Westinghouse Advanced Nodal Computer
Code," WCAP-10965, 1985
- 9. Risher, D. H., Jr. and Barry, R. F., "TWINKLE - A Multi-
Dimensional Neutron Kinetics Computer Code," WCAP-7979-
P-A (Proprietary) and WCAP-8028-A (Non-Proprietary), January 1975.
- 10. Mayhue, L. T. And Yarbrough, M. B., "APOLLO A One Dimensional Neutron
Diffusion Theory Program," WCAP-13524, October 1992.
- 11. Huria, H., "Qualification of the NEXUS Nuclear Data Methodology", WCAP-16045-P-A Addendum 1, November 2005.
- 12. McFadden, J. H., et al. "RETRAN A Program for Transient Thermal
Hydraulic Analysis of Complex Fluid Flow Systems," EPRI-NP-1850-CCM-
A, October 1984.
- 13. "VIPRE-01: A Thermal-Hydraulic Code for Reactor Core," Battelle,
Pacific Northwest Laboratories, Richland, Washington, EPRI NP-2511-
CCM-A, August 1987.
- 14. Friedland, A. J., Ray, S., "Revised Thermal Design Procedure,"
WCAP-11397-P-A, April, 1989.
- 15. Deleted
- 16. WCAP-10444-P-A, "Reference Core Report - Vantage 5 Fuel
Assembly", S. L. Davidson, Ed., Westinghouse, December 1983.
- 17. Paulsen, M. P., et al. "RETRAN-3D - A Program for Transient Thermal Hydraulic Analysis of Complex Fluid Flow Systems," EPRI-NP-7450(A),
July 2001.
15.0-20 Rev. 29 WOLF CREEK TABLE 15.0-1 NUCLEAR STEAM SUPPLY SYSTEM POWER RATINGSNSSS thermal power output, MWt3,579Nominal thermal power generated by the reactor coolant14 pumps, MWtRated reactor core thermal power output, MWt3,565 Rev. 7 WOLF CREEK TABLE 15.0-2
SUMMARY
OF INITIAL CONDITIONS AND COMPUTER CODES USED Reactivity Coefficients (a) Assumed Initial NSSS
Moderator Thermal Power Output
Computer Density Assumed (b)
Faults Codes Utilized /Temp Coeff Doppler (MWt)
15.1 Increase in heat removal by
the secondary system
Feedwater system malfunctions RETRAN, VIPRE 0.43 k/gm/cc Lower (a) 0 and 3,565 that result in an increase in feedwater flow
Excessive increase in LOFTRAN, VIPRE Figure 15.0-6 Lower (a) 3,565
secondary steam flow and 0.43
Inadvertent opening of a RETRAN, VIPRE Function of See Section 0
steam generator atmospheric moderator density 15.1.5 (Subcritical) relief or safety valve (see Section 15.1.4, Figure
15.1-11)
Steam system piping failure RETRAN, VIPRE Function of See Section 0
moderator density 15.1.5 (Subcritical)
(see Section
15.1.5, Figure
15.1-11)
15.2 Decrease in heat removal
by the secondary system
Loss of external electrical RETRAN, VIPRE +7 pcm/°F Lower and 3,565
load and/or turbine trip upper (a)
Rev. 13 WOLF CREEK TABLE 15.0-2 (Sheet 2)
Loss of nonemergency ac RETRAN, VIPRE +7 pcm/°F Upper (a) 3,565
power to the station
auxiliaries
Loss of normal feedwater flow RETRAN, VIPRE +7 pcm/°F Upper (a) 3,565
Feedwater system pipe break RETRAN, VIPRE +7 pcm/°F Lower (a) 3,565
15.3 Decrease in reactor coolant
system flow rate
Partial and complete loss RETRAN, VIPRE +7.0 pcm/°F Upper (a) 3,565
of forced reactor coolant flow
Reactor coolant pump shaft RETRAN, VIPRE +7.0 pcm/°F Upper (a) 3,565
seizure (locked rotor) FACTRAN
15.4 Reactivity and power
distribution anomalies
Uncontrolled rod cluster TWINKLE, FACTRAN, +7.0 pcm/°F Consistent 0
control assembly bank with- VIPRE with lower
drawal from a subcritical or limit shown
low power startup condition on Figure 15.0-2
Uncontrolled rod cluster con- RETRAN, VIPRE +7.0 pcm/°F Lower and 3,565 trol assembly bank withdrawal and 0.43 gm/cc upper (a) at power
Rod cluster control assembly PARAGON/NEXUS, ANC NA NA 3,565 misalignment Startup of an inactive reactor LOFTRAN, VIPRE 0.43 k/gm/cc Lower (a) 2,495 coolant loop at an incorrect temperature
Chemical and volume control NA NA NA 0 and 3,565
system malfunction that results
in a decrease in the boron
concentration in the reactor
coolant
Rev. 29 WOLF CREEK TABLE 15.0-2 (Sheet 3) Inadvertent loading and opera- ANC, PARGON/NEXUS NA NA 3,565 tion of a fuel asembly in an
improper position
Spectrum of rod cluster control TWINKLE, FACTRAN, Refer to Consistent 0 and 3,565
assembly ejection accidents ANC Section with lower
15.4.8 (c) limit shown
on Figure 15.0-2
15.5 Increase in reactor coolant
inventory
Inadvertent operation of the RETRAN, VIPRE +7.0 pcm/°F Lower (a) 3,565
ECCS during power operation
Chemical and volume LOFTRAN 0.43 k/gm/cc Lower and 3,565 control system malfunction and +7.0 pcm/°F Upper (a) that increases reactor coolant inventory
15.6 Decrease in reactor coolant
inventory
Inadvertent opening of a RETRAN, VIPRE 0.43 k/gm/cc Upper (a) 3,565 pressurizer safety or relief and +7.0 pcm/F valve
Steam generator tube rupture RETRAN NA NA 3,565
Loss-of-coolant accidents SB LOCA: NOTRUMP, See Section See Section 3,565 resulting from the spectrum LOCTA-IV. LB LOCA: 15.6.5 15.6.5, of postulated piping breaks SATAN-VI, WREFLOOD references (c) references within the reactor coolant COCO, BASH, pressure boundary LOCBART
(a) See Figure 15.0-2. (b) A minimum of 2 percent margin is applied to the values shown for analysis purposes. (c) The moderator density coefficients for these accidents were translated into moderator temperature
coefficients.
Rev. 29
WOLF CREEK TABLE 15.0-3 NOMINAL VALUES OF PERTINENT PLANT PARAMETERS UTILIZED IN THE ACCIDENT ANALYSES
- Thermal output of NSSS, MWt See Table 15.0-2 Core inlet temperature, °F 555.8 Vessel average temperature, °F 588.4 Reactor coolant system pressure, psia 2,250 Reactor coolant flow per loop, gpm 90,324
Steam flow from NSSS, Mlb/hr 15.92 Steam pressure at steam generator outlet, 944 psia Maximum steam moisture content, % 0.25
Assumed feedwater temperature at steam 446 generator inlet, °F Average core heat flux, Btu/hr-ft 2 198340 Steam generator tube plugging, % 10.0
- Steady-state errors discussed in Section 15.0.3.2 are added to these values to obtain initial conditions for transient analyses
except where discussed otherwise. Rev. 13 WOLF CREEK TABLE 15.0-4 TRIP POINTS AND TIME DELAYS TO TRIP ASSUMED IN ACCIDENT ANALYSES
Limiting Trip
Trip Point Assumed Time Delays
Function In Analyses (Seconds) Power range high neutron
flux, high setting 118% 0.5
Power range high neutron
flux, low setting 35% 0.5
High neutron flux, P-8 84% 0.5
Overtemperature T Variable see 6.0* Figure 15.0-1 Overpower T Variable see 6 0* Figure 15.0-1
High pressurizer pressure 2,460 psia 2.0
Low pressurizer pressure 1925 psia 2.0
Low reactor coolant flow 87 % loop flow 1.0 (from loop flow detectors)
Undervoltage trip 10308 VAC 1.5
Turbine trip Not applicable 2.0
Low-low steam generator 0% of narrow 2.0
level range level span
High steam generator level, 100% of narrow 2.0 trip of the feedwater pumps** range level span and closure of feedwater
system valves, and turbine
trip***
- Total time delay (including scoop delay and thermal lag, combined
RTD/thermowell response, and trip circuit channel electronics delay)
from the time the temperature difference in the coolant loop exceeds
the trip setpoint until the rods are free to fall.
- Not part of primary success path for accident mitigation.
- No direct credit is taken for the turbine trip function in the accident analyses.
- Not part of primary success path for accident mitigation.
Rev. 27
WOLF CREEK TABLE 15.0-5 DETERMINATION OF MAXIMUM OVERPOWER TRIP POINT - POWER RANGE NEUTRON FLUX CHANNEL - BASED ON NOMINAL SETPOINT
CONSIDERING INHERENT INSTRUMENTATION ERRORS Nominal setpoint (% of rated power) 109 Calorimetric errors in the measurement of secondary system thermal power: Estimated Accuracy of Effect on
Measurement Thermal Power
of Variable Determination
Variable (% error)
(% error)
Assumed calorimetric error 2 (a)* (% of rated power for both feedwater calorimetric and steam flow calorimetric measurements) Axial power distribution effects on total ion
chamber current Estimated error (% of 3 rated power) Assumed error (% of 5 (b)* rated power) Instrumentation channel drift and setpoint
reproducibility Estimated error (% of 1 rated power) Rev. 11 WOLF CREEK TABLE 15.0-5 (Sheet 2) Estimated Accuracy of Effect on
Measurement Thermal Power of Variable Determination Variable (% error)
(% error)
Assumed error (% of 2 (c)* rated power)
- Total assumed error in setpoint (% of rated
power)
(a) + (b) + (c) +9 Maximum overpower trip point, assuming all
individual errors are simultaneously in the most adverse direction (% of
rated power) 118 Rev. 0 WOLF CREEK TABLE 15.0-6 MAJOR PLANT SYSTEMS AND EQUIPMENT AVAILABLE FOR MITIGATION OF TRANSIENT AND ACCIDENT CONDITIONS Incident Reactor Trip Functions ESF Actuation Functions Other Equipment ESF Equipment15.1Increase in heat---- removal by the secondary systemFeedwater sys-Source range high flux, High-high SG levelFeedwater isolation-tem malfunctionsintermediate range high flux, produced feedwater valvesthat result inpower range high flux, low-isolation and turbine tripan increase inlow steam generator level, feedwater flow manual overpower T, over-temperatureT, turbine tripExcessivePower range high flux, over--Pressurizer safety -increase in temperatureT, overpower valves, steam generator secondaryT, manual safety valves steam flow InadvertentManual, SIS, power rangeLow pressurizer pressure,Feedwater isolation Auxiliary feedwater opening of a high flux, overpower Tlow compensated steamvalves, steam line system, safety steam generator line pressure high negative isolation valves injection system atmospheric relief or steam pressure rate safety valveSteam systemPower range high flux,Low pressurizer pressure,Feedwater isolationAuxiliary feedwaterpiping failurepressure, manual, SISlow compensated steam linevalves, steam linesystem, safety overpowerTpressure, hi-1 containmentisolation valvesinjection system pressure, hi-2 containment pressure, high negative steam pressure rate, SIS, high-high SG level, low-low SG level, manual15.2Decrease in---- heat removal by the secondary
systemLoss of ex-Low-low SG level, turbine Low-low SG level, manual Pressurizer safety -ternal load/ trip, high pressurizer valves, steam generatorturbine trippressure, overtemperature safety valvesT, manual high pressurizer water level Rev. 13 WOLF CREEK TABLE 15.0-6 (Sheet 2) Incident Reactor Trip Functions ESF Actuation Functions Other Equipment ESF EquipmentLoss of non-Manual, low-low SG level, Low-low SG level, loss ofSteam generator safetyAuxiliaryemergency aclow flow offsite power, manual valves, pressurizer feedwater system power to the safety valves station auxil-iariesLoss of normalLow-low SG level, manual, Low-low SG level, loss of Steam generator safety Auxiliary feedwater feedwater flow overtemperatureT offsite power, manual valves, pressurizer system safety valvesFeedwaterLow-low SG level, highHi-1 containment pressure,Steam line isolationAuxiliary feedwatersystem pipepressurizer pressure, SIS, low-low SG level, lowvalves, feedlinesystem, safety break manual, overtemperature T compensated steam lineisolation, pressurizerinjection system pressure SIS, loss of offsite safety valves, steam power, manual generator safety valves15.3Decrease in---- reactor coolant system flow ratePartial and,Low flow, undervoltage-Pressurizer safety -complete lossunderfrequency, manualvalves of forced reac-
tor coolant flowReactor cool-Low flow, high pres--Pressurizer safety-ant pump shaftsurizer pressure, manualvalves, steam
seizure (locked generator safety valves rotor)15.4Reactivity and---- power distribution
anomaliesUncontrolledSource range high flux,---rod clusterintermediate range high flux,controlpower range high flux (high assembly bank setpoint), power range highwithdrawal fromflux (low setpoint), manual, a subcritical or power range high flux rate low power start-up condition Rev. 13 WOLF CREEK TABLE 15.0-6 (Sheet 3) Incident Reactor Trip Functions ESF Actuation Functions Other Equipment ESF Equipment Uncontrolled Power range high flux, - Pressurizer safety - rod cluster overtemperature T, high valves,steam generator control pressurizer pressure, manual, safety valves assembly bank high pressurizer water level, withdrawal at overpower T, power range power high positive flux rate Rod cluster Power range negative - - - control flux rate, overtemperature assebmly mis- T, manual alignment Startup of an Manual, power range high flux - Low insertion limit - inactive reac- above P8 setpoint with low annun-ciators for tor coolant flow boration loop at an in-correct temperature Chemical and Power range high flux, over- - Pressurizer safety - volume control, temperature T, manual, over- valves, steam generator system mal-power T high pressurizer safety valves rod function that pressure, high pressurizer insertion limit alarms, results in a water level position step counter, decrease in RT alarm, audible count boron rate from BF3 detector concentrattion source range high flux in the reactor alarm coolant Spectrum of Source range high flux, Low pressurizer pressure, Pressurizer safety ESFAS rod cluster con- intermediate range high flux, Hi-1 containment pressure, valves trol assembly power range high flux, Hi-3 containment pressure, (RCCA) ejection high positive flux rate, manual. accidents manual 15.5 Increase in
- - - - reactor coolant inventory Inadvertent Low pressurizer - - Safety injection operation of pressure, manual, system the ECCS dur-safety injection trip ing power oper-tion
Rev. 25 WOLF CREEK TABLE 15.0-6 (Sheet 4) Incident Reactor Trip Functions ESF Actuation Functions Other Equipment ESF Equipment 15.6 Decrease in - - - - reactor coolant inventory Inadvertent Low pressurizer Low pressurizer pressure, - Safety injection opening of a pressure, overtemperature manual system
pressurizer, T, manual safety or relief valve Steam generator Low pressurizer pressure, Low pressurizer pressure Essential service water Emergency core tube rupture SIS, manual, manual system, component cooling cooling system, overtemperaturerT water system, steam auxiliary feed- generator shell side water system, fluid operating system, emergency power steam generator safety system containment and/or atmospheric relief isolation valves, steam line isolation valves Loss of coolant Pressurizer low pressure, Hi-1 containment pressure, Essential service water Emergency core accidents SIS, manual low pressurizer pressure system, component cooling cooling system, resulting from Hi-3 containment pressure, water system, steam gen- auxiliary feedwater the spectrum of manual erator safety and/or system, containment postulated AFAS on loss of offsite atmospheric relief valves heat removal piping breaks power system, emergency within the power system reactor coolant containment pressure isolation boundary R ev. 15 WOLFCREEKTABLE15.0-7SINGLEFAILURESASSUMEDINACCIDENTANALYSESEventDescriptionWorstFailureAssumedFeedwatertemperaturereduction(1)ExcessivefeedwaterflowOneprotectiontrainExcessivesteamflow(1)InadvertentsecondarydepressurizationOnesafetyinjectiontrainSteamsystempipingfailureOnesafetyinjectiontrainSteampressureregulatormalfunction(2) LossofexternalloadOneprotectiontrain TurbinetripOneprotectiontrain InadvertentclosureofMSIVOneprotectiontrain LossofcondenservacuumOneprotectiontrain LossofacpowerOneauxiliaryfeedwaterpumpLossofnormalfeedwaterOneauxiliaryfeedwaterpumpFeedwatersystempipebreakOneprotectiontrain PartiallossofforcedreactorcoolantOneprotectiontrain flowCompletelossofforcedreactorcoolantOneprotectiontrain flowRCPlockedrotorOneprotectiontrainRCPshaftbreakOneprotectiontrain RCCAbankwithdrawalfromsubcriticalOneprotectiontrain RCCAbankwithdrawalatpowerOneprotectiontrainDroppedRCCA,droppedRCCAbankOnenuclearinstrumentationsystemchannelStaticallymisalignedRCCA(3) SingleRCCAwithdrawalOneprotectiontrain InactiveRCpumpstartupOneprotectiontrain Flowcontrollermalfunction(2) UncontrolledborondilutionStandbychargingpumpisoperating(4)Improperfuelloading(3)RCCAejectionOneprotectiontrainInadvertentECCSoperationatpowerOneprotectiontrainIncreaseinRCSinventoryOneprotectiontrainBWRtransients(2)InadvertentRCSdepressurizationOneprotectiontrain Failureofsmalllinescarryingprimary(3)coolantoutsidecontainmentSteamGeneratorTubeRuptureAFWflowcontrolvalvetorupturedSGfailsopenFuelHandlingAccident(3) BWRpipingfailures(2)SpectrumofLOCASmallbreaksOnesafetyinjectiontrain LargebreaksOneRHRpumpNOTES:(1)Noprotectionactionrequired(2)NotapplicabletoWCGS(3)Notransientanalysisinvolved(4)Appliestopowerandstartupoperationsonly.AsinglefailureintheVCTlevelcontrollerwhichresultsinthecontinuationofthedilutionflow,evenafterthe"stopautomakeup"setpointisexceeded,isassumedforMode3,4and5.Rev.14 WOLF CREEK TABLE 15.0-8 OPERATOR ACTIONS (1) REQUIRED FOR SMALL AND LARGE LOCAS Time Operator Action Reactor trip signal is None actuated (2)Safety injection signal None is actuated (2)Prior to generation of Reset safeguards actuation signal. RWST low level signal Check sump water level indicator. Generation of RWST low Verify completion of automatic switch-level signal over to ensure components have been
properly realigned. Perform the additional valve
alignments required for switchover to recirculation (3).Switchover to cold leg Perform operations necessary to switch injection plus 10 hours to simultaneous hot and cold leg recirculation. To final stabilized Monitor system pressure and tempera-condition ture. Control pressurizer water level with safety injection system. (1) Actions associated with primary system protection. (2) These times can be found in the sequence of events tables
in Section 15.6.5.
(3) See Section 6.3.2.8 for the manual actions required for com-
pletion of switchover. Operator actions associated with
containment protection is discussed in Section 6.2. Rev. 13 WOLF CREEK TABLE 15.0-9
SHORT TERM OPERATOR ACTIONS REQUIRED FOR STEAM GENERATOR TUBE RUPTURE Time System Operator ActionReactor trip signalReactor trip systemNone
actuatedSafety injection signalSafety injection systemNone actuatedPost SI signal generationSafety injection system,Perform operator actions necessary to to plant stabilizationauxiliary feedwater system,isolate the ruptured steam generator.steam dump system[Isolate steam flow from and feed flow to the ruptured steam generator] Reduce RCS temperature to increase RCS subcooling. Depressurize RCS to equili-brate RCS and ruptured steam generator pressure. Terminate SI, establish normal charging/letdown flow. Proceed with normal plant cooldown, while monitoring reactor coolant system pressure, temperature, and boron concentration. Rev. 13
- *
- 80 r----------------------------------------------------, **. ** .. .. ***** ... *. *. * .. ** .. **. *. 40 570 580 590 600 610 620 630 Vessel Average Temperature (DEG-F) WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.0-1 Illustration of Overtemperature and Overpower AT Protection Rev. 10
- 0 2 4 6 8 10 12 14 16 18 20020406080100 FIGURE 15.0-2 DOPPLER POWER COEFFICIENT USED IN ACCIDENT ANALYSIS WOLF CREEK UPDATED SAFETY ANALYSIS REPORT Rev. 15 PERCENT POWERD, PCM PER PERCENT POWER
NOTE 1 - "UPPER CURVE" MOST NEGATIVE DOPPLER ONLY POWER DEFECT = - 1.6 % K (0 TO 100% POWER)
NOTE 2 - "LOWER CURVE" LEAST NEGATIVE DOPPLER ONLY POWER DEFECT = - 0.84 % K (0 TO 100% POWER) NOTE 1 NOTE 2 N -. U) . *,..... .1--0 * .. '::J" a.. ::c (I) <") 0
- u.. 0 a.. N 0 . .... 0 ....
- W* X --* --*--------*
__ .;___. -----. 0 o;* GO ,.... U) 1.0 '::J" <") . . . . . 0 0 0 0 0 0 0 N. 0 0 =: 0 .... <") a.. 0 0 ffi 0 N 0 0 ..... a:: 0 z: 00 . 0 {!OdHSVO dOl 01 NOiliSOd . WOL!' CREEK Rev. 0
- UPDATED SUBTY.ANALYSIS REPORT FIGURE 15.0-3 RCCA POSITION VERSUS TIME . To DASHPOT '
1.0 0.9 0.8 :z: 0.7 1-a::: 0 lr: >-0.6 1-> 1-0.5 (..) LU a::: Q LU N _, :z: 0.3 a::: 0 z: 0.2 0.1 o.o 0.00 0.20 Rev. 0 CREEK 0.60 0.80 1.00 ROO POSITION (FRACTION INSERTED) WOL!' CREEK UPDATED SA!'ETY ANALYSIS REPORT FIGURE 15.0-4 NORMALIZED Roo WORTH VERSUS PERCENT INSERTED
- . ; * .. *
- .: ..
- .. I .... .: .. ... )-, .. .. '-{ CREEK I. I .. ) I !** .. *.* _. :"**< 1 1.0 I *. 0.9 I I l 0.8 '1 .* . ' X: 1-1-0 . 0.7 I 3: >-1-'_. ., > -J 1-0.6 (,) """ J I UJ 0::: """ (,) (,) 0::: 0 UJ N _, i " I 0::: *o z I ., I I "' I " I 0.1 1*-0.0 o.o 0.2 0.6 0.8 1.0 1.2 NORMALIZED TIME AFTER DROP BEGIN ROO DROPPED TIME TIME TO OASHPOT ; WOLI!' CREE&: **oPDA'l'ED SAPETY ANALYSIS REPORT Rev. 0 I..* FIGURE* 15.0-5 NoRMALIZED RCCA BANK REACTIVITY WORTH VERSUS .. NORt1Al1Z:ED DROP TIME
.. *.**, 0 . 0 (. *-' f I ,.-1.'. 0 0 0 0 N I 0 *. % UJ 1-* .. Cl) CI) 1-z _, 0 0 <..) a: 0 <.) UJ. a:: ooJw5Jdv !N3101:H300 Al1SN30 MO!VM300H WOL!'CRBBK OPDA'l'ED SAI!'B'l'Y AltALYSIS.REPOH Rev. 0 FIGURE 15.0-6 MINIMUM MOOERATOR DENSITY . CO£F.f.l.CI£NT USED ,lN ANALYSIS ' ' ....... *: *.'. '.'
- *
- AFWS eves ESFAS FW RTS SIS SI RT cs ESF ECCS NOTES; WOLF CREEK ABBREVIATIONS USED: -AUXILIARY FEEDWATER SYSTEM -CHEMICAL AND VOLUME CONTROL SYSTEM -ENGINEERED SAFETY FEATURES ACTUATION SYSTEM -FEEDWATER
-REACTOR TRIP SYSTEM -SAFETY INJECTION SYSTEM -SAFETY INJECTION -REACTOR TRIP -CONTIANMENT SPRAY -ENGINEERED SAFETY FEATURE -EMERGENCY CORE COOLING SYSTEM HL CL ccws RCS ESWS HPI LPI CI SG GWPS -HOT LEG -COLD LEG -COMPONENT COOLING WATER SYSTEM -REACTOR COOLANT SYSTEM -ESSENTIAL SERVICE WATER SYSTEM -HIGH PRESSURE INJECTION -LOW PRESSURE INJECTION -CONTAINMENT ISOLATION -STEAM GENERATOR -GASEOUS WASTE PROCESSING SYSTEM 1. FOR TRIP INITIATION AND SAFETY SYSTEM ACTUATION. MULTIPLE SIGNALS ARE SHOWN BUT ONLY A SINGLE SIGNAL IS REQUIRED. THE OTHER SIGNALS ARE BACKUPS. 2. NO TIMING SEQUENCE IS IMPLIED BY POSITION OF VARIOUS BRANCHES. REFER TO EVENT TIMING SEQUENCES PRESENTED IN TABULAR FORM IN PERTINENT ACCIDENT ANALYSIS SECTION OF CHAPTER 15.0 OF THE FSAR. DIAGRAM SYMBOLS: C, _____ .J) -EVENT TITLE 0 -BRANCH POINT FOR DIFFERENT PLANT CONDITIONS -SAFETY SYSTEM < > -SAFETY ACTION -SYSTEM REQUIRED TO MEET SINGLE-FAILURE CRITERIA 1-; \ -MANUAL ACTION REQUIRED DURING SYSTEM OPERATION \ ) -WOLFCREEK Rev.13 UPDATED SAFETY ANALYSIS REPORT FIGURE 15.0 7 ABBREVIATIONS AND SYMBOLS USED IN SEQUENCE DIAGRAMS HIGH NEUTRON FLUX 1/2 SOURCE RANGE* HIGH NEUTRON FLUX 1/2 INTERMEDIATE RANGE HIGH NEUTRON FLUX 2/4. POWER RANGE OVERPOWER 2/lt LOW-LOW SG LEVEL 214 H IN ANY SG
- FOR POWER < P6 WOLF CREEK EXCESSIVE HEAT REMOVAL DUE TO FEEDWATER SYSTEM MALFUNCTIONS POWER< PIO RTS , .. ... ' IS F I \ , ,_ REACTOR TRIP BREAKERS , ;\ 's \ ,' " CONTROL RODS GRAVITY INSERTION PASSiVE CONTROL ROD REACTIVITY CONTROL POWER > PIO RTS ' , ' IS F! ' , ' REACTOR TRIP BREAKERS , ... I ' IS F' '* .. ' CONTROL RODS GRAVITY INSERTION PASSIVE CONTROL ROD REACTIVITY CONTROL
- HIGH NEUTRON FLUX . POWER RANGE OVERPOWER 2N r-OVER TEMPERATURE LOW-LOW SG LEVEL 214 IN ANY SG TURBINE TRIP
- Rev.13 WOLFCREEK UPDATED SAFETY ANAL YSlS REPORT EXCESSIVE HEAT REMOVAL DUE TO FEEDWATER SYSTEMS MALFUNCTION I
OVERPOWER 2N OVERTEMPERATURE 2N HIGH NEUTRON FLUX POWER RANGE y . Rev. 0 w:>LF CREEK ( EXCESSIVE LOAD INCREASE ------r--- RTS , ' :s F' I ' " REACTOR TRIP BREAKERS , .... I S \ t-" "" CONTROL RODS GRAVITY INSERTION PASSIVE CONTROL ROO REACT IV lTV CONTROL J i--fU.LL POwER PRESSURIZER SAFETY VALVES PASSIVE SAFETY VAlVES OPEN TO RELIEVE RCS PRESSURE SG SAFETY VALVES PASS1VE SAFETY VALVES OPEN TO RELIEVE SECONDARY SYSTEM PRESSURE NOTES: I. THIS DIAGRAM APPLIES TO BOTH MANUAL AND AUTOMATIC CONTROL MODES. 2. FOR THIS TRANSIENT. REACTOR PROTECTION SYSTEM FUNCTIONS ARE ASSUMED* TO BE OPERATIVE. BUT A RT IS HOT EXPECTED. WOLP CREEK SA!'BrY RIPORT FIGURE 15.0-9 EXCESSIVE LOAD INCREASE
- a IEUTIGI rLUt * **zt*
hf:iiNI-*. Sl 0 .. .. ,*. I $ f' " ... ,/ ,.ssua lle.:.I .. CGIIJIIIMif 2 IIUUt: uw m*u* .. SIUil II ..._.LOlli' lliiUMttS SullY I Utili* .. 'flOr tO LIIUTIC$ .. SSUI( .... ' flf:S.IlU Lllfl; SU SlCIIGII 7.5 1*1 fGII *IIIOICifGU 1110 I[COIII(IS lllllllll IO.Illl Gf(IUGII fOUIIIIII& 'lilt* (1(11. . llfill*! C011rli114UT 213 *l'tfssua 1.111 STUN l*ll ** 2/J ..... IIGK'I(&olflll Sllolll 2JJ NS$111( Ult II ..._ LOlli' (dll) lOll-lOr IS UYO. II Gil[ S6 -1/Z llll-lOO sa uwu 211i II 21* SQ ITilltiiiE DtiY£1 .PIWS) Sl. SiCI&L I Ioiii IS UY£l II In sa . .. .... .... (
- HIGH PRESSURIZER 2N rl RTS PRESSURE OVERTEMPERATURE 2/14 , ,, : s F I ', I H I GH PRESSUR I ZER 2/14 .. WATER LEVEL
- REACTOR TRIP LOW-LOW SG LEVEL 2/4 BREAKERS IN ANY SG , ... I \ 'tURBINE TRIP \ s F I '* , , CONTROL RODS GRAVITY INSERTION PASSIVE CONTROL ROD
- REACTIVITY CONTROL LOW-LOW SG LEVEL 2N IN ONE SG MANUAL 1/2 "FOR CASE WHERE TURBINE TRIP OCCURS,
- A REACTOR TRIP SIGNAL ON TURBINE TRIP IS ANTICIPATED (FOR POWER > P9) TURBINE TRIP SIGNAL DUE TO: 2/3 LOW TRIP FLUID PRESSURE TURBINE STOP VALVE CLOSURE WOLF CREEK LOSS OF EXTERNAL ELECTRICAL LOAD I POWER ESFAS , .. ' 's \ F' ' , ., AFWS , .. I ' \ S F I '* .. ' FW TO PRESSURIZER SG SAFETY SAFETY VALVES VALVES PASSIVE PASSIVE SAFETY VALVES SAFETY VALVES OPEN TO RELI EVE OPEN TO RELIEVE RCS PRESSURE SECONDARY SYSTEM PRESSURE DELIVER l AUXILIARY CONTROL CORE R 13 HEAT REMOVAL
-* WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.0-11 LOSS OF EXTERNAL LOAD I LOW-LOW SG LEVEl 2/ .. IN ANY LOOP ANTIC I PA ltD RT ON TURBINE TRIP LOW REACTOR COOLANT 2/3 flOW IN ONE LOOP .-c "'D 0 0 CJ) -tOO oo m :i!'TI 0 Ul cnz::!! i!mG> ;:Ho -tS:c -m::O )>0 ZG).- ZAI c:zo >m xo.!.. rm j=-<N -)> c;; --o :::u mo m "'D ::0 0 CD :;o .... " ' 1 S F' \ , ... , REACTOR TRIP BREAKERS CONTROl RODS GRAVITY INSERTIOH PASSIVE CONTROl ROD REACTIVITY CONTROL LOSS OF NON-EMERGENCY AC POWER TO THE STATION AUXILIARIES POWER PRESSURIZER SAFETY VALVES SG SAFETY VALVES SAFETY VALVES OPEN TO RELIEVE SECONDARY SYSTEM PRESSURE LOW-LOW SG LEVEL 2/'4 IN ONE SG LOSS OF OFFSITE POWER MANUAL 1/2 LOW-LOW SG LEVEL 2/._ IN 2/._ SG (TURBINE DRIVEN PUMPS) , ... :s ... , , AFWS , ... I \ ' s f t ' DELIVER AUXILIARY FW TO CONTROL COR£ HEAT REMOVAl I.* :'*: . .. -... **-:* .. * . .-::-'"' *"* r-0 (I) Ci). 0 * .. "'1 *.Z 0 :::g :3' ;)loo. ,-,., ,., ,., 0 > ,., :::g Ill Alfr .(GOP*.
- Iii .fD ****< .. 0 .,_. , ... :s r; '-... REACTOR fltiP . BIIEAK£iS , .. S F ... , COli TliOl AOOS . GRAVITY . IIISERTIOII . . .. . .... -PRES SUR I*ZEi SAfElY . VALVES ****; :* .. ';-". . FULL POWER * *.-,*.
SG l£V£l . 2N 1.1 Oil£ SG : i .** LOSS Of Of'FS ITE PowER MAIIUAL 1/2 S6 LEVEL 2/11 I II 2/11 SG DRIY.£11 l'ti4PS) *.:,_.:. *:--, 1 S F, , .. DELIVER AUXILIARY
- Fll rcr COMTROL CORE *. ti£AT
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3 > 0 ""T.::O cc: S:"'V >_, _, c: ::0 ::0 r-o .... ..., z 3 > .... z HIGH PRESSURIZER PRESSURE " OVERTBf'ERATURE LOW-1..011 SG lEvEl Ill AllY SG 51 SIGIIAL 0 CJ "' 0 >' 1:111 0 fn ""T1 .... (i) Lilt" c: .. ::0 >-n ..... *= (t1 >'t!a
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- 0-19 STARTUP OF AN INACTIVE REACTOR COOLANT LOOP tD"Tl o_ ::UG) oc z;:u om -.... lUI C* ""il? -N Oo z !ifC:.H VCT WATER LEVEL ALARM Al.llllll R.i,ll JRC>>> aF 1 DII£CIORS c: '1J m c en .,o )>0 z::u )>m r-m -<" en c;; :::0 m '1J 0 HIGH VCT WATER LEVEL ALARM AUOIIll COUIII IU£ fiOH 11 1 OliiCIOAS HIGH N[UIROII HUt SOUIC£ IlliG( ALJIM eves SUBCRIJIC&l JOO I.SIU lOll' liMit &UIMS 100 POSIIION" SIEP COUIIllR eves IIGN II(UIROK Hill :HIGH} POw£1 llNGl OVUIIMPUUUIIl OVUI'OW!I HIGN PIISSUAIIU PRISSUII HIGH PIIESSURillR WUU llVlL 100 INSUIIOM LIM I I lURKS' ROO POSIIIOII SliP COUMIU" ll AlUM ,-'( I 5 I I '* COIIIROL IOOS C.UVIIT INSUIION MIIIU&l COIIIIOl IMOI£ ,, 101(: 'LOW &110 LOW-lOW IIIII I "101 & SAHTY SYS liM NOll A: CtOS( MAI(UP wAUl CONIROL *&IriS. tlOSI CMAIGING liNI COIIIROI.
VllWU, lltNIIIll£ CHli&IIG P\flP flOW IIIUil If M!CIS5lRT 56 SAHfY WAlWlS
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- RUPTURE OF A COIHROL ROO ) DRIVE MECHANISM HOUSING ZERO POWER l FULL POWER I v T HIGH NEUTRON FLUX (HIGH) 2N 1-POWER RANGE PRESSURIZER PRESSURIZER RTS HIGH NEUTRON FLUX (LOW) 2/ij SAFETY SAFETY VALVES VALVES POWER RANGE , r'* PASSIVE PASSIVE IS HIGH NEUTRON FLUX RATE \ ' I I I POWER RANGE REACTOR TRIP SAFETY VALVES ) I< SAFETY VALVES BREAKERS OPEN TO RELIEVE OPEN TO RELIEVE RCS PRESSURE RCS PRESSURE , r IS '* I , CONTROL RODS GRAY lTV INSERTION PASSIVE CONTROL ROD REACTIVITY CONTROL , LOW PRESSURIZER 2/ij I PRESSURE HIGH-3 CONTAINMENT 2/ij HIGH-I CONTAINMENT 2/3 PRESSURE 1 PRESSURE 1/2 HIGH-3 2/ij MANUAL 1 PRESSURE l I £SFAS I l ESFAS I ms l (<!)SIGNAL) (SI SIGNAL) SIGNAL) , ' \ , \ IS :s : s \ F' F ' F ' '* , I ' ' , NOTE I NOTE I -*
LOW PRESSURIZER PRESSURE MANUAL 1/2 WOLF CREEK INADVERTENT ECCS OPERATION AT POWER RTS ......... , ' I S F I \ I ... '" .... REACTOR TRIP BREAKERS .... '"'\ Is F' I I ' ..... " CONTROL RODS GRAVITY INSERTION PASSIVE .. .. CONTROL ROD CONTROL WOLFCREEK Rev.13 UPDATED SAFETY ANALYSIS REPORT FIGURE 15.0-22 INADVERTENT ECCS OPERATION
- ATPOWER
- l OVERTEMPERATURE 2/IJ
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- c: -a c )> n1 c C/1 :J>:e ;Do )>0 z;o )>m (/) c;; ::u m ., 0 L 0o Plt55UIIlU PtlSSUIIf Sl SIGNAL 01/ERTEMPERATURE
'&00 IJ I ORAl I DU !If I CAll ON tY SAHPLI NG SCi SHELL SIDE llUIO REQUIRED If NOI IDENIIFIIO IT SG LlWEL INDICAIION. .. OPUAIOR INIIIUlS OPEUIIOII Of llSIDUAL IIUI llHOVAl SfSilM AI APPROPIIAIE RCS (OJoOIIIONS. LOW PllfSSURilU PRESSURE OPERAIOR (SI)
- OP£Rlf0R (CI-PIIASE A) IOOINOIES:
I. SEQUENCE Of fVENIS 510111 IS fCII A COIIOI 11011 01 NO OF IStrE POWER B£1NG AVAILABLE COINCIDENCE wiiH SCi lUBE RUPIURE. 2. SEE SECIIOII 7.5 (I) fOR INDICA IOU AND RECORDUS AVAILABLE 10 IKE OPERA lOR FOLLOWING EYER I. ), OPUUOR ACIIONS INCLUDES OPUAIIOII Of rALVU UO flOW CONIROL RE!/IIIkED 10 DIJIP SlUM ANO lc£0UCE RCS PkESSUic(.
- 5 CJ) CJ) 0 , 0 0 0 !; z .... )> 0 0 6 m z -t lOW PRlSSUIIZER PIIUSUIIE Sl SIGitll 2/14 * -RE9IJI R£0 FOR IREAICS SMALlER THAll I nt OP£11ATOR IS I' HIGtl*l COIIUIIHNT 2/3 RTS OPUAIOI :aT) (liT SIGH.ll)
PR£SSUII£ LOW PRESSUIIZER 2/'4 ESFAS (SI SIGNAL) OJHU c: -u c )> c en , (5 rile c: ..... :J>n Cll z:u 0 )>m
- r-m N U'l -<" en -en :u m "'0 ::u 0 a. < . w 's ;, '... ' IIUCTOI TtiP 811UilRS COIITIOI.
RODS GRAVITI' INSERT 10M PASSIVE ' , COitTROl ROO REACTIVITY COIIfROl PRESSURE NAill fW I SOU HOlt ' AfWS ts r': ... , COitfROl SECOitOARY' lfEA T RO<<>YAL ESWS tSIF' 0 ECCS Cl REC IRCULA TIOII 'sf\ :s r', \. ./ AFTER .. , 10HOURS ccws " ' tS P '* ,' SUPPORT SYSTEMS OPERA l IOitAl ' ECCS Hl R£CIRCUUTIOII " \ f $ f I '.. , CORE COOl I MG
- OPERATOR ACTION INCLUDES VALVE ALIGNMENT ANO PUMP CONTROL REGU.RED FOR RECIRCULATION
- OPERATOR AUGNS SPRAY PUMP SUCTION FOR RECIRCULATION TO CONTAINMENT SUMP ON LO*LO RYJST LEVEL ALARM FOOTNOTE:
SEE SECTION 7.5(N) FOR INDICATORSANO RECORDERS AVAILABLE TO THE OPERA TOR FOLLOWNG EVENT OPUUOII (CI-PHAS£ A) Of'ERA TOR ( CS t HIGit-3 COIHAIMIIT PRESSURE l COHTAINKMT ISOUTIOII COfllliMKIIT lEAKAGE CONTROL ESfAS ((!) SIGilll) 2/'1 COIITliiiKMT cs l D10Sf'H£RE STSlEM RECIICUUTIOII ( IIIJECTION) SYSTEM 1 COMT. PR£S. KUT REMOVAL AMO ACTIVHY' COMTIOl
- OPUAJOR (CS) H NIGH-3 COMT.UII£11 2/'t PRUSlJIE _j AUXILIARY BLDG DUCT RADIATION MONITOR CREEK CVCS LETDOWN LINE RUPTURE REACTOR COOLANT ACTIVITY RELEASE TO AUXILIARY BLDG ATMOSPHERE UNFILTERED RELEASE TO ATMOSPHERE OPERATOR CLOSES LETDOWN ISOLATION VALVE AFTER RECEIPT OF THE ALARM WITHIN 30 MINUTES .. WO r CREEK UPDATED SAPBTY ARALYSIS REPORT Rev. 0 FIGURE 15.0-26 eves LETDOWN LINE RUPTURE
- *
- VENTILATION VENT WOLF CREEK GWPS GAS DECAY TANK RUPTURE RELEASE TO SUI LDING ATMOSPHERE UNFILTERED RELEASE TO ATMOSPHERE RADIATION MONITOR WASTE GAS RELEASED DIRECTLY TO ENVIRONMENT DURING TWO HOUR PERIOD WOLFCREEK Rev.13 UPDATED SAFETY ANALYSIS REPORT FIGURE 15.0-27 GWPS GAS DECAY TANK RUPTURE I I LIQUID RELEASE TO GROUND I ENTERS GROUNDWATER
- See Section 2.4.13 I ... --**-*** ... * **---------..
' \'X>LF CREEK RECYCLE HOLDUP TANK .. FAILURE (56,000 GAL) '(. GASES. RELEASE TO , BUILDING ATMOSPHERE* . UNFILTERED RELEASE. TO . ATMOSPHERE WOLP CREEK UPDATED SAPETY ANALYSIS REPORT Rev. 1 FIGURE 15.0-28 FLOOR DRAIN TANK FAILURE WOLF CREEK FUEL HANDLING ACC1DENT IN FUEL BUILDING GAS.ES RELEASED FROM FUEL POOL WATER I' .. I SF \ ' " FILTERED BY ESF *EMERGENCY VENTILATION SYSTEM IODINE ADSORBER TO ATMOSPHERE RADIOLOGICAL CONTROL WOL!' CRBBlt SAPBT! ARALYSIS Rev. 0 FIGURE 15.0-29 FUEL HANDLING' ACCIDENT IN FUEL BUILDING Rev. 0 W)LF CREEK FUEL HANDLING ACCIDENT INSIDE CONTAINMENT ACTIVITY RELEASED FROM REFUELING POOL (0-2HRS) CONTAINMENT RADIATION MONITORS DETECT HIGH ACTIVITY AND ISOLATE CONTAINMENT RADIOACTIVITY CONTAINED WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.0-30 FUEL HANDLING ACCIDENT INSIDE CONTAINMENT
CREEK SPENT FUEL CASK DROP (FROM EQUIVALENT 30FT) Rev. 0 NO RELEASE; NO CASK DAMAGE WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.0-31 SPENT FUEL CASK DROP ACCIDENT WOLF CREEK 15.1 INCREASE IN HEAT REMOVAL BY THE SECONDARY SYSTEM A number of events have been postulated which could result in an increase in heat removal from the reactor coolant system (RCS) by the secondary system.
Detailed analyses are presented for the following events, which have been
identified as the most limiting cases:
- a. Feedwater system malfunctions that result in a decrease in feedwater temperature
- b. Feedwater system malfunctions that result in an increase in feedwater flow
- c. Excessive increase in secondary steam flow
- d. Inadvertent opening of a steam generator atmospheric relief or safety valve
- e. Steam system piping failure
The above are considered to be ANS Condition II events, with the exception of steam system piping failures, which are considered to be ANS Condition III (minor) and Condition IV (major) events. Section 15.0.1 provides a discussion of ANS classifications and applicable acceptance criteria. All of the accidents in this section have been analyzed. It has been determined that the most severe radiological consequences will result from the
main steam line break accident discussed in Section 15.1.5. Therefore, the
radiological consequences are only reported for that limiting case. 15.1.1 FEEDWATER SYSTEM MALFUNCTIONS THAT RESULT IN A DECREASE IN FEEDWATER TEMPERATURE 15.1.1.1 Identification of Causes and Accident Description Reductions in feedwater temperature will cause an increase in core power by decreasing the reactor coolant temperature. Such transients are attenuated by
the thermal capacity of the secondary plant and the RCS. The
overpower/overtemperature protection (neutron overpower, overtemperature, and
overpower DT trips) prevents any power increase which could lead to a departure
from nucleate boiling ratio (DNBR) less than the safety analysis limit. 15.1-1 Rev. 13 WOLF CREEK A reduction in feedwater temperature may be caused by a spurious heater drain pump trip. In the event of a spurious heater drain pump trip, there is a
sudden reduction in feedwater inlet temperature to the steam generators. At
power, this increased subcooling will create a greater load demand on the RCS. With the plant at no-load conditions, the addition of cold feedwater may cause a decrease in RCS temperature, and thus a reactivity insertion due to the effects of the negative moderator coefficient of reactivity. However, the rate
of energy change is reduced as load and feedwater flow decrease, so the no-load transient is less severe than the full power case. The net effect on the RCS due to a reduction in feedwater temperature is similar to the effect of increasing secondary steam flow, i.e., the reactor will reach a new equilibrium condition at a power level corresponding to the new steam generator T. A decrease in normal feedwater temperature is classified as an ANS Condition II event, fault of moderate frequency. See Section 15.0.1 for a discussion of
Condition II events. The protection available to mitigate the consequences of a decrease in feedwater temperature is the same as that for an excessive steam flow increase, as discussed in Section 15.0.8 and listed in Table 15.0-6. 15.1.1.2 Analysis of Effects and Consequences Method of Analysis This transient is analyzed by computing conditions at the feedwater pump inlet following a heater drain pump trip. These feedwater conditions are then used to
recalculate a heat balance through the high pressure heaters. This heat
balance gives the new feedwater conditions at the steam generator inlet. The following assumptions are made:
- a. Plant initial power level corresponding to guaranteed nuclear steam supply system thermal output
- b. Heater drain pumps trip, resulting in a reduction in feedwater temperature Plant characteristics and initial conditions are further discussed in Section 15.0.3. 15.1-2 Rev. 0 WOLF CREEK Results A trip of the heater drain pumps causes a reduction in feedwater temperature that increases the thermal load on the primary system. The calculated reduction in feedwater temperature is 63.0 °F, resulting in an increase in heat load on the primary system of less than 10 percent of full power. The
increased thermal load due to a spurious heater drain pump trip would result in a transient very similar (but of reduced magnitude) to that presented in
Section 15.1.3 for an excessive increase in secondary steam flow, which evaluates the consequences of a 10-percent step load increase. Therefore, the transient results of this analysis are not presented. The plant is expected to reach stabilized conditions at a power level slightly higher than the initial power level. Normal plant operating procedures would then be followed to reduce power. 15.1.1.3 Conclusions The decrease in the feedwater temperature transient is less severe than the increase in the feedwater flow event (see Section 15.1.2) and the increase in
the secondary steam flow event (see Section 15.1.3). Based on results
presented in Sections 15.1.2 and 15.1.3, the applicable acceptance criteria for
the decrease in feedwater temperature event have been met. 15.1.2 FEEDWATER SYSTEM MALFUNCTIONS THAT RESULT IN AN INCREASE IN FEEDWATER FLOW 15.1.2.1 Identification of Causes and Accident Description Addition of excessive feedwater will cause an increase in core power by decreasing the reactor coolant temperature. Such transients are attenuated by
the thermal capacity of the secondary plant and of the RCS. The
overpower/overtemperature protection (neutron overpower, overtemperature, and overpower DT trips) prevents any power increase which could lead to a DNBR less than the safety analysis limit. An example of excessive feedwater flow would be a full opening of a feedwater control valve due to a feedwater control system malfunction or an operator error. At power, this excess flow causes a greater load demand on the RCS due to increased subcooling in the steam generator. With the plant at no-load
conditions, the addition of cold feedwater may cause a decrease in the RCS temperature and thus a reactivity insertion in the presence of a negative moderator temperature coefficient of reactivity. 15.1-3 Rev. 7 WOLF CREEK Continuous addition of excessive feedwater is prevented by the steam generator high-high level trip, which initiates feedwater isolation. The feedwater isolation signal closes the feedwater isolation valves, the feedwater control valves, and trips the turbine and main feedwater pumps. However, trip of the main feedwater pumps is not part of the primary success path for accident mitigation, and no direct credit is taken for the turbine trip function.
An increase in the normal feedwater flow is classified as an ANS Condition II
event, fault of moderate frequency. See Section 15.0.1 for a discussion of ANS
Condition II events.
Major plant systems and equipment available for mitigation of transient and
accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6.
The actual parameters assumed and results are given in the respective
section/subsection. Table 15.0-6 incorporates events shown in the sequence
diagram, Figure 15.0-8.
15.1.2.2 Analysis of Effects and Consequences
Method of Analysis
The excessive heat removal due to a feedwater system malfunction transient is
analyzed by using the detailed digital computer code RETRAN (Ref. 5). This
code simulates a multiloop system, neutron kinetics, the pressurizer, pressurizer relief and safety valves, pressurizer spray, steam generator, and
steam generator safety valves. The code computes pertinent plant variables, including temperatures, pressures, and power level. VIPRE-01 (Ref. 6) is used
to determine the core thermal limits to determine DNBR. RETRAN generated
statepoints are used as VIPRE-01 boundary conditions to perform the DNB
analysis.
The system is analyzed to demonstrate plant behavior in the event that
excessive feedwater addition occurs due to a control system malfunction or
operator error that allows a feedwater control valve to open fully. Two cases
are analyzed, assuming a conservatively large negative moderator temperature
coefficient:
- a. Accidental opening of two feedwater control valves with
the reactor just critical at zero load conditions
- b. Accidental opening of two feedwater control valves with
the reactor in automatic control at full power
The reactivity insertion rate following a feedwater system malfunction is
calculated with the following assumptions:
- a. For the feedwater control valve accident at full power, two feedwater control valves are assumed to malfunction, resulting in a step increase to 200 percent of nominal
feedwater flow to two steam generators.
15.1-4 Rev. 27 WOLF CREEK
- b. For the feedwater control valve accident at zero load conditions, a feedwater control valve malfunction occurs, which results in an
increase in flow to two steam generators from zero to 250 percent
of the nominal full load value for two steam generators.
- c. For the zero load condition, feedwater temperature is at a conservatively low value of 32 °F.
- d. No credit is taken for the heat capacity of the RCS and steam generator thick metal structure in attenuating the
resulting plant cooldown.
- e. The feedwater flow resulting from two fully open control valves is terminated by a steam generator high-high level trip signal, which initiates feedwater isolation. The feedwater isolation signal closes the feedwater isolation vales, the feedwater control valves, and trips the main feedwater pumps. However, trip of the main feedwater pumps is not part of the primary success path for accident mitigation.
Plant characteristics and initial conditions are further discussed in Section
15.0.3.
Subsequent to feedwater isolation initiated by a steam generator high-high
level trip, the reactor continues to operate until the low-low steam generator
level setpoint is reached. No credit is taken in the licensing basis analysis
for a reactor trip on turbine trip. No single active failure will prevent
operation of the reactor protection system. A discussion of anticipated
transients without scram (ATWS) considerations is presented in Section 15.8.
Results In the case of an accidental full opening of two feedwater control valves with
the reactor at zero power and the above mentioned assumptions, the maximum
reactivity insertion rate is less than the maximum reactivity insertion rate
analyzed in Section 15.4.1 for an uncontrolled rod cluster control assembly (RCCA) bank withdrawal from a subcritical or low power startup condition. It
should be noted that if the incident occurs with the unit just critical at no-
load, the reactor may be tripped by the power range high neutron flux trip (low
setting) set at approximately 25 percent of nominal full power.
The full power case (maximum reactivity feedback coefficients, with rod
control) results in the greatest power increase. Assuming no rod control, the
case results in a similar transient.
15.1-5 Rev. 27 WOLF CREEK The feedwater flow resulting from two fully open control valves is terminated
by a steam generator high-high level trip signal, which initiates feedwater
isolation. The feedwater isolation signal closes the feedwater isolation valves, the feedwater control valves, and trips the main feedwater pumps. However, trip of the main feedwater pumps is not part of the primary success path for accident mitigation. This prevents continuous addition of the feedwater. Once main feedwater is isolated, the reactor continues to operate
until the lo-lo steam generator trip setpoint is reached.
When the lo-lo steam generator level setpoint is reached the reactor is tripped
and the control rods fall into the core terminating the event.
Transient results presented in Figures 15.1-1 and 15.1-2, and 15.1-2A for the full power case show the increase in nuclear power and T associated with the increased thermal load on the reactor. The DNBR does not drop below the safety analysis limit. Following the reactor trip, the plant approaches a stabilized
condition. Standard plant shutdown procedures may then be followed to further
cool down the plant.
Since the power level rises during the excessive feedwater flow incident, the
fuel temperatures will also rise until after reactor trip occurs. The core
heat flux lags behind the neutron flux response due to the fuel rod thermal
time constant, hence the peak value of heat flux does not exceed 118 percent of
its nominal value (i.e., the assumed high neutron flux trip setpoint). The
peak fuel temperature will thus remain well below the fuel melting temperature.
The transient results show that DNB does not occur at any time during the
excessive feedwater flow incident. Thus, the ability of the reactor coolant to
remove heat from the fuel rod is not reduced. The fuel cladding temperature, therefore, does not rise significantly above its initial value during the
transient.
The calculated sequence of events for this accident is presented in Table 15.1-
- 1.
15.1.2.3 Conclusions
The results of the analysis show that the DNBRs encountered for an excessive
feedwater addition at power are above the limiting value. The DNBR design
basis is described in Section 4.4. Additionally, it has been determined that
the reactivity insertion rate which occurs at no-load conditions following
excessive feedwater addition is less than the maximum value considered in the
analysis of the rod withdrawal from subcritical condition analysis, presented
in Section 15.4.1.
15.1-6 Rev. 27 WOLF CREEK 15.1.3 EXCESSIVE INCREASE IN SECONDARY STEAM FLOW 15.1.3.1 Identification of Causes and Accident Description An excessive increase in secondary system steam flow (excessive load increase incident) is defined as a rapid increase in steam flow that causes a power
mismatch between the reactor core power and the steam generator load demand.
The reactor control system is designed to accommodate a 10-percent step load
increase or a 5-percent per minute ramp load increase in the range of 15 to 100
percent of full power. Any loading rate in excess of these values may cause a reactor trip actuated by the reactor protection system. Steam flow increases greater than 10 percent are analyzed in Sections 15.1.4 and 15.1.5. This accident could result from either an administrative violation, such as excessive loading by the operator, or an equipment malfunction in the turbine
bypass control or turbine speed control. During power operation, turbine bypass to the condenser is controlled by reactor coolant condition signals, i.e., high reactor coolant temperature indicates a need for turbine bypass. A single controller malfunction does not cause turbine bypass; an interlock is provided which blocks the opening of the
valves unless a large turbine load decrease or a turbine trip has occurred. Protection against an excessive load increase accident is provided by the following reactor protection system signals:
- a. Overpower T b. Overtemperature T c. Power range high neutron flux An excessive load increase incident is considered to be an ANS Condition II event, fault of moderate frequency. See Section 15.0.1 for a discussion of
Condition II events. Major plant systems and equipment available for mitigation of transient and accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6. The actual parameters assumed and results are given in the respective section/subsection. Table 15.0-6 incorporates events shown in the sequence diagram, Figure 15.0-9. 15.1.3.2 Analysis of Effects and Consequences Method of Analysis This accident is analyzed using the LOFTRAN code (Ref. 1). The code simulates the neutron kinetics, RCS, pressurizer, pressurizer relief and safety valves, pressurizer spray, steam generator, steam generator safety valves, and
feedwater system. The code computes pertinent plant variables, including
temperatures, pressures, and power level. VIPRE-01 (Ref. 6) is used to
determine the core thermal limits to determine DNBR. LOFTRAN generated
statepoints are used as VIPRE-01 boundary conditions to perform the DNB
analysis. 15.1-7 Rev. 13 WOLF CREEK Four cases are analyzed to demonstrate the plant behavior following a 10-percent step load increase from rated load. These cases are as follows:
- a. Reactor control in manual with minimum moderator reactivity feedback
- b. Reactor control in manual with maximum moderator reactivity feedback
- c. Reactor control in automatic with minimum moderator reactivity feedback
- d. Reactor control in automatic with maximum moderator reactivity feedback For the minimum feedback cases, the core has the most positive moderator temperature coefficient of reactivity, therefore, reductions in coolant temperature will have the least impact on core power. For the maximum feedback
cases, the moderator temperature coefficient is assumed at the most negative value. This results in the largest amount of reactivity feedback due to changes in coolant temperature. For the cases with automatic rod control, no credit was taken for T trips on overtemperature or overpower in order to demonstrate the inherent transient capability of the plant. Under actual operating conditions, such a trip may occur, after which the plant would
quickly stabilize. A 10-percent step increase in steam demand is assumed, and all cases are studied without credit being taken for pressurizer heaters. Initial operating
conditions are assumed at nominal values, consistent with steady-state full power operation, following statistical core design (SCD) methodology. Plant characteristics and initial conditions are further discussed in Section 15.0.3. Normal reactor control systems and engineered safety systems are not required to function. The reactor protection system is assumed to be operable; however, reactor trip is not encountered for most cases due to the error allowances assumed in the setpoints. No single active failure will prevent the reactor protection system from performing its intended function. 15.1-8 Rev. 7 WOLF CREEK Results Figures 15.1-3 through 15.1-6 illustrate the transient with the reactor in the manual control mode. As expected, for the minimum moderator feedback case there is a slight power increase, and the average core temperature shows a large decrease. This results in a DNBR which increases above its initial value. For the maximum moderator feedback manually controlled case there is a much larger increase in reactor power, due to the moderator feedback. A reduction in DNBR is experienced, but DNBR remains above the safety analysis
limit.Figures 15.1-7 through 15.1-10 illustrate the transient, assuming that the reactor is in the automatic control mode and no reactor trip signals occur.
Both the minimum and maximum moderator feedback cases show that core power
increases, thereby reducing the rate of decrease in coolant average temperature
and pressurizer pressure. For both of these cases, the minimum DNBR remains above the safety analysis limit. For all cases, the plant rapidly reaches a stabilized condition at the higher power level. Normal plant operating procedures would then be followed to
reduce power. Note that due to the measurement errors assumed in the setpoints, it is possible that reactor trip could actually occur for the automatic control cases. The plant would then reach a stabilized condition
following the trip. The excessive load increase incident is an overpower transient for which the fuel temperatures will rise. Reactor trip may not occur for some of the cases
analyzed, and the plant reaches a new equilibrium condition at a higher power
level corresponding to the increase in steam flow. Since DNB does not occur at any time during the excessive load increase transients, the ability of the reactor coolant to remove heat from the fuel rod
is not reduced. Thus, the fuel cladding temperature does not rise significantly above its initial value during the transient. The calculated sequence of events for the excessive load increase incident is shown in Table 15.1-1. 15.1.3.3 Conclusions The analysis presented above shows that for a 10-percent step load increase, the DNBR remains above the safety analysis limit; the design basis for DNBR is described in Section 4.4. The plant rapidly reaches a stabilized condition, following the load increase. 15.1-9 Rev. 13 WOLF CREEK 15.1.4 INADVERTENT OPENING OF A STEAM GENERATOR ATMOSPHERIC RELIEF OR SAFETY VALVE 15.1.4.1 Identification of Causes and Accident Description The most severe core conditions resulting from an accidental depressurization of the main steam system are associated with an inadvertent opening of a single
turbine bypass, atmospheric relief, or safety valve. The analyses performed, assuming a rupture of a main steam line, are given in Section 15.1.5. The steam release, as a consequence of this accident, results in an initial increase in steam flow followed by a decrease in steam flow during the rest of
the accident as the steam generator pressure decreases. The energy removal
from the RCS causes a reduction of coolant temperature and pressure. In the
presence of a negative moderator temperature coefficient, the cooldown results
in an insertion of positive reactivity. The analysis is performed to demonstrate that the following criterion is satisfied: Assuming a stuck RCCA, with offsite power available, and assuming a single failure in the engineered safety features system, there will be no consequential damage to the core or reactor coolant system after reactor trip
for a steam release equivalent to the spurious opening, with failure to close, of the largest of any single steam dump, atmospheric relief, or safety valve. Accidental depressurization of the secondary system is classified as an ANS Condition II event. See Section 15.0.1 for a discussion of Condition II
events.The following systems provide the necessary protection against an accidental depressurization of the main steam system:
- a. Safety injection system actuation from any of the following:
- 1. Two out of four low pressurizer pressure signals
- 2. Two out of three low steam line pressure signals in any one loop
- b. The overpower reactor trips (neutron flux and T) and the reactor trip occurring in conjunction with receipt of the SIS 15.1-10 Rev. 13 WOLF CREEK
- c. Redundant isolation of the main feedwater lines
Sustained high feedwater flow would cause additional
cooldown. Therefore, in addition to the normal control
action which will close the main feedwater valves
following reactor trip, an SIS will rapidly close all
feedwater control valves and back up feedwater isolation
valves. The SIS will also trip the main feedwater pumps, and close the feedwater pump discharge valves; however, trip of the main feedwater pumps is not part of the primary success path for accident mitigation.
- d. Trip of the fast-acting main steam line isolation valves
(designed to close in less than 5 seconds) on:
- 1. Safety injection system actuation derived from two
out of three low steam line pressure signals in any
one loop (above Permissive P-11)
- 2. Two out of three high negative steam pressure rates
in any loop (below Permissive P-11)
Major plant systems and equipment available for mitigation of transient and
accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6.
The actual parameters assumed and results are given in the respective
section/subsection. Table 15.0-6 incorporates events shown in the sequence
diagram, Figure 15.0-10.
15.1.4.2 Analysis of Effects and Consequences
Method of Analysis
The following analyses of a secondary system steam release are performed for
this section:
- a. A full plant digital computer simulation, using the
RETRAN code (Ref. 5) to determine RCS temperature and
pressure during cooldown, and the effect of safety
injection. VIPER-01 (Ref. 6) is used to determine the core thermal limits to determine DNBR. RETRAN generated statepoints are used as VIPRE-01 boundary conditions to perform the DNB analysis.
- b. Analyses to determine that there will be no
consequential damage to the core or reactor coolant
system.
The following conditions are assumed to exist at the time of a secondary steam
system release:
- a. End-of-life shutdown margin at no-load, equilibrium
xenon conditions, and with the most reactive RCCA stuck
in its fully withdrawn position. Operation of RCCA
banks during core burnup is restricted by the insertion
limits so that addition of positive reactivity in a
secondary system steam release accident will not lead to
a more adverse condition than the case analyzed.
15.1-11 Rev. 27 WOLF CREEK b. A negative moderator coefficient corresponding to the end-of-life rodded core with the most reactive RCCA in the fully withdrawn position. The variation of the coefficient with temperature and pressure is included. The K eff versus temperature at 1,000 psia corresponding to the negative moderator temperature coefficient used is shown in Figure 15.1-11. c. Minimum capability for injection of RWST boron solution corresponding to the most restrictive single failure in the safety injection system. This corresponds to the flow delivered by one centrifugal charging pump delivering flow to the cold leg header and taking suction from the RWST. Reactor coolant seal injection flow is not included in the total core delivery. The volume downstream of the RWST must be swept prior to delivery of boric acid to the reactor coolant loops. d. The case studied is a steam flow of 268 pounds per second at 1,200 psia, with offsite power available. This is the maximum capacity of any single turbine bypass, atmospheric relief, or safety valve. Initial hot standby conditions (557 F average coolant temperature) at time zero are assumed, since this represents the most conservative initial condition. Should the reactor be just critical or operating at power at the time of a steam release, the reactor will be tripped by the normal overpower protection when power level reaches a trip point. Following a trip at power, the RCS contains more stored energy than at no-load, the average coolant temperature is higher than at no-load, and there is appreciable energy stored in the fuel. Thus, the additional stored energy is removed via the cooldown caused by the steam release before the no-load conditions of RCS temperature and shutdown margin assumed in the analyses are reached. After the additional stored energy has been removed, the cooldown and reactivity insertions proceed in the same manner as in the analysis which assumes no-load condition at time zero. However, since the initial steam generator water inventory is greatest at no-load, the magnitude and duration of the RCS cooldown are less for steamline release occurring at power. e. In computing the steam flow, the Moody Curve (Ref. 2) for fL/D = 0 is used.
- f. Perfect moisture separation in the steam generator is assumed.
- g. Offsite power is assumed, since this would maximize the cooldown.
- h. Maximum cold auxiliary feedwater flow is assumed.
- i. Four reactor coolant pumps are operating. 15.1-12 Rev. 22 WOLF CREEK Results The results presented are a conservative indication of the events which would occur, assuming a secondary system steam release, since it is postulated that
all of the conditions described above occur simultaneously. Figures 15.1-12 and 15.1-13 show the transient results for a steam flow of 268 lb/sec at 1,200 psia. The assumed steam release is greater than or equal to the capacity of any single steam dump, atmospheric relief, or safety valve. Safety injection is initiated automatically by low pressurizer pressure. Operation of one
centrifugal charging pump is assumed. Boron solution from the RWST enters the
RCS, providing sufficient negative reactivity to prevent core damage. The
transient is quite conservative with respect to cooldown, since no credit is
taken for the energy stored in the system metal other than that of the fuel
elements and steam generator tubes. Since the transient occurs over a period of about 600 seconds, the neglected stored energy is likely to have a significant effect in slowing the cooldown.
The calculated time sequence of events for this accident is listed in Table
15.1-1.15.1.4.3 Conclusions The analysis shows that the criteria stated earlier in this section are satisfied. For an accidental depressurization of the main steam system, the DNB design limits are not exceeded. This case is less limiting than the steamline rupture case described in Section 15.1.5. 15.1.5 STEAM SYSTEM PIPING FAILURE
15.1.5.1 Identification of Causes and Accident Description The steam release arising from a rupture of a main steam line would result in an initial increase in steam flow that decreases during the accident as the
steam generator pressure decreases. The energy removal from the RCS causes a reduction of coolant temperature and pressure. In the presence of a negative moderator temperature coefficient, the cooldown results in an insertion of positive reactivity. If the most reactive RCCA is assumed stuck in its fully withdrawn position after reactor trip, there is possibility that the core will become critical and return to power. A return to power following a steam line rupture is a potential problem mainly because of the high power peaking factors which exist, assuming the most reactive RCCA to be stuck in its fully withdrawn position. The core is ultimately shut down by the boric acid solution delivered by the emergency core cooling system. 15.1-13 Rev. 22 WOLF CREEK The analysis of a main steam line rupture is performed to demonstrate that the following criteria are satisfied: Assuming a stuck RCCA with or without offsite power, and assuming a single failure in the engineered safety features system, the core cooling capability is maintained. Radiation doses do not exceed the guidelines of 10 CFR 100. Although DNB and possible clad perforation following a steam pipe rupture are not necessarily unacceptable, the following analysis, in fact, shows that the DNB design basis is not exceeded for any rupture, assuming the most reactive
control rod assembly stuck in its fully withdrawn position. The DNBR design
basis is discussed in Section 4.4. A major steam line rupture is classified as an ANS Condition IV event. See Section 15.0.1 for a discussion of Condition IV events. Effects of minor secondary system pipe breaks are bounded by the analysis presented in this section. Minor secondary system pipe breaks are classified
as Condition III events, as described in Section 15.0.1.3. The methodology for analyzing the reactor core response to excessive secondary steam releases is documented in WCAP-9226 (Reference 3). This WCAP, known as the Steamline Break Topical, examined the effect of power level (including full power cases), break size, and plant variations for typical three-loop and four-loop Westinghouse-designed PWRs. This WCAP concludes that the largest double-ended steamline rupture at end-of-life, hot zero-power (Mode 2) conditions, with the most reactive RCCA in the fully withdrawn position, bounds all other power levels and other Modes for the post-trip phase of the transient. Note that the conclusion that the hot-zero power case is the limiting case is based on certain specific protection system performance characteristics credited for at power steamline break analyses. Since the WCAP was first issued, plant modifications have been made which might not be bounded by the generic assumptions of the WCAP, such as increases in the Overpower T response times, lead/lag time constant changes, reduced Low Steam Pressure setpoints, etc. As a result, the full power steamline break event, which credits the OverpowerT reactor trip function, could be initiated from the plant conditions that are outside the limits of applicability. A Wolf Creek specific analysis for steamline breaks occurring while the reactor is at power has been performed to confirm the conclusions documented in WCAP-9226 are valid, even with assumed parameters being outside the generic limits established by Westinghouse. The analysis demonstrates the adequacy of the protection systems by showing that with the appropriate actions of these systems, the DNB design basis is satisfied and fuel centerline melting is precluded. As such, a detailed analysis of this transient with the largest double-ended rupture at the hot-zero power conditions, is presented here. During startup or shutdown evolutions, when the operator manually blocks the safety injection on low pressurizer pressure or low steamline pressure and
steamline isolation on low steamline pressure when pressurizer pressure is less than P-11 setpoint (i.e., 1970 psig), the steamline pressure-negative rate-high signal is automatically enabled to provide steamline isolation. For inside
containment breaks, steamline isolation may also be provided by the containment
pressure High-2 signal and safety injection would be actuated by the 15.1-14 Rev. 22 WOLF CREEK containment pressure High-1 signal. For a steamline break occurring outside containment, an automatic actuation signal for safety injection would not be
available. Since the steamline break could occur outside containment, it is
possible to have a steamline break event below the P-11 interlock setpoint that
does not generate a safety injection actuation of borated ECCS flow. With no
borated ECCS flow supplied to the core, a return to criticality and subsequent
power excursion in the core would result.
However, the combined effect of the negative reactivity associated with the
initial RCS boration requirement to meet the shutdown margin and the steamline
isolation provided by the steamline high pressure negative rate trip function
to limit the steam blowdown would be more than sufficient to limit the core
power excursion following a return to criticality. Analysis results confirm
that the consequences of a postulated steamline break event occurring in Mode 3
below P-11 with the safety injection being blocked, would be bounded by the
limiting steamline break scenario initiating from the HZP conditions with a 0
ppm boron concentration. Therefore, boration to cold shutdown conditions prior
to SI blocking is not necessary.
The following functions provide the protection for a steam line rupture:
- a. Safety injection system actuation from any of the
following:
- 1. Two out of four low pressurizer pressure signals
- 2. Two out of three high-1 containment pressure
signals
- 3. Two out of three low steam line pressure signals in
any one loop
- b. The overpower reactor trips (neutron flux and T) and the reactor trip occurring in conjunction with receipt of the SIS.
- c. Redundant isolation of the main feedwater lines
Sustained high feedwater flow would cause additional
cooldown. Therefore, in addition to the normal control
action, which will close the main feedwater valves
following a reactor trip, an SIS will rapidly close all
feedwater control valves and back up feedwater isolation
valves. The SIS will also trip the main feedwater pumps, and close the feedwater pump discharge valves; however, trip of the main feedwater pumps is not part of the primary success path for accident mitigation.
- d. Trip of the fast acting main steam line isolation valves (designed to close within the limits of Figure B 3.7.2-1,
shown in Technical Specification Bases) on:
- 1. High-2 containment pressure
- 2. Safety injection system actuation derived from two
out of three low steam line pressure signal in any
one loop (above Permissive-11)
- 3. Two out of three high negative steam pressure rate
in any one loop (below Permissive-11)
15.1-15 Rev. 27 WOLF CREEK Fast-acting isolation valves are provided in each steam line; these valves will fully close within the limits of Figure B 3.7.2-1, shown in Technical
Specification Bases, upon receipt of an isolation actuation signal, following a
large break in the steam line. For breaks downstream of the isolation valves, closure of all valves would completely terminate the blowdown. For any break
in any location, no more than one steam generator would experience an
uncontrolled blowdown, even if one of the isolation valves fails to close. A
description of steam line isolation is included in Chapter 10.0.
Flow restrictors are installed in the steam generator outlet nozzle, an
integral part of the steam generator. The effective throat area of the nozzles
is 1.4 square feet, which is considerably less than the main steam pipe area;
thus, the nozzles also serve to limit the maximum steam flow for a break at any
location.
Table 15.1-2 lists the equipment required in the recovery from a high energy
line rupture. Not all equipment is required for any one particular break, since the requirements will vary, depending upon postulated break size and
location. Design criteria and methods of protection of safety-related
equipment from the dynamic effects of postulated piping ruptures are provided
in Section 3.6.
Major plant systems and equipment available for mitigation of transient and
accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6.
The actual parameters assumed and results are given in the respective
section/subsection. Table 15.0-6 incorporates events shown in the sequence
diagram, Figure 15.0-10.
15.1.5.2 Analysis of Effects and Consequences
Method of Analysis
The analysis of the steam pipe rupture has been performed to determine:
- a. The core heat flux and RCS temperature and pressure resulting from the cooldown following the steam line break. RETRAN-3D computer code operating in the RETRAN-02 mode (Ref. 5) has been used.
- b. The thermal and hydraulic behavior of the core following a steam line break. A detailed thermal and hydraulic digital-
computer code, VIPRE (Ref. 6), has been used to determine if DNB
occurs for the core conditions computed in item a above.
The following conditions were assumed to exist at the time of a main steamline
break accident:
- a. End-of-life shutdown margin at no-load, equilibrium xenon conditions, and the most reactive RCCA stuck in its fully withdrawn position. Operation of the control rod banks during each operating cycle is restricted by the insertion limits so that addition of positive reactivity in a steam line break accident will not lead to a more adverse condition than the case analyzed.
- b. A negative moderator coefficient corresponding to the end-of-life rodded core with the most reactive RCCA in the fully withdrawn position. The variation of the coefficient with temperature and pressure has been included. The k eff versus temperature at 1,000 psia, corresponding to the negative moderator temperature coefficient used, is shown in Figure 15.1-11a.
15.1-16 Rev. 29 WOLF CREEK The effect of power generation in the core on overall reactivity is shown in Figure 15.1-14. The core properties associated with the sector nearest the affected steam generator and those associated with the remaining sector were conservatively combined to obtain average core properties for reactivity feedback calculations. Further, it was conservatively assumed that the core power distribution was uniform. These two conditions cause underprediction of the reactivity feedback in the high power region near the stuck rod. The stuck rod is assumed in the region of the core of lowest temperature. To verify the conservatism of this method, the reactivity, as well as the power distribution, was checked for the limiting conditions during the transient for the cases analyzed. This core analysis considered the Doppler reactivity from the high fuel temperature near the stuck RCCA, moderator feedback from the high water enthalpy near the stuck RCCA, power redistribution, and nonuniform core inlet temperature effects. For cases in which surface boiling occurs in the high heat flux regions of the core, the effect of void formation was also included. It was determined that the reactivity employed in the kinetics analysis was always larger than the reactivity calculated, including the above local effects for the limiting conditions during the transient. These results verify conservatism, i.e., underprediction of negative reactivity feedback from power generation. c. Minimum capability for injection of boron solution corresponding to the most restrictive single failure in the safety injection system. The emergency core cooling system consists of four subsystems: 1) the passive safety injection (SI) accumulators, 2) the residual heat removal system, 3) the SI system, and 4) the high head SI system (centrifugal charging pumps). Only the high head injection system (one CCP) is modeled for the steam line break accident analysis. The actual modeling of the safety injection system in RETRAN is as follows: The flow corresponds to full flow (less seal injection flow) of one charging pump delivering to the RCS via the cold leg header. No credit has been taken for the borated water that must be swept from the lines downstream of the RWST prior to the delivery of the boron solution from the RWST to the reactor coolant loops. The RWST Boron concentration is assumed to be 2300 ppm. 15.1-17 Rev. 22 WOLF CREEK For the cases where offsite power is assumed, the sequence of events in the safety injection system is as
follows. After the generation of the safety injection signal (appropriate delays for instrumentation, logic, and signal transport included), the appropriate valves
begin to operate, and the high head safety injection pump starts. In 12 seconds, the valves are assumed to be in their final position, and the pump is assumed to
be at full speed (see note in 15.1.5.5). The volume downstream of the RWST must be swept prior to delivery
of boric acid to the reactor coolant loops. This delay is included in the calculations. In cases where offsite power is not available, an additional 12-second delay is assumed to start the diesels and to load the necessary safety injection
equipment onto them.
- d. Since the steam generators are provided with integral flow restrictors with a 1.4-square-foot throat area, any
rupture with a break area greater than 1.4 square feet, regardless of location, would have the same effect on
the NSSS as the 1.4-square-foot break. The following
cases have been considered in determining the core power
and RCS transients:
- 1. Complete severance of a pipe, with the plant initially at no-load conditions, full reactor
coolant flow with offsite power available.
- 2. Case with loss of offsite power simultaneous with the steam line break, which causes initiation of the safety injection signal. Loss of offsite
power results in reactor coolant pump coastdown.
- e. Power peaking factors corresponding to one stuck RCCA and nonuniform core inlet coolant temperatures are
determined at end of core life. The coldest core inlet
temperatures are assumed to occur in the sector with the stuck rod. The power peaking factors account for the effect of the local void in the region of the stuck RCCA during the return to power phase following the steam line break. This void in conjunction with the large negative moderator coefficient partially offsets the effect of the stuck assembly. The power peaking factors depend upon the core power, temperature, pressure, and flow, and, thus, are different for each case studied. The core parameters used for each of the two cases correspond to values determined from the respective transient analysis. 15.1-18 Rev. 22 WOLF CREEK Both cases above assume initial hot standby conditions (557 F average coolant temperature) at time zero, including the application of conservative uncertainties to the initial RCS pressure, flow, and temperature, values, since this represents the most pessimistic initial condition. Should the reactor be just critical or operating at power at the time of a steam line break, the reactor will be tripped by the normal overpower protection system when power level reaches a trip point. Following a trip at power, the RCS contains more stored energy
than at no-load, the average coolant temperature is
higher than at no-load, and there is appreciable energy
stored in the fuel. Thus, the additional stored energy
is removed via the cooldown caused by the steam line
break before the no-load conditions of RCS temperature
and shutdown margin assumed in the analyses are
reached. After the additional stored energy has been
removed, the cooldown and reactivity insertions proceed
in the same manner as in the analysis, which assumes no-
load condition at time zero.
- f. In computing the steam flow during a steam line break, the Moody Curve (Ref. 2) for fL/D = 0 is used. g. AFW is activated immediately as the transient begins. Based upon the plant specific flow rate calculations, the AFW is assumed to be 1360.13 gpm to the faulted SG and 699.62 gpm to the intact SGs, for a total of 2059.75 gpm. h. Isolation of the mainsteam isolation valves (MSIVs) is assumed to occur beginning two seconds after a low compensated steamline pressure signal is received, with the MSIV closure occurring in a 15 second linear ramp. i. Isolation of the main feedwater isolation valves (MFIVs) is activated when SI signal is initiated, with a two second time delay. Closure of the MFIVs is delayed for 15 seconds following with an instantaneous closure.
Results The calculated sequence of events for both cases analyzed is shown on Table 15.1-1.The results presented are a conservative indication of the events which would occur, assuming a steam line rupture, since it is postulated that all of the
conditions described above occur simultaneously. Core Power and Reactor Coolant System Transient Figures 15.1-15 through 15.1-26 show the RCS transient and core heat flux following a main steam line rupture (complete severance of a pipe) at initial
no-load condition (case 1). Offsite power is assumed to be available so that full reactor coolant flow exists. The transient shown assumes an uncontrolled steam release from only
one steam generator. Should the core be critical at near zero power when the
rupture occurs, the initiation of safety injection by low steam line pressure
will trip the reactor. Steam release from more than one steam generator will be prevented by automatic trip of the fast-acting isolation valves in 15.1-19 Rev. 22 WOLF CREEK the steam lines by high containment pressure signals or by low steam line pressure signals. Even with the failure of one valve, release is limited to no
more than 20 seconds for the other steam generators while the one generator blows down. The main steam line isolation valves are designed to be fully
closed in less than 15 seconds from receipt of a closure signal. As shown in Figure 15.1-18, the core attains criticality with the RCCAs
inserted (with the design shutdown assuming one stuck RCCA) before the RWST boron solution enters the RCS. A peak core power significantly lower than the nominal full power value is attained. The calculation assumes that the boric acid is mixed with, and diluted by, the water flowing in the RCS prior to entering the reactor core. The concentration
after mixing depends upon the relative flow rates in the RCS and in the safety
injection system. The variation of mass flow rate in the RCS due to water
density changes is included in the calculation, as is the variation of flow
rate in the safety injection system due to changes in the RCS pressure. The
safety injection system flow calculation includes the line losses in the system as well as the pump head curve. Figures 15.1-21 through 15.1-26 show the salient parameters for case 2, which corresponds to the case discussed above with the additional loss of offsite power at the time the safety injection signal is generated. The safety
injection system delay time includes 12 seconds to start the diesel in addition to 12 seconds to start the safety injection pump and open the valves (see note in 15.1.5.5). Criticality is achieved later, and the core power increase is slower than in the similar case with offsite power available. The ability of
the emptying steam generator to extract heat from the RCS is reduced by the
decreased flow in the RCS. The peak power remains well below the nominal full
power value. It should be noted that following a steam line break only one steam generator blows down completely. Thus, the remaining steam generators are still
available for the dissipation of decay heat after the initial transient is
over. In the case of loss of offsite power, this heat is removed to the
atmosphere via the atmospheric relief or safety valves. Margin to Critical Heat Flux A DNB analysis was performed for both of these cases. It was found that both cases had a minimum DNBR greater than the safety analysis limit. The result of the DNBR calculation for the limiting SLB case (with offsite power available) is depicted in Figure 15.1-20a. The analysis demonstrated that the minimum DNBR remains above the limit value of 1.50 and, thus, it is concluded that the DNB design basis is met for the steam line break event initiated from zero power with the replacement MSIVs and MFIVs and associated actuators. 15.1-20 Rev. 22 WOLF CREEK 15.1.5.3 Radiological Consequences 15.1.5.3.1 Method Of Analysis 15.1.5.3.1.1 Physical Model
The radiological consequences of a MSLB inside the containment are less severe than the one outside the containment because the radioactivity released will be
held up inside the containment, allowing decay and plateout of the radionuclides. To evaluate the radiological consequences due to a postulated MSLB (outside the containment), it is assumed that there is a complete severance of a main steam line outside the containment. It is also assumed that there is a simultaneous loss of offsite power, resulting in reactor coolant pump coastdown. The safety injection system is actuated and the reactor trips. The main steam line isolation valves, their bypass valves, and the steam line drain valves isolate the steam generators and the main steam lines upon a
signal initiated by the engineered safety features actuation system under the
conditions of high steam negative pressure rate or low steam line pressure.
The main steam isolation valves are installed in the main steam lines from each
steam generator downstream from the safety and atmospheric relief valves outside the containment. The break in the main steam line is assumed to occur outside of the containment. The affected steam generator (steam generator
connected to a broken steam line) blows down completely. The steam is vented
directly to the atmosphere. Each of the steam generators incorporates integral flow restrictors, which are designed to limit the rate of steam blowdown from the steam generators
following a rupture of the main steam line. This, in turn, reduces the cooling rate of the reactor coolant system to preclude departure from nucleate boiling (DNB).In case of loss of offsite power, the remaining steam generators are available for dissipation of core decay heat by venting steam to the atmosphere via the atmospheric relief valves. Venting continues until the reactor coolant temperature and pressure have decreased sufficiently so that the RHR system can be utilized to cool the reactor. 15.1.5.3.1.2 Assumptions and Conditions The major assumptions and parameters assumed in the analysis are itemized in Tables 15.1-3 and 15A-1. 15.1-21 Rev. 13 WOLF CREEK The assumptions used to determine the concentrations of radioactive isotopes within the secondary system for this accident are as follows:
- a. The secondary system initial concentrations of radioactive isotopes are assumed to be the dose equivalent of 0.1 Ci/gm of 1-131.
- b. A primary-to-secondary leakage rate of 1 gpm is assumed to exist and is assumed to be in the affected steam generator.
- c. The reactor coolant concentration of radioactive isotopes is determined by two methods, and both cases are analyzed. These are:
- 1. The initial reactor coolant concentrations of radioactive isotopes are assumed to be the dose equivalent of 1.0 Ci/gm of I-131 with an iodine spike that increases the rate of iodine release into the reactor coolant by a factor of 500.
- 2. An assumed reactor coolant concentration of radioactive isotopes with a dose equivalent of 60 Ci/gm of I-131 as a result of preaccident iodine spikes.
- d. The reactor coolant concentrations of noble gas correspond to 1-percent failed fuel.
- e. Partition factors used to determine the secondary system activities are given in Table 15.1-3.
The following specific assumptions and parameters are used to calculate the activity release:
- a. Offsite power is lost, resulting in reactor coolant pump coastdown.
- b. No condenser air removal system release and no normal operating steam generator blowdown is assumed to occur
during the course of the accident.
- c. Eight hours after the occurrence of the accident, the residual heat-removal system (RHRS) starts operation to cool down the plant.
- d. After the accident, the primary-to-secondary leakage continues for 8 hours, at which time the reactor coolant system is depressurized. 15.1-22 Rev. 0 WOLF CREEK
- e. The affected steam generator (steam generator connected to the broken steam line) is allowed to blow down
completely.
- f. Steam release to the atmosphere and the associated activity release from the safety and atmospheric relief valves and the broken steam line is terminated 8 hours after the accident, when the RHRS is activated to complete cooldown.
- g. The amount of noble gas activity released is equal to the amount present in the reactor coolant, which leaks
to the secondary during the accident. The amount of
iodine activity released is based on the activity
present in the secondary system and the amount of leaked reactor coolant which is entrained in the steam that is
discharged to the environment via the safety and atmospheric relief valves and the broken steam line. Partition factors used for the unaffected steam generators after the
accident occurs are given in Table 15.1-3. An iodine partition factor of 1 is used for the affected steam generator.
- h. The activity released from the broken steam line and the safety and atmospheric relief valves during the 8-hour duration of the accident is immediately vented to the atmosphere.
15.1.5.3.1.3 Mathematical Models Used in the Analysis
Mathematical models used in the analysis are described in the following sections: a. The mathematical models used to analyze the activity released during the course of the accident are described in Appendix 15A.
- b. The atmospheric dispersion factors used in the analysis were calculated based on the onsite meteorological measurement programs described in Section 2.3.
- c. The thyroid inhalation dose and total-body gamma immersion doses to a receptor at the exclusion area boundary and outer boundary of the low-population zone
were analyzed, using the models described in Appendix 15A. 15.1-23 Rev. 13 WOLF CREEK 15.1.5.3.1.4 Identification of Leakage Pathways and Resultant Leakage Activity For evaluating the radiological consequences due to a postulated MSLB, the activity released from the affected steam generator (steam generator connected
to the broken steam line) is released directly to the environment. The unaffected steam generators are assumed to continually discharge steam and entrained activity via the safety and atmospheric relief valves up to the time initiation of the RHRS can be accomplished. Since the activity is released directly to the environment with no credit for plateout or retention, the results of the analysis are based on the most direct
leakage pathway available. Therefore, the resultant radiological consequences
represent the most conservative estimate of the potential integrated dose due
to the postulated MSLB. 15.1.5.3.2 Identification of Uncertainties and Conservatisms in the Analysis
- a. Reactor coolant activities are based on the Technical Specification limit of 1.0 Ci/gm I-131 dose equivalent with extremely large iodine spike values persisting for the entire duration of the accident, resulting in equivalent concentrations many times greater than the reactor coolant activities based on 0.12 percent failed
fuel associated with normal operating conditions.
- b. A 1-gpm steam generator primary-to-secondary leakage is assumed, which is significantly greater than that anticipated during normal operation. Furthermore, it
was conservatively assumed that all leakage is to the affected steam generator only.
- c. The meteorological conditions which may be present at the site during the course of the accident are uncertain. However, it is highly unlikely that the
assumed meteorological conditions would be present during the course of the accident for any extended period of time. Therefore, the radiological
consequences evaluated, based on the meteorological conditions assumed, are conservative. 15.1-24 Rev. 13 WOLF CREEK 15.1.5.3.3.1 Filter Loadings The only ESF filtration system considered in the analysis which limits the consequences of the MSLB is the control room filtration system. Activity
loadings on the control room charcoal filter are based on flow rate through the
filter, the concentration of activity at the filter inlet, and the filter
efficiency. Activity in the control room filter as a function of time has been evaluated for the more limiting LOCA analysis, as discussed in Section 15.6.5.4.3.1.
Since the control room filters are capable of accommodating the potential
design basis LOCA fission product iodine loadings, more than adequate design
margin is available with respect to postulated MSLB releases. 15.1.5.3.3.2 Dose to Receptor at the Exclusion Area Boundary and Low-Population Zone Outer Boundary The potential radiological consequences resulting from the occurrence of a postulated MSLB have been conservatively analyzed, using assumptions and models described. The total-body gamma doses due to immersion from direct radiation
and the thyroid dose due to inhalation have been analyzed for the 0-2 hour dose at the exclusion area boundary and for the duration of the accident (0 to 8
hrs) at the low-population zone outer boundary. The results are listed in Table 15.1-4. The resultant doses are within the acceptance limits, a small fraction (10 percent) of exposure limits of 10CFR100, i.e., 2.5 rem and 30 rem respectively for the whole body and thyroid doses for the case of concurrent iodine spike and the exposure limits of 10CFR100 i.e., 25 rem and 300 rem respectively for the whole body and thyroid doses for the case of pre-accident iodine spike. 15.1.5.4 Conclusions The analysis has shown that the criteria stated earlier in Section 15.1.5.1 are satisfied. Although DNB and possible clad perforation following a steam pipe rupture are not necessarily unacceptable and not precluded by the criteria, the above analysis shows that the DNB design basis is met for any rupture, assuming the
most reactive RCCA stuck in its fully withdrawn position. 15.1.5.5 Notes (1) As discussed in Reference 4, the SI response time has an additional delay of 15 seconds. This makes the SI response time 27 and 39 seconds for the cases
with and without offsite power respectively. 15.1-25 Rev. 17 WOLF CREEK 15.
1.6 REFERENCES
- 1. Burnett, T. W. T., et al., "LOFTRAN Code Description," WCAP- 7907-A, April 1984. 2. Moody, F. J., "Transactions of the ASME, Journal of Heat Transfer," Figure 3, page 134, February 1965. 3. Wood, D. C., and Hollingsworth, S. D., "Reactor Core Response to Excessive Secondary Steam Releases," WCAP-9226 (Proprietary), WCAP-9227 (Non-proprietary), January 1978. 4. Letter from D. P. Dominicis, Westinghouse, to O. Maynard, WCNOC, SAP-87-155, "Increased SI Delay Safety Evaluation." April 21, 1987. 5. Paulsen, M.P., et. a1., RETRAN-3D: A Program for Transient Thermal-Hydraulic Analysis of Complex Fluid Flow Systems, EPRI NP-7450(A). July 2001.6. Stewart, C. W., et. al.,"VIPRE-01: A Thermal-Hydraulic Code for Reactor Cores," Battelle, Pacific Northwest Laboratories, EPRI NP-2511-CCM-A, August 1989. 15.1-26 Rev. 22 TABLE 15.1-1 TIME SEQUENCE OF EVENTS FOR INCIDENTS THAT RESULT IN AN INCREASE IN HEAT REMOVAL BY THE SECONDARY SYSTEM Time Accident Event (sec)Feedwater system malfunctions that
result in an increase in feedwater flow at full power Two main feedwater control 0.0
valves fail fully open Feedwater Isolation due 28.7 to high-high steam
generator level Reactor trip on lo-lo 57.9 steam generator level Rods begin to drop 59.9
Minimum DNBR occurs 36.0 Excessive increase in secondary steam flow
- 1. Manual reactor 10-percent step load 0.0 control (minimum increase
moderator feedback) Equilibrium conditions 140 reached (approximate
time only)
- 2. Manual reactor 10-percent step load 0.0 control (maximum increase
moderator feedback) Equilibrium conditions 50 reached (approximate time
only)
- 3. Automatic reactor 10-percent step load 0.0 control (minimum increase
moderator feedback) Equilibrium conditions 110 reached (approximate
time only)
- 4. Automatic reactor 10-percent step load 0.0 control (maximum increase moderator feedback)
Equilibrium conditions 50 reached (approximate time only) Rev. 22 TABLE 15.1-1 (Sheet 2) Time
Accident Event (sec)
Inadvertent opening of
a steam generator atmo-
spheric relief or safety
valve
Inadvertent opening of 0.0
one main steam safety
or atmospheric relief valve
Auxiliary Feedwater
Actuation 0.0
Low Pressure Trip (SIS) 185
Peak Reactor power 372
RWST boron solution 400
reaches core
Steam system piping
failure
- 1. Case 1 (offsite Steam line ruptures 0.0
power available) Low steam line pressure 0.89 setpoint reached Steam line isolation 2.97 begins Steam line isolation 17.97 complete, feed line isolation SI begins 52.97 Peak core thermal 144.00 power occurs Minimun DNBR occurs 149.6
- 2. Case 2 (concurrent Steam line ruptures 0.0
loss of offsite
power) SI actuation 18.0
Criticality attained 22.0
Pressurizer empties 18.0
RWST boron solution 82.0 reaches core
Rev. 29 WOLF CREEK TABLE 15.1-2
EQUIPMENT REQUIRED FOLLOWING A RUPTURE OF A MAIN STEAM LINE Short-Term (Required for Mitigation of Accident) Hot Standby Required for Cooldown Reactor trip and safeguard Auxiliary feedwater system, Steam generator atmospheric actuation channels, including including pumps, water supply relief valves sensors, circuitry, and pro- steam generator atmospheric
cessing equipment (the pro- relief valves and system valves Control for defeating automatic tection circuits used to trip and piping (this system must safety injection actuation dur-the reactor on undervoltage, be placed in service to supply ing a cooldown and depressuri-underfrequency, and turbine water to operable steam genera- zation (i.e., SIS is reset)
trip may be excluded) tors no later than 10 minutes
after the incident) Safety injection system, Containment air coolers Residual heat removal system, including the pumps, the including pumps, heat refueling water storage tank, exchanger, and system valves the boron injection tank, and Capability for obtaining and piping necessary to cool the system valves and piping reactor coolant system sample and maintain the reactor coolant system in a cold shutdown condition Containment spray system Capability for boration to Capability to depressurize required hot standby concen- the reactor coolant system tration to allow residual heat removal system operation Diesel generators and emergency power distribution
equipment Essential service water system
Containment air coolers Rev. 11 WOLF CREEK
TABLE 15.1-2 (Sheet 2)
Short-Term (Required for Mitigation
of Accident) Hot Standby Required for Cooldown
Auxiliary feedwater system, including pumps, water sup-
plies, piping and valves
Main feedwater control valves (trip closed feature)
Bypass feedwater control
valves (trip closed feature)
Primary and secondary safety Capability to borate to
valves cold shutdown concentration
Associated pump room coolers
Main feedwater isolation
valves (trip closed feature)
Main steamline isolation
valves (trip closed feature)
Main steamline isolation
valve bypass valves (trip
closed feature)
Steam generator blowdown
isolation valves (auto-
matic closure feature)
Batteries (Class 1E)
Rev. 27 WOLF CREEK TABLE 15.1-2 (Sheet 3) Short-Term (Required for Mitigation of Accident) Hot Standby Required for Cooldown Control room ventilation Control room equipment must not be damaged to an extent where any equipment will be
spuriously actuated or any of the equipment contained elsewhere in this list can-not be operated. Emergency lighting
Post-accident monitoring system**See Section 7.5 for a discussion of the post-accident monitoring systems. Rev. 0 WOLF CREEK TABLE 15.1-3 PARAMETERS USED IN EVALUATING THE RADIOLOGICAL CONSEQUENCES OF A MAIN STEAM LINE BREAK I. Source Data: a. Core power level, Mwt 3565 b. Steam generator tube leakage, gpm 1
- c. Reactor coolant iodine activity: 1) Case 1 Dose equivalent of 1.0 Ci/gm of I-131 with an assumed iodine spike that increases the rate of iodine release into the reactor coolant by a factor of 500 2) Case 2 An assumed pre-accident iodine spike which has resulted in the dose equivalent of 60 Ci/gm of I-131 d. Reactor coolant noble gas activity: 1) Case 1 Based on 1-percent failed fuel as provided in Table 11.1-5 2) Case 2 Based on 1-percent failed fuel as provided in Table 11.1-5 e. Secondary system initial Dose equivalent of 0.1 Ci/gmactivity of I-131 f. Iodine partition factors 1) Affected steam generator 1.0 2) Unaffected steam generator 0.01 g. Reactor coolant mass, lbs 4.94E+5 h. Steam generator mass 1) Affected steam generator, lbs 164,500 2) Each unaffected steam generator, lbs 95,500 II. Atmospheric Dispersion Factors See Table 15A-2 III. Activity Release Data: a. Affected steam generator 1) Initial steam release, 0-30 min, lbs 164,500 2) Reactor coolant release, 0-8 hr, lbs 4,000 b. Unaffected steam generator 1) Steam release, 0-2 hr, lbs 404,452 2) Steam release, 2-8 hr, lbs 945,973 3) Reactor coolant release, 0-8 hr, lbs 0 Rev. 13 WOLF CREEK TABLE 15.1-3 (Sheet 2) c. Activity released to the environment 1) Case 1 Isotope 0-2 hr (Ci) 0-8 hr (Ci)I-131 2.45E+1 3.00E+2 I-132 5.81E+1 2.99E+2 I-133 5.01E+1 5.69E+2 I-134 1.66E+1 3.32E+1 I-135 3.73E+1 3.48E+2 Xe-131m 1.54 6.11 Xe-133m 2.40 9.23 Xe-133 1.31E+2 5.13E+2 Xe-135m 5.13E-2 5.15E-2 Xe-135 4.13 1.33E+1
Xe-137 4.68E-3 4.68E-3
Xe-138 6.29E-2 6.31E-2
Kr-83m 1.76E-1 3.14E-1 Kr-85m 8.81E-1 2.34 Kr-85 4.27 1.70E+1 Kr-87 4.06E-1 6.03E-1 Kr-88 1.53 3.39 Kr-89 2.09E-3 2.10E-3 2) Case 2
Isotope 0-2 hr (Ci) 0-8 hr (Ci)I-131 2.54E+1 8.41E+1 I-132 2.30E+1 4.01E+1 I-133 4.37E+1 1.33E+2 I-134 4.17 4.86 I-135 2.43E+1 6.21E+1 Xe-131m 1.54 6.11 Xe-133m 2.40 9.23 Xe-133 1.31E+2 5.13E+2 Xe-135m 5.13E-2 5.15E-2 Xe-135 4.13 1.33E+1
Xe-137 4.68E-3 4.68E-3
Xe-138 6.29E-2 6.31E-2
Kr-83m 1.76E-1 3.14E-1 Kr-85m 8.81E-1 2.34 Kr-85 4.27 1.70E+1 Kr-87 4.06E-1 6.03E-1 Kr-88 1.53 3.39 Kr-89 2.09E-3 2.10E-3 Rev. 17 WOLF CREEK TABLE 15.1-4
RADIOLOGICAL CONSEQUENCES OF A MAIN STEAM LINE BREAK Dose (rem) CASE 1 , 1.0 Ci/gm I-131 equivalent w/I spike Exclusion area boundary (0-2 hr) Thyroid 2.76 Whole body 9.98E-3 Low-population zone outer
boundary (duration)
Thyroid 4.33 Whole body 8.78E-3 CASE 2 , 60 Ci/gm I-131 equivalent Exclusion area boundary (0-2 hr) Thyroid 2.67
Whole body 5.34E-3 Low population zone outer boundary (duration)
Thyroid 1.15 Whole body 1.69E-3 Rev. 17 !'J I '"1 ... lit '8 0 I ... . 0 ... Ill I 0 I ., 0 :lo I s I L !: j I I J I 10 80 'Rne(IIC) 40 80 Tlme(IIC) 8D 100 8D 100 Rev. 10 WOLFCREEK UPDA'IFD SAmY ANALYSIS IU!JIOI.T PIGUim 15.1-l NUCLEAilPOWER, AND PRESS1.JRIZEil PRESSURE mANSIENTS FOR FEEDWA'IER. CONTROL VAL VB MALFUNCDON ...... LL .... .I c! a. 8 _, I I I 'II i I 8 I!! II II Ill a s
- 0
- liD llme(sec)
Rev. 10 WOLPCREIIK UPDA'IED SAFETY ANALYSIS REPOR.T FIGUIUI 15.1-2 R.EACTOR. COOLANT LOOP AT. ANDCORBHBATPWX TRANSIENTS FOa PEIDWA11!R. CONTROL VAL VB MAI.IItJNCTJON I 2 I co 8 ! I I c ... -I tD J c I ! 0 C) §! 0 20 .a 60 80 100 Tlnw(IIC) 3.10 2.10 1.110 ****** Dellgn Linl *---------**-*********----***-****************** 1.70 ....,_ ___ ...,.. ___ _.., _____ ,.._ __ ....,_ __ --+ ____ .....,. 0.0 10.0 20.0 80.0 Re¥.13 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 11.1*2A CORE AVERAGE TEIIPERATURE TRANSIENT AND MINIMUM DNBR FOR FEEDWATER CONTROL VALVE MALFUNCTION
- L ,,. I '
- o.e 1-I o-*1-I o.* l.o.. 1-00 110 tOO , .. zoo-... **aoo I**'-"'
'*--1-1.aoo 0 -,GO ,_ :100 ,,zoo------------------------ l*.ooo: I *- I ... I '100 *- .. ftYC (UCIIIIII., Rev. ? WOLP CRBB1t OPDATBD SAFETY ANALYSIS REPORT PIOURB 1!5.1-3 NtJCLBAR POWBR, PRESSURB AND WA'rBJl VOLOMB TRANSIENTS FOR TE1f PERCBN'l' STEP LOAD INCRRASB MIRIMOM REACTIVITY PBBDBACIC, MANUAL REACTOR CONTROL 2.llt II: = ..... 0 I I
- 2.U a .a II tOO , .. liD . .. , .... , ....... , 598r----------------------------------------------,
,... (SECONDS) Rev. 1 WOLP CRBBlt tJPDATBD SAPBTr AHALYSIS RBPORT FIGURB 15.1-4 DNBR Aim VBSSBL AVBRAOB TBMPBRATORB TRUSIBR'l'S POR 'I'D PBRCER'l' S'l'BP LOAD IHCRBASB, MINIMUM REACTIVITY PBBDBAClt, MANtJAL REACTOR COBTROL ..* ------------------------, ,./ *o.er-t ... 1-r-lo.a* 0.o!:-----:!r .. ---::-=----,:,.1 .. =-----';:f. ---...... . -.-. , .. _ .. I.AOO **-I-'-o . .-'**-***-. I --I -I 700 .. tOO ... aoo *-. ... Rev. 1 WOLP CRBBJC UPDATED SAPBTY ARALYSIS RBPOR'l' PIGURB 15.1-5 Rt1CLBAR POWBR, PRBSSURIZBR PRBSStJRB AND D.TBR VOLtJMB TIWfSID'l'S . JOR '1'JD1 PBilCBNT STD LOAD INCRBASB MAXIMCM RBAC'IIVITY FBBDBAClt, MARtJAL RBACTOR CON'l'ROL J.ll r------------------------.
- 1.1 Ul = 1.! I I ' u.* J-11 J
__ _. _____ I II tot til IM HI .. 515 c:"MO i. i'.... s*r-I""'" 570 1-moat-so n.eet....._, . 100 110 200 TIME (SECONDS) Rev. 7 WOLP CRERit UPDATBD SAPB'1'!' ANALYSIS RBPORT PICKJRB 15.1*6 DHBR AND VBSSBL AVBRAGB TBMPBRATORB TRAHSIDTS FOR TBII PBRCBli1T STBP LOAD DfcRusB, MIBIMtlM RSACTIVI'l'r PBJII)IACK, MAHtJAL R.BACTOR CON'l'ROL , .* I , ' -... 100 ,.... aoo *--...... --------------------t IL1DO !-1 .. t,.OO !-'*- .,.... c*oa lila) ., __ I --1: ... .. .,.... twsaa IllS) Rev. ? WOLP CRBBK UPDATBD SAPB'l'Y ANALYSIS RBPORT PIGURB 15.1-7 NUCLBAR POWBR, PRBSStJRIZBR PRBSSORB AND WATER VOLUMB TRANSIDTS FOR ftR PBRCBNT S'l'BP LOAD INCRBASB MDmmM RIACTIVITY PBBDBACit, AUTOMATIC RBACTOR c.u&'l'ROL
... I .II * = ... * ! J 1.11 * * ... 1-.... 1-I 1-*. ______ _. ______ I II Ill til IH Ill -595 'C:'HO .. 1-" NO!-I S715 !-570 !-mHS MOo*
- 10 n ** ..., ..... , . 100 150 2GO zso 1M: (SECONDS)
Rev. 7 WOLF CRBBtt UPDATID SAPB"l'Y ARALYSIS RBPOR'l' FIGURB 15.1-8 DNBR UD VBSSBL AVBRAGB TDJPBRA'l'URB TIWfSIBRTS FOR 'l'Blf PBRCBII'r S'l'BP LOAD IHCRBASB, MIH'IMOM RBACTIVITY FBBDBACIC, AO'l'OMATIC REACTOR t'OM'l'ROL
I , v-* ca .. r ( ... r lo .. r
- -,----------------------------, l*.uo.
1..-. **-.. f ..... tr-----------------------1 l*.-ar I '1'00 -* 1 TNE c.:C8f11 .. ., -** aoo Rev. ? WOLP CRBB1It OPDATBD SAPB'1'Y ANALYSIS RBPORT PIGORB 15.1-9. NUCLBAR POWBR, PRBSSURIZBR PRBSSORB AND WATBR VOLUMB TRARSIBIITS POR TBR PBRCBR'l' . STBP LOAD I&CRBASB MUIMOM RBAC'l'IVITY FBBDBACK, AD'l'OMM'IC RBAC'l'OR CX>RTR.OL
- ... * **** -* *
- 1-* ... * * * .... -* t.t r-.... -* * ** n* ;;:" SIO I t=" I :17:1-570 1-Waa-5800 I Ut 100 ... * ** ... .. . , ... c ....... , .L 150 200 :..0 TIMI (SECONDS)
Rev. 7 WOLF CRBRK UPDATED SAPETY ANALYSIS REPORT PIGORB 15.1*10 DRBR AND VBSSBL AVBRAGB TBMPDATtJRB TRANSIBN'l'S POR TBH PBRCBN'l' STBI? LOAD IRCRBASB, MAXIMUM REACTIVITY PBBDBAClt, RBACTOR CONTROL ... 1.03 ... w ¥: 1.02 0 :K 0 .... 1.01 cj --i 1.00 0.99 O.H __ ___ 200 250 300 350 500 550 600 COOWT AVERAGE TEMPERA lURE WOLI' OPDAUD 8U'IIft UU.YSIS RDOft Rev. 0 FIBURE 15.1-11 K£ff VERSUS T£HP£RATURE
REV.29 WOLFCREEKUPDATEDSAFETYANALYSISREPORTFIGURE15.1 11a:K effVersusTemperatureSLBwithOffsitePower 1.2 -v I , e o.e I a.* :-! 0.4 1-I 0.2 1-00 100 200 300 *oo aoo 800 "700 eoa P-I sao -400 1300 1-g2oo -v 100 1-1-' 00 I
- 100 zoo 300 *oo 800 500 0 I I (500) ( 1,000) (1.500) 0 100 200 300 TIWE (ti&CONOa) 4-00 aoo eoo Rev.13 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 11.1*12 FAILURE OF A ITEAM GENERATOR 8AFErY ORATIIOIPHERIC v RELIEF VALVE 2.400 2.200 ! 2.000 I 1,800 I 1,500 1,400 1,200 1.000 0 100 200 300 400 eoo 700 -=-600 .... a ...... 500 400
- 300 ; 200 100 100 200 300 400 500 eoo 50 40 -2 a ; 20 c,.)
TIME CSECONDS) Rev.14 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.1-13 FAILURE OF A STEAM GENERATOR SAFETY OR ATMOSPHERIC RELIEF VALVE -e u a. -..... c.J ..... 1.&. ..... Q (,) Gil ...... ! ct. ..... g oC cz: (!) .... 1000 __________ __ 0 I 0 20 30 IW 50 60 aev. 0 CORE POWER (PERCENT\ wou OI'D&HD* 8U'ft'f ua.L'fSIS UPOJft' FIGURE 15.1 .. 14 DOPPLER POWER FEEDBACK .v REV.29 WOLFCREEKUPDATEDSAFETYANALYSISREPORTFIGURE15.1 15:NormalizedCorePowerandNormalizedCoreHeatFluxSLBwithOffsitePower REV.29 WOLFCREEKUPDATEDSAFETYANALYSISREPORTFIGURE15.1 16:PressurizerPressureandPressurizerLiquidVolumeSLBwithOffsitePower REV.29 WOLFCREEKUPDATEDSAFETYANALYSISREPORTFIGURE15.1 17:CoreInletTemperatureandCoreAverageTemperatureSLBwithOffsitePower REV.29 WOLFCREEKUPDATEDSAFETYANALYSISREPORTFIGURE15.1 18:TotalCoreReactivityandCoreBoronConcentrationSLBwithOffsitePower REV.29 WOLFCREEKUPDATEDSAFETYANALYSISREPORTFIGURE15.1 19:NormalizedFeedwaterFlowandBreakFlowSLBwithOffsitePower REV.29 WOLFCREEKUPDATEDSAFETYANALYSISREPORTFIGURE15.1 20:SteamlinePressureandCoreInletFlowSLBwithOffsitePower
REV.29 WOLFCREEKUPDATEDSAFETYANALYSISREPORTFIGURE15.1 20a:SLBTransientatHot ZeroPowerwithoutoffsitePowerAvailableAdjMinimumDNBRvsTime
- (__, 0.1 0.08 B _o.04 0.02 00. 0.1 L, 0.08 l ! 0.08 I.L I o.04 § (J 0.02 --...
40 80 80 100 120 140 Tlme(aec) 20 40 60 80 100 lime(sec) Rev. 7 1fOLP CRBlllt UPDATED SAFB'n' ARALYSIS RBPORT
- PIGURB 15.1-21a NORMALIZED COU POWBR ARD NORMALIZED CORB BEAT PLtJX SLB 1fiTHOOT OFFSITB P0W11t
- I
,12.000. ! 1.800 11.600 Q. .1,400 a: 1.200 1*000 llme(aec) llma(sec) WOLP CUBK Re¥.7 OPDATBD SAFBTY ARALYSiS RDORT PIGORB 15.1-22:: PRBSSORIZBR. PRBSSORB AND PRBSSURIZIR Ll:QtJID :voLtJMB SLB WITHOUT OI'PSITB POWBR.
F ........ --.... -... ..... i .400 ------------- 8 *-*-*-* 0 3500 I I 20 40 eo 80 100 120 140 .11me (sec) 570 [680 1550 &540 GJ rs20 510 c§soo 4900 20 eo 80 100 120 140 11me(sec) WOLP CRBBK Rav.7 UPDATBD SU'BTr AHALYSIS .RBPORT PIGDRB 15.1-23a COR& IHLBT TBMPBRA'l'DRB AND CORB AVBRAGB TBMPBKATORB SLB WITHOUT OPFSITB POWBR
I 1:1 J (500) I! 8 .(1,000) <1*500> ......... llme (sec) WOLP CRIBit Rev. 7 UPDATRD SAFRTY ANALYSIS REPORT PIGORB 15.1-24s 'l'OTAL CORB RBACTIVITY AND CORB BOROR CONCBN'tkATION SLB WITHOtJT OPPSITB POWER 1.2 r--1 -c. g 0.8 1 0.8 I j.o.4 u. I 0.2 ' 00 20 40 eo so 100 120 140 llme(sec) FIUitlld Loap lnlllct Loap 2.5 -c 2 g 2 ii: 1.5 J 1 CIJ 0.5 0 o 20 40 eo 8o 100 120 140 llrne(aec) Rev.7 WOLP CRBB1t UPDATBD SAPB'1'! ANALYSIS REPORT P'IOURB 15.1-25: NORMALIZED P'BBDWATBR FLOW AND BRBA1t FLOW SLB WITHCroT OP'PSI'l'B POWER 1,400.-----------------..., 1,200 -t 1,000 -j: * * ' 1-400" ' ' 200 ' ' .. .. .. .... .... --.... -... 11me(eec) 1.2 r-------------------, 1 1 o.a -1 0.8 u. ! a o.4 0.2 00 100 Tme(eec) WOLP CRBB1t Rev.7 UPDATBD SAPR'rY ANALYSIS RBPORT . PIGORB 15.1-26: STBAMLDJB PRBSstJRB ARD CORB INLBT PLOW SLB WITHOUT OFFSITB POWBR WOLF CREEK 15.2 DECREASE IN HEAT REMOVAL BY THE SECONDARY SYSTEM A number of transients and accidents have been postulated which could result in a reduction of the capacity of the secondary system to remove heat generated in the reactor coolant system (RCS). Detailed analyses are presented in this section for the following events, which have been identified as more limiting than the others:
- a. Steam pressure regulator malfunction or failure that results in decreasing steam flow
- b. Loss of external electrical load
- c. Turbine trip
- d. Inadvertent closure of main steam isolation valves
- e. Loss of condenser vacuum and other events resulting in turbine trip
- f. Loss of nonemergency ac power to the station auxiliaries
- g. Loss of normal feedwater flow
- h. Feedwater system pipe break
The above items are considered to be ANS Condition II events, with the exception of a feedwater system pipe break, which is considered to be an ANS
Condition IV event. Section 15.0.1 contains a discussion of ANS
classifications and applicable acceptance criteria. All of the accidents in this section have been analyzed. It has been determined that the most severe radiological consequences will result from the loss of ac power accident of Section 15.2.6. Therefore, the radiological
consequences are only reported for that limiting case. 15.2.1 STEAM PRESSURE REGULATOR MALFUNCTION OR FAILURE THAT RESULTS IN DECREASING STEAM FLOW There are no steam pressure regulators in the Wolf Creek unit whose failure or malfunction could cause a steam flow transient. Therefore, this event is not applicable to the Wolf Creek Generating Station. 15.2-1 Rev. 7 WOLF CREEK 15.2.2 LOSS OF EXTERNAL ELECTRICAL LOAD 15.2.2.1 Identification of Causes and Accident Description A major load loss on the plant can result from loss of external electrical load due to some electrical system disturbance. Offsite ac power remains available to operate plant components, such as the reactor coolant pumps; as a result, the onsite emergency diesel generators are not required to function for this event. Following the loss of generator load, an immediate fast closure of the turbine control valves will occur. The automatic turbine bypass system would accommodate the excess steam generation. Reactor coolant temperatures and pressure do not significantly increase if the turbine bypass system and pressurizer pressure control system are functioning properly. If the condenser
were not available, the excess steam generation would be relieved to the atmosphere. Additionally, main feedwater flow would be lost if the condenser were not available. For this situation, feedwater flow would be maintained by
the auxiliary feedwater system. For a loss of external electrical load without subsequent turbine trip, no direct reactor trip signal would be generated. The plant would trip from the reactor protection system if a safety limit were approached. A continued steam
load of approximately 5 percent would exist after total loss of external
electrical load, because of the steam demand of plant auxiliaries. Following the loss of load, protection would be provided by high pressurizer pressure, high pressurizer water level, and overtemperature DT trips should a
safety limit be approached. Voltage and frequency relays associated with the
reactor coolant pump provide no additional safety function for this event.
Following a complete loss of external load, the maximum turbine overspeed would
be approximately 8 to 9 percent, resulting in an overfrequency of less than 6
Hz. This resulting overfrequency is not expected to damage the voltage and
frequency sensors in any way. Any degradation in their performance could be
ascertained at that time. Any increased frequency to the reactor coolant pump
motors will result in slightly increased flow rate and subsequent additional
margin to safety limits. For postulated loss of load and subsequent turbine-generator overspeed, any overfrequency condition is not seen by other safety-
related pump motors, reactor protection system equipment, or other safety-related loads. Safety-related loads are supplied from offsite power or, alternatively, from emergency diesels. Reactor protection system equipment is supplied from the 120-Volt ac instrument power supply system which, in turn, is supplied from the inverters; the inverters are supplied from a dc bus energized from batteries or by a rectified ac voltage from safety-related busses. 15.2-2 Rev. 12 WOLF CREEK In the event that the turbine bypass valves fail to open following a large loss of load, the steam generator safety valves may lift, and the reactor may be
tripped by the high pressurizer pressure signal, the high pressurizer water level signal, or the overtemperature DT signal. The steam generator shell side pressure and reactor coolant temperature will increase rapidly. The pressurizer
safety valves and steam generator safety valves are, however, sized to protect the RCS and steam generator against overpressure for all load losses without assuming the operation of the turbine bypass system, pressurizer spray, pressurizer power-operated relief valves, automatic rod cluster control assembly (RCCA) control, or direct reactor trip on turbine trip. The steam generator safety valve capacity is sized to remove the steam flow at the engineered safety features rating (see section 5.2.2.1) from the steam generator, without exceeding 110 percent of the steam system design pressure. The pressurizer safety valve capacity is sized to accommodate a complete loss of heat sink, with the plant initially operating at the maximum calculated turbine load along with operation of the steam generator safety valves. The
pressurizer safety valves are then able to relieve sufficient steam to maintain the RCS pressure within 110 percent of the RCS design pressure. A more complete discussion of overpressure protection can be found in Reference 1.A loss of external load is classified as an ANS Condition II event, fault of moderate frequency. See Section 15.0.1 for a discussion of Condition II events.A loss of external load event results in a nuclear steam supply system transient that is bounded by the turbine trip event analyzed in Section 15.2.3. Therefore, a detailed transient analysis is not presented for the loss of
external load event. The primary side transient is caused by a decrease in heat transfer capability from primary to secondary, due to a rapid termination of steam flow to the
turbine, accompanied by an automatic reduction of feedwater flow (should
feedwater flow not be reduced, a larger heat sink would be available and the
transient would be less severe). Termination of steam flow to the turbine
following a loss of external load occurs due to automatic fast closure of the
turbine control valves. Following a turbine trip event, termination of steam flow occurs via turbine stop valve closure (see section 10.2.2.2). The analysis performed for the turbine trip event assumes an instantaneous loss of steam flow, therefore, the transient in primary pressure, temperature, and water volume will be less severe for the loss of external load than for the turbine trip, due to a slightly slower loss of heat transfer capability. 15.2-3 Rev. 12 WOLF CREEK The protection available to mitigate the consequences of a loss of external load is the same as that for a turbine trip, as listed in Table 15.0-6. 15.2.2.2 Analysis of Effects and Consequences Refer to Section 15.2.3.2 for the method used to analyze the limiting transient (turbine trip) in this grouping of events. The results of the turbine trip event analysis bound those expected for the loss of external load, as discussed in Section 15.2.2.1. Plant systems and equipment which may be required to function to mitigate the effects of a complete loss of load are discussed in Section 15.0.8 and listed in Table 15.0-6. The reactor protection system may be required to function to terminate core heat input and to prevent departure from nucleate boiling (DNB). Depending on
the magnitude of the load loss, pressurizer safety valves and/or steam
generator safety valves may be required to open to maintain system pressures
below allowable limits. No single active failure will prevent operation of any
system required to function. Normal reactor control systems and engineered
safety systems are not required to function. The auxiliary feedwater system
may, however, be automatically actuated following a loss of main feedwater;
this will further mitigate the effects of the transient. 15.2.2.3 Conclusions Based on results obtained for the turbine trip event (see Section 15.2.3) and considerations described in Section 15.2.2.1, the applicable acceptance
criteria for a loss of external load event are met. 15.2.3 TURBINE TRIP
15.2.3.1 Identification of Causes and Accident Description For a turbine trip event, the reactor would be tripped directly (Direct reactor trip on turbine trip is blocked below 50% power by the P-9 interlock) from a signal derived from the turbine stop emergency trip fluid pressure and turbine
stop valves. The turbine stop valves close rapidly (see section 10.2.2.2) on loss of trip fluid pressure actuated by one of a number of possible turbine trip signals. Turbine trip initiation signals include: 15.2-4 Rev. 12 WOLF CREEK
- a. Generator trip
- b. Low condenser vacuum
- c. Loss of lubricating oil
- d. Turbine thrust bearing failure
- e. Turbine overspeed
- f. Manual trip Upon initiation of stop valve closure, steam flow to the turbine stops abruptly. Sensors on the stop valves detect the turbine trip and initiate
turbine bypass, and, if above 50-percent power, a reactor trip. The loss of
steam flow results in an almost immediate rise in secondary system temperature
and pressure, with a resultant primary system transient as described in Section
15.2.2.1 for the loss of external load event. A slightly more severe transient may occur for the turbine trip event, due to the more rapid loss of steam flow caused by the more rapid valve closure (see section 10.2.2.2), hence a more rapid loss of primary-to-secondary heat transfer. The automatic turbine bypass system would accommodate up to 40 percent of rated steam flow. Reactor coolant temperatures and pressure do not increase significantly if the turbine bypass system and pressurizer pressure control system are functioning properly. If the condenser were not available, the
excess steam generation would be relieved to the atmosphere, and main feedwater
flow would be lost. For this situation, feedwater flow would be maintained by the auxiliary feedwater system to ensure adequate residual and decay heat removal capability. Should the turbine bypass system fail to operate, the steam
generator safety valves may lift to provide pressure control. See Section
15.2.2.1 for a further discussion of the transient. A turbine trip is classified as an ANS Condition II event, fault of moderate frequency. See Section 15.0.1 for a discussion of Condition II events. A turbine trip is more limiting than loss of external load, loss of condenser vacuum, and other events which result in a turbine trip as a result of the potential for a more rapid loss of steam flow during the turbine trip. As such, this event has been analyzed in detail. Results and discussion of the analysis are presented in Section 15.2.3.2. 15.2.3.2 Analysis of Effects and Consequences Method of Analysis In this analysis, the behavior of the unit is evaluated for a complete loss of steam load from 102 percent of full power, without direct reactor trip, primarily to show the adequacy of the pressure relieving devices, and also to demonstrate core protection margins; that is, the turbine is assumed to trip 15.2-5 Rev. 12 WOLF CREEK without actuating all the sensors for reactor trip on the turbine stop valves. This assumption delays reactor trip until conditions in the RCS result in a
trip due to other signals. Thus, the analysis assumes a worst transient. In addition, no credit is taken for the turbine bypass system. Main feedwater flow is terminated at the time of turbine trip, with no credit taken for auxiliary
feedwater to mitigate the consequences of the transient. The turbine trip transients are analyzed by employing the detailed digital computer program RETRAN-02 (Ref 5). RETRAN-02 has been found acceptable by the NRC for use as a licensing basis safety analysis code. RETRAN-02 is a thermal-hydraulic systems analysis code employing a one-dimensional, homogeneous
equilibrium mixture thermal-hydraulic model for the RCS, a point kinetics model
for the reactor core, special component and auxiliary models (ex., pumps, temperature transport, non-equilibrium pressurizer) and control system models.
The code computes pertinent plant transient information including core power
level, RCS pressure and temperature. VIPRE-01 (Ref 6) is used to evaluate the
core thermal limits to determine DNBR. RETRAN-02 generated state points are
used as VIPRE-01 boundary conditions to perform a Statistical Core Design (SCD) DNB analysis. The turbine trip event is analyzed for RCS overpressurization assuming nominal initial conditions including allowances for measurement errors. DNBR is evaluated using Westinghouse RTDP methodology (Ref. 7) which assumes nominal
initial conditions. The major assumptions used in the analysis are summarized below: a. Initial operating conditions (Overpressure) Initial reactor power and RCS temperatures are assumed at their maximum values consistent with steady state full power operation, including allowances for calibration and instrument errors. The
initial RCS pressure is assumed at a minimum value consistent with
steady state full power operation, including allowances for
calibration and instrument errors. This is to maximize the heat up
time prior to reactor trip and therefore, maximizing the peak RCS
pressure and peak pressurizer level during the transient. b. Initial operating conditions (DNB) The initial pressure, reactor power and RCS temperatures are assumed at their nominal values consistent with steady state full power operation. Allowances for calibration and instrument errors are treated statistically by the DNBR evaluation code. 15.2-6 Rev. 12 WOLF CREEK c. Reactivity coefficients (two cases are analyzed): 1. Minimum reactivity feedback A most positive moderator temperature coefficient and a least negative Doppler-only power coefficient are assumed. 2. Maximum reactivity feedback A conservatively large negative moderator temperature coefficient and a most negative Doppler-only power
coefficient are assumed. Cases for DNB and system overpressurization are analyzed for both the minimum and maximum reactivity feedback conditions. d. Reactor control From the standpoint of the maximum pressures attained, it is conservative to assume that the reactor is in manual control.
If the reactor were in automatic control, the control rod
banks would move prior to trip and reduce the severity of the
transient. e. Steam release No credit is taken for the operation of the turbine bypass
system or steam generator atmospheric relief valves. The steam generator pressure rises to the safety valve setpoint where steam release through safety valves limits secondary
steam pressure at the setpoint value. f. Pressurizer spray and power-operated relief valves 1. DNB Full credit is taken for the effect of pressurizer spray and power-operated relief valves in reducing or limiting the coolant pressure. Safety valves are also available. 2. Overpressure No credit is taken for the effect of pressurizer spray and
power-operated relief valves in reducing or limiting the
coolant pressure. Safety valves are operable. g. Feedwater flow Main feedwater flow to the steam generators is assumed to be
lost at the time of turbine trip. No credit is taken for
auxiliary feedwater flow, since a stabilized plant condition will be reached before auxiliary feedwater initiation is normally assumed to occur; however, the auxiliary feedwater
pumps would be expected to start on a trip of the main
feedwater pumps. The 15.2-7 Rev. 11 WOLF CREEK auxiliary feedwater flow would remove core decay heat following plant stabilization. h. Reactor trip is actuated by the first reactor protection system trip setpoint reached, with no credit taken for the direct reactor
trip on the turbine trip. Trip signals are expected due to high pressurizer pressure, overtemperature T, and low-low steam generator water level. Plant characteristics and initial conditions are further discussed in Section 15.0.3.Major plant systems and equipment available for mitigation of transient and accident conditions which may be required to function to mitigate the effects of a turbine trip event are discussed in Section 15.0.8 and listed in Table 15.0-6. The actual parameters assumed and results are given in the respective section/subsection. Table 15.0-6 incorporates events shown in the sequence diagram, Figure 15.0-11. The reactor protection system may be required to function following a turbine trip. Pressurizer safety valves and/or steam generator safety valves may be
required to open to maintain system pressures below allowable limits. No single active failure will prevent operation of any system required to function. Normal reactor control system and engineered safety systems are not
required to function. Results The transient responses for a turbine trip from 102 percent of full power operation are shown for four cases in Figures 15.2-1 through 15.2-8. Two cases
are presented without pressure control (i.e., PORVs, pressurizer spray) to ensure 110% of the design pressure (2750 psia) is not exceeded and two cases using nominal initial plant conditions and pressure control are analyzed to
provide boundary conditions for DNB analysis. Each case is analyzed assuming
minimum and maximum reactivity feedback to ensure the worst case is analyzed.
The calculated sequence of events for the accident is shown in Table 15.2-1. Figures 15.2-1 and 15.2-2 show the transient responses for the total loss of steam load overpressure evaluation with minimum reactivity feedback, assuming no credit is taken for the steam bypass. The reactor is tripped on the high
pressurizer pressure signal. The neutron flux increases slightly above 102
percent of full power until the reactor is tripped, due to the positive
moderator temperature coefficient. In this case, the pressurizer safety valves
are actuated, and maintain RCS pressure below 110 percent of the design value. Figures 15.2-3 and 15.2-4 show the responses for the total loss of steam load overpressure evaluation with maximum reactivity feedback. All other plant parameters are assumed to be the same as in the previous case. Again, the
reactor is tripped on high pressurizer pressure and the pressurizer safety valves are actuated to limit primary pressure. 15.2-8 Rev. 13 WOLF CREEK The DNB evaluation for the turbine trip event was analyzed assuming full pressure control and nominal initial conditions. The errors in initial
conditions are treated statistically in the VIPRE model (Ref 5). Figures 15.2-5 and 15.2-6 show the transient responses for the total loss of steam load with minimum reactivity feedback for the DNB evaluation. No credit is taken for the
steam bypass. Due to the positive moderator temperature coefficient, the power increases to approximately 110 percent of nominal before the reactor is tripped by the high pressurizer pressure trip channel. Steam is released through the pressurizer safety valves for this case and the maximum RCS pressure is maintained below 110 percent of the design pressure. The steam generator
safety valves limit the secondary steam conditions to saturation at the safety valve setpoint. Minimum DNBR remains above the safety analysis limit. Figures 15.2-7 and 15.2-8 show the response for the DNB evaluation with maximum reactivity feedback. The reactor is tripped by the high pressurizer pressure
trip channel but the pressurizer safety valves are not actuated for this case. Reactor power remains essentially constant until the trip occurs. The steam generator safety valves limit the secondary steam conditions to saturation at the safety valve setpoint. Minimum DNBR remains above the safety analysis limit.Reference 1 presents additional results of analysis for a complete loss of heat sink, including loss of main feedwater. This analysis shows the overpressure protection that is afforded by the pressurizer and steam generator safety
valves.15.2.3.3 Conclusions Results of the analyses show that the plant design is such that a turbine trip without a direct or immediate reactor trip presents no hazard to the integrity
of the RCS or the main steam system. Pressure-relieving devices incorporated
in the two systems are adequate to limit the maximum pressures to within the
design limits. The analyses show that the DNBR will not decrease below the safety analysis limit at any time during the transient. Thus, the DNB design basis, as described in Section 4.4, is met. 15.2-9 Rev. 10 WOLF CREEK 15.2.4 INADVERTENT CLOSURE OF MAIN STEAM ISOLATION VALVES Inadvertent closure of the main steam isolation valves would result in a turbine trip with no credit taken for the turbine bypass system. Turbine trips are discussed in Section 15.2.3. 15.2.5 LOSS OF CONDENSER VACUUM AND OTHER EVENTS RESULTING IN TURBINE TRIP Loss of condenser vacuum is one of the events that can cause a turbine trip. Turbine trip initiating events are described in Section 15.2.3. A loss of
condenser vacuum would preclude the use of steam dump to the condenser; however, since steam dump is assumed to be unavailable in the turbine trip analysis, no additional adverse effects would result if the turbine trip were caused by loss of condenser vacuum. Therefore, the analysis results and
conclusions contained in Section 15.2.3 apply to the loss of the condenser
vacuum. In addition, analyses for the other possible causes of a turbine trip, as listed in Section 15.2.3.1, are covered by Section 15.2.3. Possible
overfrequency effects due to a turbine overspeed condition are discussed in
Section 15.2.2.1, and are not a concern for this type of event. 15.2.6 LOSS OF NON-EMERGENCY AC POWER TO THE STATION AUXILIARIES (BLACKOUT) 15.2.6.1 Identification of Causes and Accident Description A complete loss of nonemergency ac power may result in the loss of all power to the plant auxiliaries, i.e., the reactor coolant pumps, condensate pumps, etc.
The loss of power may be caused by a complete loss of the offsite grid
accompanied by a turbine generator trip at the station, or by a loss of the onsite ac distribution system. The DNB transient is more severe than the turbine trip event analyzed in Section 15.2.3 because, for this case, the decrease in heat removal by the secondary system is accompanied by a flow coastdown which further reduces the capacity of the primary coolant to remove heat from the core. The reactor will
trip: 1) due to turbine trip, 2) upon reaching one of the trip setpoints in the primary and secondary systems as a result of the flow coastdown and
decrease in secondary heat removal, or 3) due to the loss of power to the
control rod drive mechanisms as a result of the loss of power to the plant. Following a loss of ac power with turbine and reactor trips, the sequence described below will occur: 15.2-10 Rev. 13 WOLF CREEK
- a. Plant vital instruments are supplied from emergency dc power sources. b. As the steam system pressure rises following the trip, the steam generator atmospheric relief valves are automatically opened to the atmosphere. The condenser is assumed to be unavailable for turbine bypass. If the steam flow path through the atmospheric relief valves is not available, the steam generator safety valves may lift to dissipate the sensible heat of the fuel and coolant plus the residual decay heat produced in the reactor.
- c. As the no-load temperature is approached, the steam
generator atmospheric relief valves (or safety valves, if the atmospheric relief relief valves are not available) are used to dissipate the residual decay heat
and to maintain the plant at the hot shutdown condition.
- d. The standby diesel generators, started on loss of voltage on the plant emergency busses, begin to supply
plant vital loads. The auxiliary feedwater system is started automatically, as follows:
- a. Two motor-driven auxiliary feedwater pumps are started on any of the following:
- 1. Low-low level in any steam generator
- 2. Any safety injection signal
- 3. Loss of offsite power
- 4. Manual actuation
- b. The turbine-driven auxiliary feedwater pump is started on any of the following:
- 1. Low-low level in any two steam generators
- 2. Loss of offsite power
- 3. Manual actuation 15.2-11 Rev. 12 WOLF CREEK The motor-driven auxiliary feedwater pumps are supplied power by the diesels, and the turbine-driven pump utilizes steam from the secondary system. The
turbine exhausts the secondary steam to the atmosphere. The auxiliary feedwater pumps take suction from the condensate storage tank (or the essential service water system, if the condensate storage tank is unavailable) for
delivery to the steam generators. Upon the loss of power to the reactor coolant pumps, coolant flow necessary for core cooling and the removal of residual heat is maintained by natural
circulation in the reactor coolant loops. A loss of nonemergency ac power to the station auxiliaries is classified as an ANS Condition II event, fault of moderate frequency. This event is more limiting than the turbine-trip-initiated decrease in secondary heat removal
without loss of ac power, which was analyzed in Section 15.2.3. However, a
loss of ac power to the station auxiliaries, as postulated above, could also
result in a loss of normal feedwater if the condensate pumps lose their power
supply.Following the reactor coolant pump coastdown caused by the loss of ac power, the natural circulation capability of the RCS will remove residual and decay
heat from the core, aided by auxiliary feedwater in the secondary system. The
DNB transient for this event is bounded by the complete loss of flow event.
Thus the analysis is presented here to show that the natural circulation flow in the RCS following a loss of ac power event is sufficient to remove residual heat from the core. Major plant systems and equipment available for mitigation of transient and accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6.
The actual parameters assumed and results are given in the respective section/subsection. Table 15.0-6 incorporates events shown in the sequence diagram, Figure 15.0-12. 15.2.6.2 Analysis of Effects and Consequences Method of Analysis A detailed analysis of the loss of non-emergency AC transient has been performed using the RETRAN-3D computer code operating in the RETRAN-02 mode (Ref 5). RETRAN-3D operating in the RETRAN-02 mode has been found acceptable by the NRC for use as a licensing basis safety analysis code (Ref 6). RETRAN-02 is a thermal-hydraulic systems analysis code employing a one- dimensional, homogeneous equilibrium mixture thermal-hydraulic model for the RCS, a point kinetics model for the reactor core, special component and auxiliary models (ex., pumps, temperature transport, non-equilibrium pressurizer) and control system models. The code computes pertinent plant transient information
including core power level, RCS pressure and temperature. The assumptions used in the analysis are as follows: a. The plant is initially operating at 102 percent of the rated core power. b. A conservative core residual heat generation based upon long-term operation at the initial power level preceding the trip. 15.2-12 Rev. 24 WOLF CREEK c. A heat transfer coefficient (see Ref. 2) in the steam generator associated with RCS natural circulation.
- d. The auxiliary feedwater system is actuated by the low-low steam generator water level signal, assumed to occur at 0% of narrow range
span. The analysis assumes a total of 700 gpm is evenly delivered to 4 steam generators. This is a conservative minimum value for the AFW
flow and bounds either a single failure of the turbine-driven AFW
pump or one motor-driven AFW pump (e.g., diesel generator failure).
A delay of 415 seconds is assumed, including 60 seconds for diesel
generator and pump start, before delivering relatively cold auxiliary
feedwater to the steam generators. The delay allows for filling the
associated feedwater piping with no credit for the hotter main
feedwater being purged through the steam generators. The purge time
is based on the piping volume from the main feedwater and AFW check
valves (near the main feedwater and AFW junction) through the SG sparger ring. e. Reactor trip occurs when the steam generator level reaches 0.0% of narrow range span.
- f. The pressurizer spray valves and PORVS are assumed operable. This assumption maximizes the transient pressurizer water volume.
- g. The steam dump system and steam generator atmospheric relief valves are assumed to be unavailable. Secondary system steam relief is
assumed through the main steam safety valves (MSSVs) only.
Plant characteristics and initial conditions are further discussed in Section
15.0.3.
Results The transient response of the RCS following a loss of ac power is shown in
Figures 15.2-9 and 15.2-10. The calculated sequence of events for this event
is listed in Table 15.2-1.
The RETRAN code results demonstrate that the natural circulation flow available
is sufficient to provide adequate core decay heat removal following reactor
trip and reactor coolant pump coastdown. Table 15.2-4 lists the natural
circulation flow rates (in terms of percentage of full power) at no-load
conditions and each steam generator removing heat.
The analysis begins with a loss of normal feedwater resulting from a loss of
non-emergency AC power. This causes the steam generator level to fall, the RCS
temperature and pressurizer pressure to rise. When the reactor trips on low-low level, the reactor power drops toward decay heat levels, and the RCPs subsequently trip. Due to the reactor power reduction following reactor trip, the RCS temperature falls, as do the pressurizer pressure and level.
Following reactor trip, the focus of the analysis becomes the falling steam
generator inventory. While the inventory is high, there will be sufficient
heat transfer to remove the decay heat. However, the timely arrival of
auxiliary feedwater is sufficient to reverve the steam generator inventory
reduction at approximately 458 seconds.
Results of the analysis show that, for the loss of non-emergency AC to plant
auxiliaries, all safety criteria are met. Since the DNBR remains above the
design limit, the core is not adversely affected. Auxiliary feedwater capacity
is sufficient to prevent water relief through the pressurizer relief and safety valves; this assures that the RCS is not overpressurized. The calculated peak RCS pressure is approximately 2665 psia, which is less than 110% of the design
pressure (2750 psia).
15.2-13 Rev. 25 WOLF CREEK 15.2.6.3 Radiological Consequences 15.2.6.3.1 Method of Analysis 15.2.6.3.1.1 Physical Model
The dose calculation for loss of ac power is based on the sequence of events described in Table 15.2-1. It is assumed that heat removal from the nuclear steam supply system is achieved by venting the steam for 8 hours. The reactor coolant is assumed to be contaminated by radioactive fission products introduced through fuel cladding defects. The secondary system is
contaminated by the inleakage of reactor coolant through postulated steam
generator tube leaks. The radioactivity in the vented steam is dispersed in the atmosphere without any reduction due to plateout, fallout, filtering, etc. 15.2.6.3.1.2 Assumptions and Conditions The major assumptions and parameters assumed in the analysis are found in Tables 15.2-2 and 15.A-1. The assumptions used to determine the activity
released are as follows:
- a. The reactor coolant activity assumed is the Technical Specification limit of 1.0 Ci/gm I-131 dose equivalent.
- b. The initial steam generator activity assumed is the Technical Specification limit of 0.1 Ci/gm I-131 dose equivalent.
- c. A 1-gpm steam generator primary-to-secondary leakage is assumed for the duration of steam venting.
- d. For noble gases, the activity released is taken to be the activity introduced by reactor coolant inleakage
without holdup in the steam system.
- e. The iodine activity present in the primary-to-secondary leakage is assumed to be homogeneously mixed with the
iodine activity initially present in the steam generators. The iodine partition factor provided in
Table 15.2-2 is utilized to determine the iodine
activity released via steam venting from the steam generators.
- f. The atmospheric dispersion factors are given in Table 15A-2. 15.2-14 Rev. 13 WOLF CREEK 15.2.6.3.1.3 Mathematical Models Used in the Analysis Mathematical models used in the analysis are described in the following sections: a. The mathematical models used to analyze the activity released during the course of the accident are described in Appendix 15A.
- b. The atmospheric dispersion factors used in the analysis were calculated using the onsite meteorological
measurement programs described in Section 2.3.
- c. The thyroid inhalation and total-body immersion doses to a receptor at the exclusion area boundary or outer boundary of the low population zone were analyzed using
the models described in Appendix 15A. 15.2.6.3.1.4 Identification of Leakage Pathways and Resultant Leakage Activities Normal activity paths from the secondary system, such as the condenser air removal system and steam generator blowdown, cease during station blackout.
The steam is released to the atmosphere through the:
- a. Atmospheric relief valves
- b. Main steam safety valves Since all these paths are taken as direct to the atmosphere without any form of decontamination, they are all radiologically equivalent and need not be
distinguished. 15.2.6.3.2 Identification of Uncertainties in, and Conservative Aspects of, the Analysis The principal uncertainties in the dose calculation arise from the uncertainties in the accident circumstances, particularly the extent of steam
contamination, the weather at the time, and delay before preferred ac power is
restored. Each of these uncertainties is handled by making very conservative
or worst-case assumptions.
- a. Reactor coolant activities are based on the Technical Specification limit, which is significantly higher than
the activities associated with normal operating
conditions, based on 0.12-percent failed fuel. 15.2-15 Rev. 11 WOLF CREEK
- b. A 1-gpm steam generator primary-to-secondary leakage is assumed, which is significantly greater than that
anticipated during normal operation.
- c. The meteorological conditions which may be present at the site during the course of the accident are uncertain. However, it is highly unlikely that the assumed meteorological conditions would be present
during the course of the accident for any extended period of time. Therefore, the evaluated radiological
consequences, based on the meteorological conditions assumed, will be conservative. 15.2.6.3.3 Conclusions
15.2.6.3.3.1 Filter Loadings No filter serves to limit the release of radioactivity in this accident. There is no significant activity buildup on any filters as a consequence of loss of
ac power. 15.2.6.3.3.2 Doses to Receptor at Exclusion Area Boundary and Low Population Zone Outer Boundary The maximum doses to an individual who spends the first 2 hours after loss of ac power at the exclusion area boundary, and the maximum doses for a long-term exposure (8 hours or longer) at the outer boundary of the low-population zone, are given in Table 15.2-3. These doses are within a small fraction of the guideline values of 10 CFR 100. 15.2.6.4 Conclusions Results of the analysis show that, for the loss of non-emergency ac power to plant auxiliaries event, all safety criteria are met. Since the DNBR remains
above the design limit, the core is not adversely affected. Analysis of the natural circulation capability of the RCS demonstrates that sufficient long term heat removal capability exists following reactor coolant
pump coastdown to prevent fuel or clad damage. 15.2-16 Rev. 15 WOLF CREEK 15.2.7 LOSS OF NORMAL FEEDWATER FLOW 15.2.7.1 Identification of Causes and Accident Description A loss of normal feedwater (from pump failures, valve malfunctions, or loss of offsite ac power) results in a reduction in the capability of the secondary system to remove the heat generated in the reactor core. If an alternative supply of feedwater were not supplied to the plant, core residual heat following reactor trip would heat the primary system water to the point where water relief from the pressurizer would occur, resulting in a substantial loss of water from the RCS. The reactor trip on low-low water level in any steam generator provides the necessary protection against a loss of normal feedwater. The following occur upon loss of normal feedwater (assuming main feedwater pump failures or valve malfunctions):
- a. As the steam system pressure rises following the trip, the steam generator atmospheric relief valves are automatically opened to the atmosphere. The condenser is assumed to be unavailable for turbine bypass. If the steam flow path through the atmospheric relief valves is not available, the steam generator safety valves may lift to dissipate the sensible heat of the fuel and coolant plus the residual decay heat produced in the
reactor.
- b. As the no-load temperature is approached, the steam generator atmospheric relief valves (or safety valves, if the atmospheric relief valves are not available) are used to dissipate the residual decay heat and to maintain the plant at the hot shutdown condition.
A loss of normal feedwater is classified as an ANS Condition II event, fault of moderate frequency. See Section 15.0.1 for a discussion of Condition II
events.The auxiliary feedwater system is started automatically, as discussed in Section 15.2.6.1. The turbine-driven auxiliary feedwater pump utilizes steam from the secondary system and exhausts to the atmosphere. The motor-driven
auxiliary feedwater pumps are supplied power by the diesel generators. The
auxiliary feedwater pumps take suction directly from the condensate storage
tank (or essential service water system, if the condensate storage tank is
unavailable) for delivery to the steam generators. 15.2-17 Rev. 11 WOLF CREEK An analysis of the system transient is presented below to show that, following a loss of normal feedwater, the auxiliary feedwater system is capable of
removing the stored and residual heat, thus preventing either overpressurization of the RCS or loss of water from the reactor core, and returning the plant to a safe condition. 15.2.7.2 Analysis of Effects and Consequences Method of Analysis A detailed analysis of the loss of non-emergency AC transient has been performed using the RETRAN-3D computer code operating in the RETRAN-02 mode (Ref 5). RETRAN-3D operating in the RETRAN-02 mode has been found acceptable by the NRC for use as a licensing basis safety analysis code (Ref 6). RETRAN-02 is a thermal-hydraulic systems analysis code employing a one-dimensional, homogeneous equilibrium mixture thermal-hydraulic model for the RCS, a point
kinetics model for the reactor core, special component and auxiliary models (ex., pumps, temperature transport, non-equilibrium pressurizer) and control
system models. The code computes pertinent plant transient information
including core power level, RCS pressure and temperature. The assumptions used in the analysis are as follows:
- a. The plant is initially operating at 102 percent of the engineered safety features design rating.
- b. A conservative core residual heat generation, based upon long-term operation at the initial power level preceding
the trip.
- c. A heat transfer coefficient (see Ref. 2) in the steam generator associated with RCS natural circulation.
- d. Reactor trip occurs on steam generator low-low level at 0.0% of narrow range span.
- e. The auxiliary feedwater system is actuated by the low-low steam generator water level signal, assumed to occur at 0% of narrow range span. The analysis assumes a total of 700 gpm is evenly delivered to 4 steam generators. This is a conservative minimum value for the AFW flow and bounds either a single failure of the turbine-driven AFW
pump or one motor-driven AFW pump (e.g., diesel generator failure).
A delay of 415 seconds is assumed, including 60 seconds for diesel generator and pump start, before delivering relatively cold auxiliary feedwater to the steam generators. The delay allows for filling the
associated feedwater piping with no credit for the hotter main
feedwater being purged through the steam generators. The purge time is based on the piping volume from the main feedwater and AFW check valves (near the main feedwater and AFW junction) through the SG sparger ring.
- f. The auxiliary feedwater system is actuated by the low-low steam generator water level signal.
- g. Secondary system steam relief is achieved through the steam generator safety valves.
- h. The pressurizer sprays and PORVS are assumed operable.
This maximizes the peak transient pressurizer water
volume. 15.2-18 Rev. 24 WOLF CREEK The loss of normal feedwater analysis is performed to demonstrate the adequacy of the reactor protection and engineered safeguards systems (e.g., the
auxiliary feedwater system) in removing long-term decay heat and preventing excessive heatup of the RCS with possible resultant RCS overpressurization or loss of RCS water. As such, the assumptions used in this analysis are designed to minimize the energy removal capability of the system and to maximize the possibility of water relief from the coolant system by maximizing the coolant system
expansion, as noted in the assumptions listed above. For the loss of normal feedwater transient, the reactor coolant volumetric flow remains at its normal value, and the reactor trips via the low-low steam generator level trip. The reactor coolant pumps may be manually tripped at
some later time to reduce heat addition to the RCS. An additional assumption made for the loss of normal feedwater evaluation is that only the pressurizer safety valves are assumed to function normally.
Operation of the valves, if required, maintains peak RCS pressure below 110% of
design pressure throughout the transient. Plant characteristics and initial conditions are further discussed in Section 15.0.3.Major plant systems and equipment available for mitigation of transient and accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6. The actual parameters assumed and results are given in the respective section/subsection. Table 15.0-6 incorporates events shown in the sequence diagram, Figure 15.0-13. Normal reactor control systems are not required to function. The reactor protection system is required to function following a loss of normal feedwater, as analyzed here. The auxiliary feedwater system is
required to deliver a minimum auxiliary feedwater flow rate. No single active
failure will prevent operation of any system required to function. A
discussion of anticipated transients without scram (ATWS) considerations is
presented in Section 15.8. Results Figures 15.2-11 through 15.2-12 show the significant plant parameters following a loss of normal feedwater. The analysis begins with a loss of normal feedwater. This causes the steam generator level to fall, the RCS temperature to increase gradually and the pressurizer pressue and liquid level to rise. Due to the positive moderator temperature coefficent assumed, the reactor power also begins to rise. When the reactor trips on low-low steam generator level, the reactor power drops
toward decay heat levels. Due to the reactor power reduction, the RCS temperature falls, as do the pressurizer pressure and level. 15.2-19 Rev. 13 WOLF CREEK Following reactor trip, the focus of the transient analysis becomes the falling steam generator inventory. While the inventory is high, there will be
sufficient heat transfer to remove the core decay heat. However, the timely
arrival of auxiliary feedwater is sufficient to reverse the steam generator inventory reduction at approximately 458 seconds. The capacity of the
auxiliary feedwater pumps is such that the water level in the steam generators
is sufficient to dissipate core residual heat without water relief from the RCS
safety valves. Figure 15.2-12 shows that at no time is there water relief from
the pressurizer.
The results of the analysis show that, for the loss of normal feedwater event, all safety analysis criteria are met. Since the DNBR remains above the design
limit, the core is not adversely affected. The AFW capacity is also sufficient
to assure that the RCS does not overpressurize.
The calculated sequence of events for this accident is listed in Table 15.2-1.
As shown in Figures 15.2-11 and 15.2-12, the plant approaches a stabilized
condition following reactor trip and auxiliary feedwater initiation. Plant
procedures may be followed to further cool down the plant. 15.2.7.3 Conclusions Results of the analysis show that a loss of normal feedwater does not adversely
affect the core, the RCS, or the steam system, since the auxiliary feedwater
capacity is such that reactor coolant water is not relieved from the pressurizer relief or safety valves.
15.2.8 FEEDWATER SYSTEM PIPE BREAK
15.2.8.1 Identification of Causes and Accident Description A major feedwater line rupture is defined as a break in a feedwater line large
enough to prevent the addition of sufficient feedwater to the steam generators
to maintain shell side fluid inventory in the steam generators. If the break is postulated in a feedwater line between the check valve and the steam
generator, fluid from the steam generator may also be discharged through the
break. Further, a break in this location could preclude the subsequent
addition of auxiliary feedwater to the affected steam generator. (A break
upstream of the feedwater line check valve would affect the NSSS only as a loss
of feedwater. This case is covered by the evaluation in Sections 15.2.6 and
15.2.7.)
Depending upon the size of the break and the plant operating conditions at the
time of the break, the break could cause either an RCS cooldown (by excessive energy discharge through the break) or an RCS heatup. Potential RCS cooldown resulting from a secondary pipe rupture is evaluated in Section 15.1.5.
Therefore, only the RCS heatup effects are evaluated for a feedwater line
rupture.
A feedwater line rupture reduces the ability to remove heat generated by the
core from the RCS for the following reasons:
- a. Feedwater flow to the steam generators is reduced.
Since feedwater is subcooled, its loss may cause reactor
coolant temperatures to increase prior to reactor trip.
15.2-20 Rev. 25 WOLF CREEK
- b. Fluid in the steam generator may be discharged through the break, and would then not be available for decay
heat removal after trip.
- c. The break may be large enough to prevent the addition of any main feedwater after trip.
An auxiliary feedwater system functions to ensure the availability of adequate feedwater so that:
- a. No substantial overpressurization of the RCS occurs (less than 110 percent of design pressures); and
- b. Sufficient liquid in the RCS is maintained so that the core remains in place and geometrically intact with no
loss of core cooling capability. A major feedwater line rupture is classified as an ANS Condition IV event. See Section 15.0.1 for a discussion of Condition IV events. The severity of the feedwater line rupture transient depends on a number of system parameters, including break size, initial reactor power, and credit
taken for the functioning of various control and safety systems. Sensitivity
studies presented in Reference 3 illustrate many of the limiting assumptions
for the feedwater line rupture. In addition, the major assumptions pertinent to this analysis are defined below. The main feedwater control system is assumed to fail due to an adverse environment. The water levels in all steam generators are assumed to decrease
equally until the low-low steam generator level reactor trip setpoint is reached. After reactor trip, a double-ended rupture of the largest feedwater line is assumed. These assumptions conservatively bound the most limiting feedwater line rupture that can occur. Analyses have been performed at full
power, with and without loss of offsite power, and with no credit taken for the
pressurizer power-operated relief valves. For the case without offsite power
available, the power is assumed to be lost at the time of reactor trip. This
is more conservative than the case where power is lost at the initiation of the
event. These cases are analyzed below. The following provides the protection for a main feedwater line rupture:
- a. A reactor trip on any of the following conditions:
- 1. High pressurizer pressure
- 2. Overtemperature T 15.2-21 Rev. 0 WOLF CREEK
- 3. Low-low steam generator water level in any steam generator
- 4. Safety injection signals from any of the following:
- 1) two-out-of-three low steam line pressure in any one loop or 2) two-out-of-three high containment
pressure (hi-1) Refer to Chapter 7.0 for a description of the actuation system.
- b. The auxiliary feedwater system provides an assured source of feedwater to the steam generators for decay heat removal. Refer to Section 10.4.9 for a description of the auxiliary feedwater system.
Major plant systems and equipment available for mitigation of transient and accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6.
The actual parameters assumed and results are given in the respective
section/subsection. Table 15.0-6 incorporates events shown in the sequence
diagram, Figure 15.0-14. 15.2.8.2 Analysis of Effects and Consequences Method of Analysis A detailed analysis of the feedwater line break event has been performed using the RETRAN-3D computer code operating in the RETRAN-02 mode (Ref 5). RETRAN-3D
operating in the RETRAN-02 mode has been found acceptable by the NRC for use as
a licensing basis safety analysis code (Ref 6). RETRAN-02 is a thermal-hydraulic systems analysis code employing a one-dimensional, homogeneous equilibrium mixture thermal-hydraulic model for the RCS, a point kinetics model
for the reactor core, special component and auxiliary models (ex., pumps, temperature transport, non-equilibrium pressurizer) and control system models. The code computes pertinent plant transient information including core power level, RCS pressure and temperature. Major assumptions used in the analysis are as follows:
- a. The initial Plant Power is assumed to be 102% of rated core power. Plant characteristics and initial conditions are further discussed in Section 15.0.
- b. No credit is taken for the pressurizer power-operated relief valves or pressurizer spray.
- c. Initial pressurizer level is at the nominal programmed value plus 5 percent (error); initial steam generator water level in all SGs is at the nominal value, plus 5.7%
of the narrow range span. Since this transient is a heatup event which leads to a pressurization of the RCS, a higher SG water level tends to prolong the initiating event sequence prior to reactor trip on low-low SG level, increasing the initial RCS heatup and the associated power increase (the BOL moderator temperature coefficient is positive). 15.2-22 Rev. 24 WOLF CREEK
- d. No credit is taken for the high pressurizer pressure reactor trip. e. Main feedwater is assumed to be lost to all SGs at event initiation due to a malfunction in the feedwater control system under an adverse environment. The feedwater line break, and subsequent reverse blowdown of the faulted SG, is conservatively assumed to occur when the SG inventory reaches
0% narrow range span (i.e., reactor trip on low-low SG water level of 23.5%, minus environmental allowance and uncertainties).
The combination of errors described above yields the most severe feedwater line break transient, with control and protection interaction considered.
- f. The worst possible break area is assumed. This maximizes the blowdown discharge rate following the time of
trip, which maximizes the resultant heatup of the
reactor coolant.
- g. A bounding feedwater line break discharge quality is assumed. h. Failure of one protection train is taken as the worst single failure so that the second motor driven AFW pump is assumed inoperable. The total AFW flow delivered to the three intact SGs is assumed to be 563 gpm. This is a conservative minimum value for the AFW flow and bounds either a single failure of the turbine-driven AFW pump or one motor-driven AFW pump. Credit is taken for the discharge flow control device installed on the AFW header common to both the motor driven and turbine driven AFW pumps. Due to this discharge flow control device, the intact SG receiving AFW from both the motor driven and turbine driven AFW pumps is assumed to receive no more than 250 gpm. The remaining two intact SGs which receive AFW from only the turbine driven AFW pump are assumed to receive approximately 157 gpm each. i. The auxiliary feedwater system is actuated by the low- low steam generator water level signal. A 60-second delay was assumed following the low-low level signal to allow time for startup of the standby diesel generators and the auxiliary feedwater pumps. An additional 325 seconds was assumed before the feedwater lines were purged and the relatively cold (120 F) auxiliary feedwater entered the unaffected steam generators. The purge time is based on the piping volume from the main feedwater and AFW check valves (near the main feedwater and AFW junction) through the SG sparger ring.
- j. No credit is taken for heat energy deposited in RCS
metal during the RCS heatup.
- k. No credit is taken for charging or letdown.
- l. Steam generator heat transfer area is assumed to decrease as the shell side liquid inventory decreases.
- m. Conservative core residual heat generation is assumed based upon long-term operation at the initial power
level preceding the trip.
- n. No credit is taken for the following potential protection logic signals to mitigate the consequences of the accident: 15.2-23 Rev. 24 WOLF CREEK
- 1. High pressurizer pressure
- 2. Overtemperature T 3. High pressurizer level
- 4. High containment pressure Receipt of a low-low steam generator water level signal in at least one steam generator starts the motor-driven auxiliary feedwater pumps, which in turn
initiate auxiliary feedwater flow to the steam generators. The turbine-driven
auxiliary feedwater pump is initiated if the low-low steam generator water level signal is reached in at least two steam generators. Similarly, receipt
of a low steam line pressure signal in at least one steam line initiates a
steam line isolation signal which closes all main steam line isolation valves. Emergency operating procedures following a feedwater system pipe rupture require the following actions to be taken by the reactor operator:
- a. Isolate feedwater flow spilling from the ruptured feed-water line and align the system so that the level in the intact steam generators is recovered.
- b. High head safety injection should be terminated in accordance with the emergency operating procedures.
Subsequent to terminating high head safety injection, plant operating procedures are followed in cooling the plant to a safe shutdown condition. Plant characteristics and initial conditions are further discussed in Section 15.0.3.No reactor control systems are assumed to function. The reactor protection system is required to function following a feedwater line rupture as analyzed
here. No single active failure will prevent operation of this system. The engineered safety systems assumed to function are the auxiliary feedwater system and the safety injection system. For the auxiliary feedwater system, the worst case configuration has been used, i.e., only three intact steam generators receive auxiliary feedwater following the break. A discharge flow control device, located on the auxiliary feedwater line to each steam generator, is assumed to regulate the flow from the motor-driven auxiliary feedwater pump to the affected steam generator. This ensures that 15.2-24 Rev. 7 WOLF CREEK a minimum flow of 250 gpm, from both the motor-driven and turbine-driven auxiliary feedwater pumps, is delivered to the intact steam generator feed by
the same motor-driven auxiliary feedwater pump that is feeding the affected steam generator. The second motor-driven auxiliary feedwater pump has been assumed to fail. The turbine-driven auxiliary feedwater pump delivers 470 gpm
equally split to the three intact steam generators. This assumption is conservative because it maximizes the purge time in the feedwater lines before auxiliary feedwater enters the unaffected steam generators. Thus, a total
flow of 563 gpm is delivered to the intact steam generators. Two separate cases are analyzed, i.e., with and without offsite power. Where offsite power is available, the reactor coolant pumps continue to operate after the reactor trip. In the case where offsite power is not available, the reactor coolant pumps coast down upon loss of offsite power which is assumed to occur at the reactor trip. For the case without offsite power, there is a flow coastdown until flow in the loops reaches the natural circulation value. The natural circulation capability of the RCS has been shown (in Section 15.2.6) to be sufficient to remove core decay heat following reactor trip, for the loss of ac power transient. Pump coastdown characteristics are demonstrated in Sections 15.3.1 and 15.3.2 for single and multiple reactor coolant pump trips, respectively. A detailed description and analysis of the safety injection system is provided in Section 6.3. The auxiliary feedwater system is described in Section 10.4.9.Results Calculated plant parameters following a major feedwater line rupture are shown in Figures 15.2-13 through 15.2-22. Results for the case with offsite power
available are presented in Figures 15.2-13 through 15.2-17. Results for the
case where offsite power is lost are presented in Figures 15.2-18 through 15.2-
- 22. The calculated sequence of events for both cases analyzed are listed in
Table 15.2-1. The system response following the feedwater line rupture is similar for both cases analyzed. In both cases, the primary and secondary pressures increase prior to reactor trip. After reactor trip occurs on low-low SG water level, the pressure decreases sharply, due to the cooldown caused by the break, until steam line isolation occurs. The pressure in the faulted SG continues to decrease, while the pressure in the intact SGs and primary side begins to increase (cooldown ends, heat-up begins) until the safety valve settings are reached. Results presented in Figures 15.2-14 and 15.2-15 (with offsite power available) and Figures 15.2-19 and 15.2-20 (without offsite power) show that pressures in the RCS and main steam system remain below 110 percent of the
respective design pressures. The primary temperatures increase prior to reactor trip and decrease sharply during cooldown after reactor trip. Once the heat-up begins, the primary temperature increases until the heat removal capability of the intact SGs, with the inventory maintained by the AFW System, equals the decay heat generated in the core plus pump heat (turnaround time). The peak primary temperature remains below the saturation temperature although the margin to boiling is decreased. Thus, there is no bulk boiling in the RCS. In addition, the pressurizer does not fill due to thermal expansion nor does the pressurizer empty. Therefore, the reactor remains covered with water throughout the transient. 15.2-25 Rev. 22 WOLF CREEK Figures 15.2-13 and 15.2-18 show that following reactor trip the plant remains subcritical. The major difference between the two cases analyzed can be seen in the plots of hot and cold leg temperatures, Figure 15.2-16 (with offsite power available) and Figure 15.2-21 (without offsite power). It is apparent that for the initial transient (~150 seconds), the case without offsite power results in higher temperatures in the hot leg. For longer times, however, the case with offsite power results in a more severe rise in temperature until the auxiliary feedwater system is realigned. AFWS realignment is not assumed, however, in
these cases. The pressurizer fills more rapidly for the case with power due to the increased coolant expansion resulting from the pump heat addition. As
previously stated, the core remains covered with water for both cases. 15.2.8.3 Conclusions
Results of the analyses show that for the postulated feedwater line rupture, the assumed auxiliary feedwater system capacity is adequate to remove decay
heat, to prevent overpressurizing the RCS, and to prevent uncovering the reactor core. Radioactivity doses from the postulated feedwater lines rupture
are less than those previously presented for the postulated steam line break.
All applicable acceptance criteria are therefore met. 15.
2.9 REFERENCES
- 1. Cooper, L., Miselis, V. and Starek, R. M., "Overpressure Protection for Westinghouse Pressurized Water Reactors,"
WCAP-7769, Revision 1, June, 1972 (also letter NS-CE-622, dated April 16, 1975, C. Eicheldinger (Westinghouse) to D.B. Vassallo (NRC), additional information on WCAP-7769, Revision 1). 2. Burnett, T. W. T., et al., "LOFTRAN Code Description," WCAP-7907A, April 1984.
- 3. Lang, G. E. and Cunningham, J. P., "Report on the Consequences of a Postulated Main Feedline Rupture," WCAP-9230 (Proprietary) and WCAP-9231 (Non-Proprietary), January 1978. 5. Paulsen, M. P., et. al., RETRAN-3D: A Program for Transient Thermal-Hydraulic Analysis of Complex Fluid Flow Systems, EPRI NP-7450(A). July 2001. 6. Safety Evaluation Report on EPRI Topical Report NP-7450(P), Revision 4, RETRAN-3D - A Program for Transient Thermal-hydraulic Analysis for Complex Fluid Flow Systems (TAC No MA4311). Dated 1/25/2001. 7. WCAP-11397-P-A, "Revised Thermal Design Procedure," A. J. Fiedland, et al., April 1989. 15.2-26 Rev. 22 WOLF CREEK TABLE 15.2-1 TIME SEQUENCE OF EVENTS FOR INCIDENTS WHICH RESULT IN A DECREASE IN HEAT REMOVAL BY THE SECONDARY SYSTEM Time Accident Event (sec)Turbine Trip 1. Overpressure evaluation without pressurizer control (minimum
feedback)Turbine trip; Loss of main feedwater
flow 0.025 Initiation of steam release from pressurizer relief valve NONE High pressurizer pressure reactor trip setpoint reached 5.45 Initiation of steam release from steam generator safety valves 5.55 Rods begin to drop 7.45 Initiation of steam release from pressurizer safety valve 7.65 Peak pressurizer pressure occurs 8.00
- 2. Overpressure evaluation without pressurizer
control (maximum feedback)Turbine trip; Loss of main feedwater flow 0.025 Initiation of steam release from pressurizer relief valve NONE High pressurizer pressure reactor trip setpoint reached 5.45 Initiation of steam release from steam generator safety valves 5.55 Rods begin to drop 7.45 Initiation of steam release from pressurizer safety valve 7.60 Peak pressurizer pressure occurs 7.90 Rev. 10 WOLF CREEK TABLE 15.2-1 (S heet 2) Time Accident Event (sec)Turbine Trip 3. DNB evaluation with pressurizer control (minimum feedback) Turbine trip; Loss of main feedwater flow 0.025 Initiation of steam release from pressurizer relief valve 3.85 Initiation of steam release from steam generator safety valves 7.74 High pressurizer pressure reactor trip setpoint reached 9.04 Rods begin to drop 11.04 Initiation of steam release from pressurizer safety valve 11.90 Peak system pressure occurs 12.05
- 4. DNB evaluation with pressurizer control (maximum feedback)
Turbine trip; Loss of main feedwater flow 0.025 Initiation of steam release from pressurizer relief valve 3.85 Initiation of steam release from steam generator safety valves 7.74 High pressurizer pressure reactor trip setpoint reached 9.50 Rods begin to drop 11.50 Peak system pressure occurs 13.20 Rev. 10 WOLF CREEK TABLE 15.2-1 (S heet 3) Time Accident Event (sec)Loss of nonemergency ac power to the station auxiliaries Main feedwater flow stops 0.1 Low-low steam generator water level trip 40.8 Rods begin to drop 42.9 Reactor coolant pumps begin to coast down 44.9 1 st steam generator safety valve open 74.1 S team generator inventory reduction reverses after AFW flow from two motor-driven auxiliary feedwater pumps or one motor-driven auxiliary feedwater pump and the turbine driven pump is received 457.9 Loss of normal feedwater flow Main feedwater flow stops 0.1 Low-low steam generator water level trip 40.8 Rods begin to drop 42.9 1 st steam generator safety valve open 73.1 S team generator inventory reduction reverses after AFW flow from two motor-driven auxiliary feedwater pumps or one motor-driven auxiliary feedwater pump and the turbine driven pump is received 457.9 Rev. 24 WOLF CREEK TABLE 15.2-1 (Sheet 4) Time Accident Event (sec)Feedwater system pipe break Actions/Events With offsite power available Steady State Operation 0.00 Feedwater Control System Failed 10.00 Pressurizer Safety Valve Opens 31.74 Low-Low SG Water Level Setpoint Reached 54.10 Reactor Trip on Low-Low SG Water Level and Feedwater Line Break Occurs 56.13 SG Safety Valve #1 Opens 56.29 SG Safety Valve #2 Opens 56.33 Pressurizer Safety Valve Closes 60.15 Steam Line Low Pressure Setpoint Reached in Faulted SG 86.00 SG Safety Valve #2 Closes 86.66 SG Safety Valve #1 Closes 88.25 All MSIVs Closed 103.00 Centrifugal Charging Pump Begins to Deliver Injection Flow on Low Pressurizer Pressure 138.85 SG Safety Valve #1 Opens 236.32 AFW is Delivered to Intact SGs 429.10 Pressurizer Safety Valve Opens 424.22 Pressurizer Safety Valve Closes 1788.11 Core Decay Heat Decreases to AFW Heat Removal Capacity 1770.00 Rev. 24 WOLF CREEK TABLE 15.2-1 (Sheet 5) Time Accident Event (sec)Feedwater system pipe break continue Actions/Events Without offsite power available Steady State Operation 0.00 Feedwater Control System Failed 10.00 Pressurizer Safety Valve Opens 31.74 Low-Low SG Water Level Setpoint Reached 54.10 Reactor Trip on Low-Low SG Water Level and Feedwater Line Break Occurs 56.13 SG Safety Valve #1 Opens 56.29 SG Safety Valve #2 Opens 56.31 Pressurizer Safety Valve Closes 60.85 Steam Line Low Pressure Setpoint Reached in Faulted SG 83.12 SG Safety Valve #2 Closes 83.85 SG Safety Valve #1 Closes 85.22 All MSIVs Closed 100.12 Centrifugal Charging Pump Begins to Deliver Injection Flow on Low Pressurizer Pressure 157.61 SG Safety Valve #1 Opens 236.30 AFW is Delivered to Intact SGs 439.10 Pressurizer Safety Valve Opens 427.46 Pressurizer Safety Valve Closes 926.80 Core Decay Heat Decreases to AFW Heat Removal Capacity 872.00 Rev. 24 WOLF CREEK TABLE 15.2-2 PARAMETERS USED IN EVALUATING RADIOLOGICAL CONSEQUENCES OF LOSS OF NONEMERGENCY AC POWERI.Source Dataa.Steam generator type leakage, gpm1b.Reactor coolant initial iodine activity 1.0µCi/gm of I-131 dose equivalentc.Secondary system initial iodine activity 0.1µCi/gm of I-131 dose
equivalentd.Reactor coolant initial noble gas activityBased on 1% failed fuel, see Table 11.1-5e.Iodine partition factor in the steam generator 0.01f.Each steam generator water mass, lb9.55E+4II.Atmospheric Dispersion FactorsSee Table 15A-2III.Activity Release Dataa.Total primary to secondary leakage 0-8 hr, lb4000b.Steam release from all steam generators 0-2hours, lb5.49E+52-8 hours, lb1.03E+6c.Activity released to the environmentIsotope0-2 hr (Ci)0-8 hr (Ci)I-1311.83E-15.31E-1I-1321.54E-12.55E-1I-1333.12E-18.42E-1I-1342.47E-22.87E-2I-1351.71E-13.95E-1Xe-131m1.546.13Xe-133m2.419.26Xe-1331.31E+25.15E+2Xe-135m5.13E-25.15E-2Xe-1354.141.34E+1Xe-1374.68E-34.68E-3Xe-1386.30E-26.31E-2Kr-83m1.76E-13.15E-1Kr-85m8.82E-12.35Kr-854.271.71E+1Kr-874.06E-16.04E-1Kr-881.533.40Kr-892.09E-32.09E-3 Rev. 13 WOLF CREEK TABLE 15.2-3 RADIOLOGICAL CONSEQUENCES OF LOSS OF NON-EMERGENCY AC POWER Wolf Creek Dose (rem) Exclusion area boundary (0-2 hr)Thyroid, rem1.92E-2Whole body, rem3.84E-4 Low-population zone, outer boundary (duration)Thyroid, rem7.24E-3Whole body, rem1.60E-4 Rev. 13 WOLF CREEK TABLE 15.2-4 NATURAL CIRCULATION FLOW Core Power (percent)RCS Natural Circulation Flow (percent)5.05.94.05.43.04.82.04.11.03.2 Rev. 7
jo.e -..... ..!!! ! 0.2 0 5 10 15 20 Time (sec} 2,800 ,...---------------------------, 2,600 , ' , ' I ' ' ' ' ' ; 2,400 MaximumRCS I 2.200 2,0000 5 10 inne (sec) 15 WOLF CREEK 20 Rev. 10 UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-1 NUCLEAR POWER AND PRESSURE FOR TURBINE TRIP EVENT WITH MINIMUM REACTIVITY FEEDBACK OVERPRESSURE EVALUATION 2 1,350 ]. 1,300 :I :g 1,250 :3" 11,200 i II) £ 1,150 1,100 ,__ ______ ..___ ____ ...;..._ ____ ....:..,_ ____ _, 0 5 10 15 20 620 --560 Time (sec) __.---*-..... ... -----... ..........__ .. _ *-----_ ...... , , , 5 , ... .. --------------------10 riTile (sec) 15 WOLF CREEK 20 Rev. 10 UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-2 PRESSURIZER LIQUID VOLUME AND RCS TEMPERATURE FOR TURBINE TRIP EVENT WITH MINIMUM REACTIVITY . FEEDBACK OVERPRESSURE EVALUATION L 1.2 1 ... 0.6 ... Ill IU u :2 0.4 0.2. 0 0 5 10 15 20 Time (sec) 2.800 ' \ ' ' 2,600 ...... ID Vi Pressurizer .&; 2,400 MaximumRCS II) ! c. 2.200 0 5 10 15 20 Time (sec) Rev. 10 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-3 NUCLEAR POWER AND PRESSURE FOR TURBINE TRIP EVENT WlTH MAXIMUM REACTIVITY FEEDBACK OVERPRESSURE EVALUATION .....
- 1.350 .[ 1,300 2 1.250 g j1,200 ! Q.. 1,150 1,100 0 620 560 ----5 10 Time (sec) 15 20 -----------
...... __ Avg. Hot Leg Avg. Colli Leg Veaael AWII'IIgll 0 6 10 Tune (sec) 15 WOLF CREEK 20 Rev. 1.0 UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-4 PRESSURIZER LIQUID VOLUME AND RCS 'l'EMPERATURE FOR TURBINE TRIP EVENT WITH MAXIMUM REACTIVITY FEEDBACK OVERPRESSURE EVALUATION "' ........................ .. I a. 0.6 i u 0.4 0.2 5 10 Ttme (sec) 15 20 2,700 2,600 j'2,500 .s 2.400 I'D I'D £ 2,300 2,200 2,100 , ---, ' , , , . . MaximumRCS 0 5 10 15 20 Time(sec) Rev. 10 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-5 NUCLEAR POWER AND PRESSURE FOR TURBINE TRIP EVENT WITH MINIMUM REACTIVITY FEEDBACK DNB EVALUATION 1,700----------------------, e 1.600 1.500 :J 1.400 ! 1,300 I Q: 1.200 1,100 OL------6'-------..:10 ____ __.,:15 __ ........__---120 Time (sec) 640 620 i *---- l i580 _,. _ ... -5 ... " --------------- .. ,.-10 Tlme (sec:) 15 20 Rev. 10 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-6 PRESSURIZER LIQUID VOLUME AND RCS TEMPERATURE FOR TURBINE TRil? EVENT WITH MINIMUM REACTIVITY FEEDBACK DNB EVALUATION G 1.2 I --g 0.8 L. CL. 0.6 ... ca Cll ll £0.4 0.2 0 0 5 10 15 20 Time (sec) 2,700 2.600 . --* ' . 2,500 ...... . !! .s 2,400 !! :J i 2,300 CL. 2.200 2,100 2,000 0 5 10 16 20 lime (sec) Rev. 10 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-7 NUCLEAR POWER AND PRESSURE FOR TURBINE TRIP EVENT WITH MAXIMUM REACTIVITY FEEDBACK DNB EVALUATION 0 .. :<('** ... 1,700...---------------------, i2"1,600 :i 1,500 1,400 !Z ... .§ 1,300 I 1,100 0 5 10 15 Tme(sec) 640 "=' 620 i :g. 2 eoo i l E58Q ... --_ .. -__ ,, _________ .,. ___ _ .. -...... ,-,. Tane(sec) Rev. 10 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-8 PRESSURIZER LIQUID VOLUME AND RCS TEMPERATURE FOR TURBINE TRIP EVENT WITH MAXIMUM REACTIVITY FEEDBACK DNB EVALUATION Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-9 NUCLEAR POWER, REACT OR COOLANT FLOW RATE AND STEAM GENERATOR PRESSURE TRANSIENTS FOR LOSS OF AC POWER 0 1000 2000 3000 4000 50000100200300400500Time (sec) Power (MWt) 0.00.20.40.60.8 1.0 1.20100200300400500 Time (sec) Core Flow (fraction of nominal) 700 800 900 1000 1100 1200 13000100200300400500Time (sec)SG Pressure (psia) Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-10 REACTOR COOLANT TEMPERATURE, MAXIMUM RCS PRESSURE AND PRESSURIZER LIQUID LEVEL FOR LOSS OF AC POWER 560 570 580 590 6000100200300400500 Time (sec) RCS Average Temperature (degrees F) 2000 2100 2200 2300 2400 2500 26000100200300400500 Time (sec)RCS Pressure (psia) 20 25 30 35 40 450100200300400500 Time (sec) Pressurizer Level (ft) Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-11 NUCLEAR POWER AND STEAM GENERATOR PRESSURE TRANSIENTS FOR LOSS OF NORMAL FEEDWATER 0100020003000400050000100200300400500Time (sec) Power (MWth) 700800 9001000 1100120013000100200300400500Time (sec)SG Pressure (psia) Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-12 CORE AVERAGE TEMPERATURE, MAXIMUM RCS PRESSURE AND PRESSURIZER LIQUID LEVEL TRANSIENTS FOR LOSS OF NORMAL FEEDWATER 560565570575 5805855900100200300400500Time (sec)RCS Average Temperature (degrees F) 2200 2300 2400 2500 26000100200300400500Time (sec) RCS Pressure (psia) 20 25 30 35 40 450100200300400500Time (sec)Pressurizer Level (ft) 0.00.2 0.40.60.81.01.21.4110100100010000Elapsed Time (seconds)Power (Fraction of N ominal) Normalized Core Power 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4110100100010000Elapsed Time (seconds) Core Heat Flux (Fraction of N ominal)Core Heat Flux-4000-3000 -2000-1000 01000110100100010000Elapsed Time (seconds)Total Core Reactivity (pcm) Total Reactivity Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-13 NUCLEAR POWER, CORE HEAT FLUX AND TOTAL CORE REACTIVITY FOR MAIN FEEDWATER LINE RUPTURE WITH OFFSITE POWER AVAILABLE Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-14 PRESSURIZER AND MAXIMUM SYSTEM PRESSURE AND PR ESSURIZER WATER VOLUME FOR MAIN FEEDWATER LINE RUPTURE WITH OFFSITE POWER AVAILABLE 1500170019002100230025002700110100100010000Elapsed Time (seconds)Pressure (psia)Pressurizer PressureMaximum RCS Pressure 0200400600800100012001400160018002000110100100010000Elapsed Time (seconds)Volume (cu. ft.) Pressurizer Liquid Volume 0.880.900.920.940.960.981.00110100100010000Elapsed Time (seconds)Mass Flow Rate (Fraction of Nominal) Core Flow-0.6-0.4-0.20.00.20.4110100100010000Elapsed Time (seconds)Mass Flow Rate (Fraction of Nominal) Faulted Loop Feed/Break Flow Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-15 REACTOR COOLANT FLOW AND FEEDWATER LINE BREAK FLOW FOR MAIN FEEDWATER LINE RUPTURE WITH OFFSITE POWER AVAILABLE 350400450500550600650700110100100010000Elpased Time (seconds)Temperature (deg. F)Faulted Loop Hot Leg TempFaulted LoopCold Leg TempFaulted Loop Hot Leg T-sat 540 560 580 600 620 640 660 680 700110100100010000Elapsed Time (seconds)Temperature (deg. F)Intact Loop Hot Leg TempIntact Loop Cold Leg TempIntact Loop Hot Leg T-sat Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-16 FAULTED LOOP AND INTACT LOOP REACTOR COOLANT TEMPERATURE FOR MAIN FEEDWATER LINE RUPTURE WITH OFFSITE POWER AVAILABLE 0200400600800100012001400110100100010000Elapsed Time (seconds)Pressure (psia)Intact Steam GeneratorPressureFaulted Steam Generator Pressure-2.0E+090.0E+002.0E+094.0E+096.0E+098.0E+091.0E+101.2E+101.4E+101.6E+10110100100010000Elapsed Time (seconds)Power (Btu/hr)Total Thermal PowerTotal Steam GeneratorHeat Transer Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-17 STEAM GENERATOR PRESSURE AND ENERGY FOR MAIN FEEDWATER LINE RUPTURE WITH OFFSITE POWER AVAILABLE 0.00.20.40.60.81.01.21.4110100100010000Elapsed Time (seconds) P ower (Fraction of N ominal)Normalized Core Power-4000-3000-2000-1000 01000110100100010000Elapsed Time (seconds)Total Core Reactivity (pcm )Total Reactivity-0.6-0.4-0.2 0.0 0.2 0.4110100100010000Elapsed Time (seconds) Mass Flow Rate (Fraction of N ominal) Faulted Loop Feed/Break Flow Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-18 NUCLEAR POWER, CORE HEAT FLUX AND TOTAL CORE REACTIVITY FOR MAIN FEEDWATER LINE RUPTURE WITHOUT OFFSITE POWER 1500170019002100230025002700110100100010000Elapsed Time (seconds)Pressure (psia)Pressurizer PressureMaximum RCS Pressure 0 200 400 600 8001000 1200 1400160018002000110100100010000Elapsed Time (seconds)Volume (cu. ft.) Pressurizer Liquid Volume Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-19 PRESSURIZER AND MAXIMUM SYSTEM PRESSURE AND PR ESSURIZER WATER VOLUME FOR MAIN FEEDWATER LINE RUPTURE WITHOUT OFFSITE POWER 0.00 0.20 0.40 0.60 0.80 1.00110100100010000Elapsed Time (seconds)Mass Flow Rate (Fraction of Nominal) Core Flow-0.6-0.4 -0.2 0.0 0.2 0.4110100100010000Elapsed Time (seconds)Mass Flow Rate (Fraction of Nominal) Faulted Loop Feed/Break Flow Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-20 REACTOR COOLANT FLOW AND FEEDWATER LINE BREAK FLOW FOR MAIN FEEDWATER LINE RUPTURE WITHOUT OFFSITE POWER 540560 580 600 620640660 680700110100100010000Elapsed Time (seconds)Temperature (deg. F)Intact Loop Hot Leg TempIntact Loop Cold Leg TempIntact Loop Hot Leg T-sat350400 450500550 600 650 700110100100010000Elpased Time (seconds)Temperature (deg. F)Faulted Loop Hot Leg TempFaulted LoopCold Leg TempFaulted Loop Hot Leg T-sat Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-21 FAULTED LOOP AND INTACT LOOP REACTOR COOLANT TEMPERATURE FOR MAIN FEEDWATER LINE RUPTURE WITHOUT OFFSITE POWER 0200400600800100012001400110100100010000Elapsed Time (seconds)Pressure (psia)Intact Steam GeneratorPressureFaulted Steam Generator Pressure-2.0E+090.0E+002.0E+094.0E+09 6.0E+098.0E+091.0E+101.2E+101.4E+101.6E+10110100100010000Elapsed Time (seconds)Power (Btu/hr)Total Thermal PowerTotal Steam GeneratorHeat Transer Rev. 24 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.2-22 STEAM GENERATOR PRESSURE AND ENERGY FOR MAIN FEEDWATER LINE RUPTURE WITHOUT OFFSITE POWER WOLF CREEK 15.3 DECREASE IN REACTOR COOLANT SYSTEM FLOW RATE
A number of faults which could result in a decrease in the reactor coolant
system (RCS) flow rate are postulated. These events are discussed in this
section. Detailed analyses are presented for the most limiting of the following flow decrease events:
- a. Partial loss of forced reactor coolant flow
- b. Complete loss of forced reactor coolant flow
- c. Reactor coolant pump shaft seizure (locked rotor)
- d. Reactor coolant pump shaft break
Item a above is considered to be an ANS Condition II event, item b an ANS
Condition III event, and items c and d ANS Condition IV events. Section 15.0.1
contains a discussion of ANS classifications. All of the accidents in this section have been analyzed. It has been
determined that the most severe radiological consequences will result from the
reactor coolant pump shaft seizure accident of Section 15.3.3. Therefore, doses are reported only for that limiting case.
15.3.1 PARTIAL LOSS OF FORCED REACTOR COOLANT FLOW
15.3.1.1 Identification of Causes and Accident Description A partial loss-of-coolant flow accident can result from a mechanical or
electrical failure in a reactor coolant pump, or from a fault in the power
supply to the pump or pumps supplied by a reactor coolant pump bus. If the reactor is at power at the time of the accident, the immediate effect of the
loss of coolant flow is a rapid increase in the coolant temperature. This
increase could result in departure from nucleate boiling (DNB) with subsequent
fuel damage if the reactor is not tripped promptly.
Normal power for the pumps is supplied through individual busses connected to
the generator. When a generator trip occurs, the busses are automatically
transferred to a transformer supplied from external power lines, and the pumps
will continue to operate. Following any turbine trip where there are no electrical faults or turbine faults which require immediate tripping of the generator from the network, the generator remains connected to the network for at least 30 seconds. The reactor coolant pumps remain connected to the generator, thus ensuring full flow for at least 30 seconds after the reactor trip before any transfer is made.
15.3-1 Rev. 25 WOLFCREEKApartiallossofcoolantflowisclassifiedasanANSConditionIIincident(afaultofmoderatefrequency),asdefinedinSection15.0.1.Thenecessaryprotectionagainstthiseventisprovidedbythelowprimarycoolantflowreactortripsignal,whichisactuatedinanyreactorcoolantloopbytwooutofthreelowflowsignals.AbovePermissive8(seeSection7.2), lowflowinanyloopwillactuateareactortrip.Betweenapproximately10-percentpower(Permissive7)andthepowerlevelcorrespondingtoPermissive8, lowflowinanytwoloopswillactuateareactortrip.AbovePermissive7,twoormorereactorcoolantpumpcircuitbreakersopeningwillactuatethecorrespondingundervoltagerelays.Thisresultsinareactortripwhichserves asabackuptothelowflowtrip.15.3.1.2AnalysisofEffectsandConsequencesMethodofAnalysisThecaseforalossoftworeactorcoolantpumpswithfourloopsinoperationisanalyzedhere.ThiseventisanalyzedbyemployingthedetaileddigitalcomputerprogramRETRAN-02(Ref1).RETRAN-02hasbeenfoundacceptablebytheNRCforuseasalicensingbasissafetyanalysiscode.RETRAN-02isathermal-hydraulicsystemsanalysiscodeemployingaone-dimensional,homogeneousequilibriummixture thermal-hydraulicmodelfortheRCS,apointkineticsmodelforthereactor core,specialcomponentandauxiliarymodels(ex.,pumps,temperaturetransport,non-equilibriumpressurizer)andcontrolsystemmodels.Thecodecomputespertinentplanttransientinformationincludingcorepowerlevel,RCSpressureandtemperature.VIPRE-01(Ref2)isusedtoevaluatethecorethermallimitstodetermineDNBR.RETRAN-02generatedstatepointsareusedasVIPRE-01boundaryconditionstoperformaStatisticalCoreDesign(SCD)DNBanalysis.InitialConditionsPlantcharacteristicsandinitialconditionsarediscussedinSection15.0.3.Thiseventisinitiatedatnominaloperatingconditionsinaccordancewith WestinghouseRTDPmethodology(Ref.4)toperformtheDNBanalysis15.3-2Rev.12 WOLFCREEKReactivityCoefficientsAconservativelylargeabsolutevalueoftheDoppler-onlypowercoefficientisused(seeFigure15.0-2),andthemostpositivemoderatortemperaturecoefficientisassumed,sincethisresultsinthemaximumcorepowerduringtheinitialpartofthetransient,whentheminimumDNBRisreached.Forthisanalysis,thecurveoftripreactivityinsertionversustime(Figure15.0-5)wasused.FlowCoastdownTheflowcoastdownanalysisisbasedonamomentumbalancearoundeachreactorcoolantloopandacrossthereactorcore.Thismomentumbalanceiscombinedwiththecontinuityequation,apumpmomentumbalance,andthepumpcharacteristics,andisbasedonhighestimatesofsystempressurelosses.MajorplantsystemsandequipmentavailableformitigationoftransientandaccidentconditionsarediscussedinSection15.0.8andlistedinTable15.0-6.Theactualparametersassumedandresultsaregivenintherespectivesection/subsection.Table15.0-6incorporateseventsshowninthesequencediagram,Figure15.0-15. ResultsFigures15.3-1through15.3-5showthetransientresponseforthelossoftworeactorcoolantpumpswithfourloopsinoperation.Figure15.3-6showstheDNBRtobealwaysgreaterthanthesafetyanalysislimit.Theplantistrippedbythelowflowtriprapidlyenoughtoensurethattheabilityofthereactorcoolanttoremoveheatfromthecoreisnotgreatly reducedforthecasesanalyzed.Thus,theaveragefuelandcladtemperatures donotincreasesignificantlyabovetheirrespectiveinitialvalues.15.3-3Rev.13 WOLF CREEK The calculated sequence of events table for the cases analyzed is shown on
Table 15.3-1. The affected reactor coolant pump(s) will continue to coast down, and the core flow will reach a new equilibrium value corresponding to the
two pumps still in operation. With the reactor tripped, a stable plant
condition will eventually be attained. Normal plant shutdown may then proceed.
15.3.1.3 Conclusions
The analysis shows that the DNBR will not decrease below the safety limit at
any time during the transient. The DNBR analysis design basis is described in
Section 4.4. All applicable acceptance criteria are met.
15.3.2 COMPLETE LOSS OF FORCED REACTOR COOLANT FLOW
15.3.2.1 Identification of Causes and Accident Description A complete loss of flow accident may result from a simultaneous loss of
electrical supplies to all reactor coolant pumps. If the reactor is at power at
the time of the accident, the immediate effect of loss-of-coolant flow is a rapid increase in the coolant temperature. This increase could result in a DNB
with subsequent fuel damage if the reactor were not tripped promptly.
Normal power for the reactor coolant pumps is supplied through busses from a
transformer connected to the generator. When a generator trip occurs, the
busses are automatically transferred to a transformer supplied from external
power lines, and the pumps will continue to supply coolant flow to the core.
Following any turbine trip where there are no electrical faults or turbine faults which require immediate tripping of the generator from the network, the generator remains connected to the network for at least 30 seconds. The reactor coolant pumps remain connected to the generator, thus ensuring full flow for at least 30 seconds after the reactor trip before any transfer is made. A complete loss of flow accident is classified as an ANS Condition III event (an infrequent fault), as defined in Section 15.0.1. The following signals
provide protection against this event:
- a. Reactor coolant pump power supply undervoltage or
underfrequency
- b. Low reactor coolant loop flow
15.3-4 Rev. 25 WOLFCREEKThereactortriponreactorcoolantpumpundervoltageisprovidedtoprotectagainstconditionswhichcancausealossofvoltagetoallreactorcoolantpumps.Thisfunctionisblockedbelowapproximately10-percentpower(Permissive7).Thereactortriponreactorcoolantpumpunderfrequencyisprovidedtotripthereactorforanunderfrequencycondition,resultingfromfrequencydisturbancesonthepowergrid.Reference3providesanalysesofgridfrequencydisturbancesandtheresultingNSSSprotectionrequirementswhichareapplicabletoWCGS.Reference3showsthattheunderfrequencytripofthereactorcoolantpumpbreakersisnotrequiredforgriddecayratesupto5Hz/sec.GridstabilityandtransientanalysesforboththeWolfCreekandCallawaysitesshowmaximum griddecayratesoflessthan5Hz/sec.Therefore,thereactorcoolantpump breakertriponunderfrequency(Figure7.2-1,Sheet5)isnotasafety functionintheWCGSdesign.Thereactortriponlowprimarycoolantloopflowisprovidedtoprotectagainstlossofflowconditionswhichaffectonlyonereactorcoolantloop.Thisfunctionisgeneratedbytwooutofthreelowflowsignalsperreactorcoolantloop.AbovePermissive8,lowflowinanyloopwillactuateareactortrip.Betweenapproximately10-percentpower(Permissive7)andthepowerlevelcorrespondingtoPermissive8,lowflowinanytwoloopswillactuatea reactortrip.Ifthemaximumgridfrequencydecayrateislessthanapproximately2.5Hertzpersecond,thistripfunctionwillprotectthecore fromunderfrequencyevents.ThiseffectisfullydescribedinReference3.15.3.2.2AnalysisofEffectsandConsequencesMethodofAnalysisThefollowingcasehasbeenanalyzed:LossoffourpumpswithfourloopsinoperationThemethodofanalysisandtheassumptionsmaderegardinginitialoperatingconditionsandreactivitycoefficientsareidenticaltothosediscussedin Section15.3.1,exceptthat,followingthelossofpowersupplytoallpumpsat power,areactortripisactuatedbyeitherreactorcoolantpumppowersupplyundervoltageorunderfrequency.15.3-5Rev.14 WOLFCREEK ResultsFigure15.3-8,basedonthePressureEvaluationModel,andFigures15.3-7and15.3-9through15.3-12,basedontheStatisticalCoreDesignModel,showthetransientresponseforthelossofpowertoallreactorcoolantpumpswithfourloopsinoperation.Thereactorisassumedtobetrippedonanundervoltagesignal.Figure15.3-12showstheDNBRtobealwaysgreaterthanthesafetyanalysislimit.Forthecaseanalyzed,theplantistrippedbytheundervoltagetripsufficientlyfasttoensurethattheabilityoftheprimarycoolanttoremoveheatfromthefuelrodisnotgreatlyreduced.Thus,theaveragefuelandclad temperaturesdonotincreasesignificantlyabovetheirrespectiveinitial values.ThecalculatedsequenceofeventsforthecaseanalyzedisshownonTable15.3-1.Thereactorcoolantpumpswillcontinuetocoastdown,andnatural circulationflowwilleventuallybeestablished,asdemonstratedinSection 15.2.6.Withthereactortripped,astableplantconditionwillbeattained. Normalplantshutdownmaythenproceed.15.3.2.3ConclusionsTheanalysisperformedhasdemonstratedthat,forthecompletelossofforcedreactorcoolantflow,theDNBRdoesnotdecreasebelowthesafetyanalysislimitatanytimeduringthetransient.ThedesignbasisfortheDNBRisdescribedinSection4.4.Allapplicableacceptancecriteriaaremet.15.3.3REACTORCOOLANTPUMPSHAFTSEIZURE(LOCKEDROTOR) 15.3.3.1IdentificationofCausesandAccidentDescriptionTheaccidentpostulatedisaninstantaneousseizureofareactorcoolantpumprotor,asdiscussedinSection5.4.Flowthroughtheaffectedreactorcoolantloopisrapidlyreduced,leadingtoaninitiationofareactortriponalowflowsignal.Followinginitiationofthereactortrip,heatstoredinthefuelrodscontinuestobetransferredtothecoolant,causingthecoolanttoexpand.Atthesametime,heattransfertotheshellsideofthesteamgeneratorsis reduced-first,becausethereducedflowresultsinadecreasedtubesidefilm coefficient,15.3-6Rev.13 WOLFCREEKandthen,becausethereactorcoolantinthetubescoolsdownwhiletheshellsidetemperatureincreases(turbinesteamflowisreducedtozerouponplanttrip).Therapidexpansionofthecoolantinthereactorcore,combinedwithreducedheattransferinthesteamgenerators,causesaninsurgeintothe pressurizerandapressureincreasethroughouttheRCS.Theinsurgeintothe pressurizercompressesthesteamvolume,actuatestheautomaticspraysystem, opensthepower-operatedreliefvalves,andopensthepressurizersafety valves,inthatsequence.Thetwopower-operatedreliefvalvesaredesigned forreliableoperation,andwouldbeexpectedtofunctionproperlyduringthe accident.However,forconservatism,theirpressure-reducingeffect,aswellas thepressure-reducingeffectofthespray,arenotincludedintheanalysis.ThiseventisclassifiedasanANSConditionIVincident(alimitingfault),asdefinedinSection15.0.1.15.3.3.2AnalysisofEffectsandConsequencesMethodofAnalysisTwodigitalcomputercodesareusedtoanalyzethistransient.TheRETRANcode(Ref.1)isusedtocalculatetheresultingloopandcoreflowtransientsfollowingthepumpseizure,thetimeofreactortripbasedontheloopflowtransients,thenuclearpowerfollowingreactortrip,andtodeterminethepeakpressure.ThethermalbehaviorofthefuellocatedatthecorehotspotisinvestigatedbyusingtheFACTRANcode(Ref.5),whichusesBishop-Sandberg-Tonfilmboilingcorrelationtoevaluatefluidproperties.15.3-7Rev.13 WOLFCREEKAccidentScenarioTwocasesareanalyzed:a.Onelockedrotorwithfourloopsinoperationwithoffsitepower.b.Onelockedrotorwithfourloopsinoperationwithoutoffsitepower.Thelockedrotortransientispostulatedtooccurinthefollowingmanner:a.Reactorcoolantpumprotorlocksandflowinthatloopbeginstocoastdown.b.ThereactoristrippedonlowRCSflowinoneloop.c.Turbinegeneratortrips. d.Offsitepowerislostforthewithoutoffsitepower case.NOTE:Gridstabilityanalysesshowthatthegridwillremainstableandoffsitepowerwillnotbelostbecauseofaunittripfrom100percentpower.RefertoSection8.2.2.Thefollowinganalysisassumesnotimedelaybetweenreactortripandlossofoffsitepower.Thisisa conservativeassumptionbasedonthegridstabilityanalyses.e.Thelossofoffsitepowercausesthethreeremainingreactorcoolantpumpstocoastdown.Atthebeginningofthepostulatedlockedrotoraccident,i.e.,atthetimetheshaftinoneofthereactorcoolantpumpsisassumedtoseize,theplantisassumedtobeinoperationunderthemostadversesteadystateoperatingconditions,i.e.,maximumguaranteedsteadystatethermalpower,maximumsteady statepressure,andmaximumsteadystatecoolantaveragetemperature.Plant characteristicsandinitialconditionsarefurtherdiscussedinSection15.0.3.Forthepeakpressureevaluation,theinitialpressureisconservativelysetat30psiabovenominalpressure(2,250psia)toallowforerrorsinthepressurizerpressuremeasurementandcontrolchannels.Thisisdonetoobtainthehighestpossibleriseinthecoolantpressureduringthetransient.Toobtainthemaximumpressureintheprimaryside,conservativelyhighlooppressuredropsareaddedtothecalculatedpressurizerpressure.15.3-8Rev.10 WOLFCREEKEvaluationofthePressureTransientAfterpumpseizure,theneutronfluxisrapidlyreducedbycontrolrodinsertion.Rodmotionisassumedtobegin1secondaftertheflowintheaffectedloopreaches87percentofnominalflow.Nocreditistakenforthepressure-reducingeffectofthepressurizerreliefvalves,pressurizerspray,steamdump,orcontrolledfeedwaterflowafterplanttrip.Althoughtheseoperationsareexpectedtooccurandwouldresultinalowerpeakpressure,anadditionaldegreeofconservatismisprovidedbyignoringtheireffect.EvaluationofDNBintheCoreDuringtheAccidentForthisaccident,DNBiscalculatedtooccurinthecoreand,therefore,anevaluationoftheconsequenceswithrespecttofuelrodthermaltransientsisperformed.Resultsobtainedfromanalysisofthis"hotspot"conditionrepresenttheupperlimitwithrespecttocladtemperatureandzirconium-water reaction.FilmBoilingCoefficientThefilmboilingcoefficientiscalculatedintheFACTRANcode(Ref.5),usingtheBishop-Sandberg-Tongfilmboilingcorrelation.Thefluidpropertiesareevaluatedatfilmtemperature(averagebetweenwallandbulktemperatures).Theprogramcalculatesthefilmcoefficientateverytimestep,basedupontheactualheattransferconditionsatthetime.Thenuclearpower,systempressure,bulkdensity,andmassflowrateasafunctionoftimeareusedas programinput.Forthisanalysis,theinitialvaluesofthepressureandthebulkdensityareusedthroughoutthetransient,sincetheyarethemostconservativewith respecttocladtemperatureresponse.Forconservatism,DNBwasassumedto startatthebeginningoftheaccident.15.3-9Rev.10 WOLFCREEKFuelCladGapCoefficientThemagnitudeandtimedependenceoftheheattransfercoefficientbetweenfuelandclad(gapcoefficient)haveapronouncedinfluenceonthethermalresults.Thelargerthevalueofthegapcoefficient,themoreheatistransferredbetweenpelletandclad.Basedoninvestigationsontheeffectofthegap coefficientuponthemaximumcladtemperatureduringthetransient,thegap coefficientwasassumedtoincreasefromasteadystatevalueconsistentwithinitialfueltemperatureto10,000Btu/hr-ft 2-°Fattheinitiationofthetransient.Thus,thelargeamountofenergystoredinthefuelbecauseofthesmallinitialvalueisreleasedtothecladattheinitiationofthetransient.Zirconium-SteamReactionThezirconium-steamreactioncanbecomesignificantabove1,800 °F(cladtemperature).TheBaker-Justparabolicrateequationshownbelowisusedtodefinetherateofthezirconium-steamreaction. d(w 2)dt=33.3X10 6 exp -45500 1.986T where:w=amountreacted,mg/cm 2t=time,secT=temperature,KThereactionheatis1,510cal/gm.Theeffectofzirconium-steamreactionisincludedinthecalculationofthe"hotspot"cladtemperaturetransient.MajorplantsystemsandequipmentavailableformitigationoftransientandaccidentconditionsarediscussedinSection15.0.8andlistedinTable15.0-6.Theactualparametersassumedandresultsaregivenintherespectivesection/subsection.Table15.0-6incorporateseventsshowninthesequencediagram,Figure15.0-15.Nosingleactivefailureinanyofthesesystemsorequipmentwilladverselyaffecttheconsequencesoftheaccident.ResultsandConclusionsFigures15.3-13,basedonthePressureEvaluationModel,andFigures15.3-14through15.3-19,basedontheStatisticalCoreDesignModel,showthetransientresultsforonelockedrotorwithandwithoutoffsitepowerwithfourloopsinoperation.TheresultsofthesecalculationsarealsosummarizedinTable 15.3-2.ThepeakRCSpressurereachedduringthetransientislessthan110%ofthedesignpressure.15.3-10Rev.13 WOLFCREEKAlso,thepeakcladsurfacetemperatureisconsiderablylessthan2,700 °F.Itshouldbenotedthatthecladtemperaturewasconservativelycalculated,assumingthatDNBoccursattheinitiationofthetransient.ThecalculatedsequenceofeventsforthetwocasesanalyzedisshownonTable15.3-1.Figures15.3-14and15.3-15showsthatthecoreflowrapidlyreachesanewequilibriumvalue.Withthereactortripped,astableplantconditionwill eventuallybeattained.Normalplantshutdownmaythenproceed.15.3.3.3RadiologicalConsequences15.3.3.3.1MethodofAnalysis15.3.3.3.1.1PhysicalModel Theinstantaneousseizureofareactorcoolantpumprotorresultsinareactortriponalowcoolantflowsignal.Withthecoincidentlossofoffsitepower,thecondensersarenotavailable,sotheexcessheatisremovedfromthesecondarysystembyasteamdumpthroughthesteamgeneratorsafetyand atmosphericreliefvalves.Steamgeneratortubeleakageisassumedtocontinueuntilthepressuresinthereactorcoolantandsecondarysystemsareequalized. ThereactorcoolantwillcontainthegapactivitiesofthefractionofthefuelwhichundergoesDNBinadditiontoitsassumedequilibriumactivity.15.3.3.3.1.2AssumptionsandConditionsThemajorassumptionsandparametersusedintheanalysisareitemizedinTables15.3-3and15A-1andsummarizedbelow.Theassumptionusedtodeterminetheinitialconcentrationsofisotopesinthereactorcoolantandsecondarycoolantpriortotheaccidentareasfollows:a.Thereactorcoolantiodineactivityisbasedonthedoseequivalentof1.0 µCi/gmofI-131.b.Thenoblegasactivityinthereactorcoolantisbasedon1-percentfailedfuel.15.3-11Rev.13 WOLFCREEKc.Thesecondarycoolantactivityisbasedonthedoseequivalentof0.1 µCi/gmofI-131.Thefollowingconditionsareusedtocalculatetheactivityreleased.a.5percentoffuelrodgapactivityisadditionallyreleasedtothereactorcoolant.b.Offsitepowerislost.c.Followingtheincident,secondarysteamisreleasedtotheenvironmentforheatremoval.ThetotalquantityofsteamreleasedisgiveninTable15.3-3.d.Primary-to-secondaryleakagecontinuesaftertheaccidentforaperiodof8hours.Atthattime,reactorcoolantandsecondarysystempressuresareequalized. Untilthepressureequalizes,theleakagerateis assumedtobeconstantandequaltotherateexistingpriortotheincidentof1gpm(500lbs/hr).e.Fissionproductsreleasedfromthefuel-claddinggapofthedamagedfuelrodsareassumedtobeinstantaneouslyandhomogeneouslymixedwiththereactorcoolant.f.Thenoblegasactivityreleasedisequaltotheamountpresentinthereactorcoolantwhichleaksintothesecondarysystemaftertheaccident.g.Theiodineactivitypresentintheprimarytosecondaryleakageisassumedtomixhomogeneouslywiththeiodine activityinitiallypresentinthesteamgenerators.h.Apartitionfactorof0.01betweenthevaporandliquidphasesforradioiodineinthesteamgeneratorsisutilizedtodetermineiodinereleasestotheenvironmentviasteamventingfromthesteamgenerators.i.Theactivityreleasedfromthesteamgeneratorsisimmediatelyventedtotheenvironment.j.Nocreditistakenforradioactivedecayorgrounddepositionduringradioactivitytransporttooffsite location.15.3-12Rev.13 WOLFCREEKk.Short-termaccidentatmosphericdispersionfactorscorrespondingtogroundlevelreleases,breathingrates,anddoseconversionfactorsaregiveninTable15A-2.15.3.3.3.1.3MathematicalModelsUsedintheAnalysisMathematicalmodelsusedintheanalysisaredescribedinthefollowing sections:a.ThemathematicalmodelsusedtoanalyzetheactivityreleasedduringthecourseoftheaccidentaredescribedinAppendix15A.b.TheatmosphericdispersionfactorsusedintheanalysiswerecalculatedbasedontheonsitemeteorologicalmeasurementprogramsdescribedinSection2.3andareprovidedinTable15A-2.c.Thethyroidinhalationandtotal-bodyimmersiondosestoareceptorattheexclusionareaboundaryorouterboundaryofthelow-populationzonewereanalyzedusing themodelsdescribedinAppendix15A.15.3.3.3.1.4IdentificationofLeakagePathwaysandResultantLeakageActivityTheleakagepathwaysare:a.Directsteamdumptotheatmospherethroughthesecondarysystematmosphericreliefandsafetyvalvesforthesecondarysteamb.Primary-to-secondarysteamgeneratortubeleakageandsubsequentsteamdumptotheatmospherethroughthesecondarysystematmosphericreliefandsafetyvalvesTable15.3-3showsthetotalcuriesreleased.15.3.3.3.2IdentificationofUncertaintiesandConservativeElementsintheAnalysisa.Reactorcoolantandsecondarycoolantactivitiesof1.0mCi/gmand0.1mCi/gmI-131doseequivalent,respectively,aremanytimesgreaterthanassumedfornormaloperationconditions.b.A1-gpmsteamgeneratorprimary-to-secondaryleakage,whichissignificantlygreaterthanthatanticipatedduringnormaloperation,isassumed.15.3-13Rev.13 WOLFCREEKc.Thecoincidentlossofoffsitepowerwiththeoccurrenceofareactorcoolantpumplockedrotorisahighlyconservativeassumption.Intheeventoftheavailabilityofoffsitestationpower,thecondenser steamdumpvalveswillopen,permittingsteamdumpto thecondenser.Thusthereisnodirectreleasetothe
environment.d.Themeteorologicalconditionswhichmaybepresentatthesiteduringthecourseoftheaccidentareuncertain.However,itishighlyunlikelythatthemeteorologicalconditionsassumedwillbepresentduringthecourseoftheaccidentforanyextendedperiodof time.Therefore,theradiologicalconsequencesevaluated,basedonthemeteorologicalconditionsassumed,areconservative.15.3.3.3.3Conclusions15.3.3.3.3.1FilterLoadings TheonlyESFfiltrationsystemconsideredintheanalysiswhichlimitstheconsequencesofthereactorcoolantpumplockedrotoraccidentisthecontrolroomfiltrationsystem.Activityloadingsonthecontrolroomcharcoalfilterarebasedontheflowratethroughthefilter,theconcentrationofactivityatthefilterinlet,andthefilterefficiency.Theactivityinthecontrolroomfilterasafunctionoftimehasbeenevaluatedfortheloss-of-coolantaccident,Section15.6.5.Sincethecontrolroomfiltersarecapableofaccommodatingthepotentialdesign-basisloss-of-coolantaccidentfissionproductiodineloadings,morethanadequatedesign marginisavailablewithrespecttopostulatedreactorcoolantpumplocked rotoraccidentreleases.15.3.3.3.3.2DosestoReceptorattheExclusionAreaBoundaryandLow-PopulationZoneOuterBoundaryThepotentialradiologicalconsequencesresultingfromtheoccurrenceofapostulatedreactorcoolantpumplockedrotorhavebeenconservativelyanalyzed, usingassumptionsandmodelsdescribedinprevioussections.Thetotal-bodydosesduetoimmersionfromdirectradiationandthethyroiddoseduetoinhalationhavebeenanalyzedforthe0-2hourdoseatthe exclusionareaboundaryandforthedurationoftheaccident(0to8hours)at thelow-populationzoneouterboundary.TheresultsarelistedinTable15.3-4.Theresultantdosesarewellwithintheguidelinevaluesof10CFR100.15.3-14Rev.12 WOLFCREEK15.3.3.4Conclusionsa.SincethepeakRCSpressurereachedduringanyofthetransientsislessthanthatwhichwouldcausestressestoexceedthefaultedconditionstresslimits,theintegrityoftheprimarycoolantsystemisnot
endangered.b.Sincethepeakcladsurfacetemperaturecalculatedforthehotspotduringtheworsttransientremainsconsiderablylessthan2,700 °F,thecorewillremaininplaceandintactwithnolossofcorecooling capability.15.3.4REACTORCOOLANTPUMPSHAFTBREAK15.3.4.1IdentificationofCausesandAccidentDescriptionTheaccidentispostulatedasaninstantaneousfailureofareactorcoolantpumpshaft,asdiscussedinSection5.4.Flowthroughtheaffectedreactor coolantloopisrapidlyreduced,thoughtheinitialrateofreductionofcoolantflowisgreaterforthereactorcoolantpumprotorseizureevent.Reactortripisinitiatedonalowflowsignalintheaffectedloop.Followinginitiationofthereactortrip,heatstoredinthefuelrodscontinuestobetransferredtothecoolant,causingthecoolanttoexpand.At thesametime,heattransfertotheshellsideofthesteamgeneratorsisreduced-first,becausethereducedflowresultsinadecreasedtubesidefilm coefficientandthenbecausethereactorcoolantinthetubescoolsdownwhile theshellsidetemperatureincreases(turbinesteamflowisreducedtozerouponplanttrip).Therapidexpansionofthecoolantinthereactorcore, combinedwithreducedheattransferinthesteamgenerators,causesaninsurge intothepressurizerandapressureincreasethroughouttheRCS.Theinsurge intothepressurizercompressesthesteamvolume,actuatestheautomaticspraysystem,opensthepower-operatedreliefvalves,andopensthepressurizersafetyvalves,inthatsequence.Thetwopower-operatedreliefvalvesaredesignedforreliableoperationandwouldbeexpectedtofunctionproperlyduringtheaccident.However,forconservatism,theirpressure-reducing effect,aswellasthepressure-reducingeffectofthespray,arenotincluded intheanalysis.ThiseventisclassifiedasanANSConditionIVincident(alimitingfault),asdefinedinSection15.0.1.15.3-15Rev.0 WOLFCREEK15.3.4.2ConclusionsTheconsequencesofareactorcoolantpumpshaftbreakarenoworsethanthosecalculatedforthelockedrotorincident(seeSection15.3.3).Withafailedshaft,theimpellercouldconceivablybefreetospininareversedirectionasopposedtobeingfixedinpositionasassumedinthelockedrotoranalysis. However,theneteffectoncoreflowisnegligible,resultinginonlyaslight decreaseintheendpoint(steadystate)coreflow.Forboththeshaftbreakandlockedrotorincidents,reactortripoccursveryearlyinthetransient.Inaddition,thelockedrotoranalysisconservativelyassumesthatDNBoccurs atthebeginningofthetransient.15.
3.5REFERENCES
1.McFadden,J.H.,et.al.,"RETRAN-02-AProgramforTransientThermalHydraulicAnalysisofComplexFluidFlowSystems,"EPRINP-1850-CCM-A,October 1984.2.Stewart,C.W.,et.al.,"VIPRE-01:AThermal-HydraulicCodeforReactorCores,"Battelle,PacificNorthwestLaboratories,EPRINP-2511-CCM-A,August 1989.3.Baldwin,M.S.,Merrian,M.M.,Schenkel,H.S.andVanDeWalle,D.J.,"AnEvaluationofLossofFlowAccidentsCausedbyPowerSystemFrequencyTransientsinWestinghousePWRs,"WCAP-8424,Revision1,May1975.4.WCAP-11397-P-A,"RevisedThermalDesignProcedure,"A.J.Fiedland,etal.,April19895.Hargrove,H.G.,"FACTRAN-AFORTRAN-IVCodeforThermalTransientsinaUO2FuelRod,"WCAP-7908A,December1989.15.3-16Rev.10 WOLF CREEK TABLE 15.3-1 TIME SEQUENCE OF EVENTS FOR INCIDENTS WHICH RESULT IN A DECREASE IN REACTOR COOLANT SYSTEM FLOW RATE TimeAccidentEvent (sec)Partial loss of forced reactor coolant flow1.Loss of two pumps with four loops inoperationCoastdown begins0.0 Low flow reactor trip2.21 Rods begin to drop3.21 Minimum DNBR occurs3.8 Complete loss of forced reactor coolant flow1.Loss of four pumps with four loops in operationAll operating pumps0.0 lose power and begin coasting down Reactor coolant pump0.0 undervoltage trip point reached Rods begin to drop1.5 Minimum DNBR occurs3.5 Rev. 10 WOLF CREEK TABLE 15.3-1 (Sheet 2) TimeAccidentEvent (sec)Reactor coolant pump shaft seizure (locked
rotor)1.One locked rotor with four loops in operation W/ offsite powerRotor on one pump0.0 locks Low flow trip point1.04 reached Rods begin to drop2.04 Maximum RCS3.8 pressure occurs2.One locked rotor with four loops in operation W/O offsite powerRotor on one pump0.0
locks Low flow trip point1.04 reached Rods begin to drop2.04 Power lost to remaining3.04 pumps Maximum RCS4.7 pressure occurs Rev. 10 WOLF CREEK TABLE 15.3-2
SUMMARY
OF RESULTS FOR LOCKED ROTOR TRANSIENTS With Offsite Power Without Offsite Power Maximum reactor coolant system pressure, psia 2580 2591 Maximum clad temperature, °F, core hot spot 1938 1942 Zr-H 2 O reaction at core hot spot, percent by weight0.360.40`Rev. 10 WOLF CREEK TABLE 15.3-3 PARAMETERS USED IN EVALUATING THE RADIOLOGICAL CONSEQUENCES OF A LOCKED ROTOR ACCIDENTI.Source Dataa. Power level, MWt3,565b. Steam generator tube1 leakage, gpmc. Reactor coolant iodineDose equivalent of activity 1.0 µCi/gm of I-131d. Reactor coolant noble gasBased on 1-percentactivityfailed fuel, as provided in Table 11.1-5e.Secondary system activityDose equivalent of 0.1µCi/gm of I-131f.Activity released to reactor coolant from failed fuel 1.Noble gas, percent of gap5 inventory2.Iodine, percent of gap5 inventory3.Gap inventoryTable 15A-3g.Iodine partition factor for0.01 steam generatorsh.Reactor coolant mass, lbs4.94E+5i.Steam generator mass,9.55E+4 per generator, lbsII.Atmospheric Dispersion Factorssee Table 15A-2III.Activity Release Dataa.Steam discharge, 0-2 hrs1.Reactor coolant leakage,1,000 lbs2.Mass released from steam5.49E+5 generators, lbsb.Steam discharge, 2-8 hrs1.Reactor coolant leakage,3,000 lbs2.Mass released from steam1.03E+6 generators, lbs Rev. 13 WOLF CREEK TABLE 15.3-3 (Sheet 2)c.Activity released to the environmentIsotope0-2 hr (Ci)0-8 hr (Ci)I-1318.378.36E+1I-1326.862.63E+1I-1331.38E+11.23E+2I-1345.879.88I-1351.17E+18.15E+1Xe-131m1.17E+14.66E+1Xe-133m6.30E+12.42E+2Xe-1332.09E+38.24E+3Xe-135m6.99E+17.02E+1Xe-1354.45E+21.44E+3Xe-1378.02E+18.02E+1Xe-1382.81E+22.82E+2Kr-83m8.82E+11.58E+2Kr-85m2.33E+26.23E+2Kr-853.52E+11.41E+2Kr-873.19E+24.74E+2Kr-885.85E+21.30E+3Kr-893.43E+13.43E+1 Rev. 13 WOLF CREEK TABLE 15.3-4 RADIOLOGICAL CONSEQUENCES OF A LOCKED ROTOR ACCIDENT Wolf Creek Dose (rem) Exclusion Area Boundary (0-2 hr)Thyroid, rem0.882Whole body, rem0.076 Low Population ZoneOuter Boundary (duration)Thyroid, rem1.130Whole body, rem0.021 Rev. 13 WOLF CREEK TABLE 15.3-5 THI S TABLE HA S BEEN DELETED Rev. 6
2,2000 2 4 6 8 Rev. 10 UPDATED SAPBTY AHALYSIS RBPORT PIGURB 15.3-1 PRBSSURIZBR PRBSSURB TIWISIDT FOR POOR LOOPS IN OPERATION, TIIO PUMPS COASTING DOWN 10 I ,. { _, 1.05,.------------------------, i 1 :1 0.95 0.9 0.85 1!:. 0.8 0.75 0.7 .__ ______ ......_ _ _,_ _______ --:., ___ __;,_____, 0 2 . ..,.. 4 6 8 nME (SECONDS) Rev. 10 WOLF CRBElt UPDATED SAPBTY ANALYSIS RBPORT FIGURB 15.3-2 T0'1'AL CORB PLOW TRANSIENT POR FOtJR LOOPS IN OPERATIOS, TWO PUMPS COASTING D01IR 10 Rev. 10 WOLF CRBBK 'CPDATBD SAPETY ANALYSIS RBPOR.T PIGORB 15.3-3 FAULTED LOOP FLOW TRAHSIBN'l' FOR FOtJR LOOPS IN OPBRATIOl'f, TWO PUMPS COASTING DOWN *j 2 4 6 8 11ME (SECONDS) Rev. 10 WOLP CRBBK UPDATED SAi'BTY ANALYSIS REPORT PIGtJRB 15.3-4 NUCLBAR PONBR. TRANSIENT FOR. FOUR LOOPS DJ OPERATION, TWO PUMPS COASTING DOWN 10 G 1.1 I!J 1: io.e 1: 0.30 2 4 8 8 10 'lllllelaiiCIII Rev. 10 WOLP CRBBK OPDATBD SAPETr ANALYSIS REPORT FIGURE 15.3-S CORB HKAT FLOX AND CORB AVERAGB TBMPBRA'l'ORB POR POOR LOOPS IN OPBRA.T!Olf, TWO PDMPS COASTING D01fR
- . ; !"
1.9 .......... ......... .......... __ ........ --'-............... 0 1 2 3 4 5 11ME (SECONlS) Rev. 10 WOLI' CRBB1t tJPDATBD SAPBTY AHALYSIS RBPORT P'IGURB 15.3-6 DHBlt TRARSIBRT POR POUR. LOOPS Dr OPBRA'l'lOR, "l'MM PUMPS CDASTIJIQ D01Ill u L* i 1 0.9 0.8 fi 0.7 -§ 0.8 ii! 0.5 0 2 *""7* 4 8 8 llME (SECONDS) Rev. 10 WOLP CRBB1t UPDATED SAFB"1'Y ANALYSIS RBPORT FIGtJRB 15.3-7 'l'O'l'AL CORB PLOW TRANSIBHT POR FOUR LOOPS IB OPBRATION, POOR PUMPS COAS'l'IBG DOII1f 10 WOLI' CRUIC 2.550r-----------------------, 2,500 .. I ! 2.450
- I A. 2,400 .. I :I .1 2.350 A. 2,300 2,250 ...................
&...&..1. ............ .......... -'-'-.&....l..l.....&...&....l..&..ol .......... 0 1 2 3 4* 5 6 7 8 9 10 Time (seconds) Rev.13 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.3-8 PRESSURIZER PRESSURE TRANSIENT FOR FOUR LOOPS IN OPERA nON, FOUR PUMPSOOA&nNGDOWN G 1.2 -1 0.8 § 0.8 i -0.2 8 0 0 2 4 8 8 TIME (SECONDS) Rev. 10 WOLP CRBEIC UPDATED SAFETY ANALYSIS REPORT FIGORB 15.3-9 NORMALIZBD CORE POWBR TRANSIDT POR POOR LOOPS IN OPERATION, FO'OR PUMPS COASTING DOWN 10 2 4 8 8 11ME (SECONDS) Rev. 10 WOLP CRBBX OPDATBD SAPBTY ANALYSIS RBPORT FIGORB 15.3*10 CORB HEAT FLUX TRANSIBR'l' POR POUR LOOPS IN OPBRATION, 1'0tm PUMPS COASTING DOWR 10 v 2 4 6 8 TIME (SECONDS) Rev. 10 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.3-11 CORE AVERAGE TEMPERATURE FOR FOUR LOOPS IN OPERATION, FOUR PUMPS COASTING DOWN 10 2.5 2.4 2.3 12.2 c 2.1 :::') :::& z 2 2 1.9 1.8 1.7 0 1 2 3 4 11ME (SECONDS) Rev. 10 WOLP CREEK UPDATBD SAFB'l'Y ARALYSIS RBPORT FIGURB 15.3-12 DNBR TRAHSIBRT FOR POUR. LOOPS IN OPERATION, FOUR PUMPS COASTING DOWN v 5 v v L* 2.700 2,650 -2,800 .!1 A 2,550 1.2,500 12.450 12,350 2,300 2,250 2,200 0 1 2.600 2,650 12,500 -52,450
- l2..COO Juao 2.300 .2,2000 1 WOLF CREEK With atrsn. Poww 2 3 4 5 e 7 8 9 10 Time (eec:oncls)
Without Olfslll Power 2 3 4 5 6 7 8 9 10 nm. (IKOIIds) Rev.13 WOLFCREEK UPDATED SAFElY ANALYSIS REPORT
- FIGURE 18.3-13 PEAK RCS PRESSURE TRANSIENT LOCKED ROTOR WITH AND WITHOUT OFFS1TE POWER
i 0.9 0.8 f-§ 0.7 -0.6 r-** ... ....... .... ..... ... u. ...... .. ..... ...... ..... , ........ ..... ...... .............. 0.5 0.4 _ _....:. __ .:...._ _____ 0 2 8 10i<.. U Rev. 10 NOLP CRBBK UPDATED SAPBTY ARALYSIS REPORT PIGURB 15.3-14 TOTAL CORE FLOW TRANSIENT LOCKED ROTOR WITH AND WITHOUT OFPSITB POWER L* -1.2 1 --z u. 0.8 0 0.6 0.4 -0.2 f-IL 0 (0.2) -;...., (0.4) u.;; 0 2 ... I I 4 6 8 TIME (SECONDS) Rev. 10 WOLF CRBEK UPDA'l'BD. SAPETY ANALYSIS REPORT FIGORS 15.3*15 FAULTED LOOP FLOW TRANSIBN'l' LOCKED ROTOR WITM AND Wl:TBOUT OPFSITB PONBR 10 1.2...-----------------------, 2 WO+SliE FOt'ER WO OFFSI'IEPO.M:R 4 6 8 10 11ME (SECONDS) Rev. 10 UPDATED SAFETY ARALYSIS RBPORT PIGORB 15.3-16 NORMALIZED POWER TlWJSIDT LOC1t!D ROTOR WITS A!m WI'l'HO'CJT OFPSITB POWER 1.2 r-----------------------, i 1 z 0.6 WOFFSI IE POVIER WO a=FSII E POIIIER -0.4 0 2 4 6 8 10 TIME (SECONDS) Rev. 10 WOLF CRBEK UPDATED SAPB'lT ARALYSIS REPORT FIGtJRB 15.3-17 CORE HEAT P'LtrX TRARSIBNT LOCKBD ROTOR WI:TH AND WI'l'ROtrr OPPSITB POWER
G:' fas95 c -;. '* .... .. *, ... .. ... .... ... .. ... ..... ........... 0 2 4 8 8 llME (SECONDS) Rev. 10 WOLP CUB1t UPDATBD SAPBTY ANALYSIS RBPORT PIG'DRB 15.3-18 CORB AVERAGE 'l'BMPBRATORB LOCKED ROTOR WITH AND WITBOM' OFFSITE POWER 10 1,800 G:' c; 1,600 li 1,400 i 1.200 !! 1,000 I!! 800 600 2 4 8 8 TIME (SECONDS) Rev. 10 WOLP CRBBK UPDATED SAFBTY ANALYSIS REPORT PIGORB 1.5.3-1.9 O'OTER CLAD TBMPEM.TtJRB FOR LOCDD ROTOR WITHouT OPPSITB P01IBR 10 WOLF CREEK 15.4 REACTIVITY AND POWER DISTRIBUTION ANOMALIES A number of faults have been postulated which could result in reactivity and power distribution anomalies. Reactivity changes could be caused by control
rod motion or ejection, boron concentration changes, or addition of cold water
to the reactor coolant system (RCS). Power distribution changes could be
caused by control rod motion, misalignment, or ejection, or by static means such as fuel assembly mislocation. These events are discussed in this section.
Detailed analyses are presented for the most limiting of these events. Discussions of the following events are presented in this section:
- a. Uncontrolled rod cluster control assembly bank withdrawal from a subcritical or low power startup condition
- b. Uncontrolled rod cluster control assembly bank withdrawal at power
- c. Rod cluster control assembly misalignment
- d. Startup of an inactive reactor coolant pump at an incorrect temperature
- e. A malfunction or failure of the flow controller in a BWR recirculation loop that results in an increased reactor coolant flow rate (not applicable to Wolf Creek)
- f. Chemical and volume control system malfunction that results in a decrease in the boron concentration in the reactor coolant
- g. Inadvertent loading and operation of a fuel assembly in an improper position
- h. Spectrum of rod cluster control assembly ejection accidents Items a, b, d, and f above are considered to be ANS Condition II events; item g, an ANS Condition III event; and item h, an ANS Condition IV event. Item c
entails both Conditions II and III events. Section 15.0.1 contains a
discussion of ANS classifications. All of the accidents in this section have been analyzed. It has been determined that the most severe radiological consequences result from the
complete rupture of a control rod drive mechanism housing provided in Section 15.4.8. Therefore, radiological consequences are reported only for that limiting case. 15.4-1 Rev. 0 WOLF CREEK 15.4.1 UNCONTROLLED ROD CLUSTER CONTROL ASSEMBLY BANK WITHDRAWAL FROM A SUBCRITICAL OR LOW POWER STARTUP
CONDITION 15.4.1.1 Identification of Causes and Accident Description A rod cluster control assembly (RCCA) withdrawal accident is defined as an uncontrolled addition of reactivity to the reactor core caused by withdrawal of
RCCAs, resulting in a power excursion. Such a transient could be caused by a
malfunction of the reactor control or rod control systems. This could occur
with the reactor subcritical, at hot zero power or at power. The "at power" case is discussed in Section 15.4.2. Although the reactor is normally brought to power from a subcritical condition by means of RCCA withdrawal, initial startup procedures with a clean core call
for boron dilution. The maximum rate of reactivity increase in the case of boron dilution is less than that assumed in this analysis (see Section 15.4.6). The RCCA drive mechanisms are wired into preselected bank configurations which are not altered during reactor life. These circuits prevent the RCCAs from being automatically withdrawn in other than their respective banks. Power supplied to the banks is controlled so that no more than two banks can be withdrawn at the same time and in their proper withdrawal sequence. The RCCA
drive mechanisms are of the magnetic latch type, and coil actuation is
sequenced to provide variable speed travel. The maximum reactivity insertion
rate analyzed in the detailed plant analysis is that occurring with the
simultaneous withdrawal of the combination of two sequential control banks
having the maximum combined worth at maximum speed. This event is classified as an ANS Condition II incident (a fault of moderate frequency), as defined in Section 15.0.1. The neutron flux response to a continuous reactivity insertion is characterized by a very fast rise terminated by the reactivity feedback effect of the
negative Doppler coefficient. This self-limitation of the power excursion is
of primary importance, since it limits the power to a tolerable level during the delay time for protective action. Should a continuous RCCA withdrawal accident occur, the transient will be terminated by the following automatic
features of the reactor protection system: 15.4-2 Rev. 0 WOLF CREEK
- a. Source range high neutron flux reactor trip This trip function is actuated when either of two independent source range channels indicates a neutron flux level above a preselected manually adjustable setpoint. It may be manually bypassed only after an
intermediate range flux channel indicates a flux level
above a specified level. It is automatically reinstated
when both intermediate range channels indicate a flux
level below a specified level.
- b. Intermediate range high neutron flux reactor trip
This trip function is actuated when either of two independent intermediate range channels indicates a flux level above a preselected manually adjustable setpoint. It may be manually bypassed only after two out of the
four power range channels are reading above approximately 10 percent of full power, and is automatically reinstated when three out of the four channels indicate a power level below this value.
- c. Power range high neutron flux reactor trip (low setting)
This trip function is actuated when two out of the four power range channels indicate a power level above approximately 25 percent of full power. It may be manually bypassed when two out of the four power range
channels indicate a power level above approximately 10 percent of full power, and is automatically reinstated only after three out of the four channels indicate a power level below this value.
- d. Power range high neutron flux reactor trip (high setting)
This trip function is actuated when two out of the four power range channels indicate a power level above a
preset setpoint. It is always active.
- e. High nuclear flux rate reactor trip
This trip function is actuated when the positive rate of change of neutron flux on two out of four nuclear power
range channels indicates a rate above the preset
setpoint. It is always active. 15.4-3 Rev. 0 WOLF CREEK In addition, control rod stops on high intermediate range flux level (one out of two) and high power range flux level (one out of four) serve to discontinue
rod withdrawal and prevent the need to actuate the intermediate range flux
level trip and the power range flux level trip, respectively. 15.4.1.2 Analysis of Effects and Consequences Method of Analysis The analysis of the uncontrolled RCCA bank withdrawal from subcritical accident is performed in three stages: first an average core nuclear power transient
calculation, then an average core heat transfer calculation, and finally the
departure from nucleate boiling ratio (DNBR) calculation. The average core
nuclear calculation is performed, using spatial neutron kinetics methods, TWINKLE (Ref. 1), to determine the average power generation with time, including the various total core feedback effects, i.e., Doppler reactivity and
moderator reactivity. In the second stage, the average heat flux and
temperature transients are determined by performing a fuel rod transient heat transfer calculation in FACTRAN (Ref. 2). VIPRE-01 (Ref 14) is used to evaluate the core thermal limits to determine DNBR. Plant characteristics and initial conditions are discussed in Section 15.0.3. To give conservative results for a startup accident, the following assumptions
are made:
- a. Since the magnitude of the power peak reached during the initial part of the transient for any given rate of reactivity insertion is strongly dependent on the
Doppler coefficient, conservatively low values are used. This does not correlate to Figure 15.0-2 since the TWINKLE computer code, on which the neutronics analysis is based, is a diffusion theory code rather than a point-kinetics approximation.
- b. Contribution of the moderator reactivity coefficient is negligible during the initial part of the transient because the heat transfer time between the fuel and the moderator is much longer than the neutron flux response time. However, after the initial neutron flux peak, the
succeeding rate of power increase is affected by the moderator reactivity coefficient. A conservative value
is used in the analysis to yield the maximum peak heat
flux. 15.4-4 Rev. 7 WOLF CREEK
- c. The reactor is assumed to be at hot zero power (557 F average coolant temperature). This assumption is more
conservative than that of a lower initial system
temperature. The higher initial system temperature
yields a larger fuel-water heat transfer coefficient, larger specific heats, and a less negative (smaller absolute magnitude) Doppler coefficient, all of which tend to reduce the Doppler feedback effect, thereby
increasing the neutron flux peak. The initial effective multiplication factor (k eff) is assumed to be 1.0, since this results in the worst nuclear power transient.
- d. Reactor trip is assumed to be initiated by power range high neutron flux (low setting). The most adverse combination of instrument and setpoint errors, as well as delays for trip signal actuation and RCCA release, is taken into account. A 10-percent error increase is
assumed for the power range flux trip setpoint, raising it from the nominal value of 25 percent to 35 percent. Since the rise in the neutron flux is so rapid, the
effect of errors in the trip setpoint on the actual time
at which the rods are released is negligible. In
addition, the reactor trip insertion characteristic is based on the assumption that the highest worth RCCA is stuck in its fully withdrawn position. See Section
15.0.5 for RCCA insertion characteristics.
- e. The maximum positive reactivity insertion rate assumed is greater than that for the simultaneous withdrawal of the
combination of the two sequential control banks having the greatest combined worth at maximum speed (45
inches/minute). Control rod drive mechanism design is discussed in Section 4.6.
- f. The most limiting axial and radial power shapes, associated with having the two highest combined worth banks in their high worth position, are assumed in the
DNB analysis.
- g. The initial power level is assumed to be below the power level expected for any shutdown condition (10
-9 of nominal power). The combination of highest reactivity insertion rate and lowest initial power produces the
highest peak heat flux.
- h. Two reactor coolant pumps are assumed to be in operation.
15.4-5 Rev. 0 WOLF CREEK Major plant systems and equipment available for mitigation of transient and accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6. The actual parameters assumed and results are given in the respective section/subsection. Table 15.0-6 incorporates events shown in the sequence diagram, Figure 15.0-16. Results Figures 15.4-1 through 15.4-3 show the transient behavior for the uncontrolled RCCA bank withdrawal accident, with the accident terminated by reactor trip at
35 percent of nominal power. The reactivity insertion rate used is greater
than that calculated for the two highest worth sequential control banks, both
assumed to be in their highest incremental worth region. Figure 15.4-1 shows the average neutron flux transient.
The energy release and the fuel temperature increases are relatively small. The thermal flux response, of interest for DNB considerations, is shown on Figure 15.4-2. The beneficial effect of the inherent thermal lag in the fuel
is evidenced by a peak heat flux much less than the full power nominal value.
There is a large margin to DNB during the transient, since the rod surface heat
flux remains below the design value, and there is a high degree of subcooling
at all times in the core. Figure 15.4-3 shows the response of the hot spot
average fuel and inner cladding temperature. The average fuel temperature
increases to a value lower than the nominal full power value. The minimum DNBR
at all times remains above the limiting value. The calculated sequence of events for this accident is shown in Table 15.4-1. With the reactor tripped, the plant returns to a stable condition. The plant
may subsequentlÿ be cooled down further by following normal plant shutdown procedures. 15.4.1.3 Conclusions In the event of an RCCA withdrawal accident from the subcritical condition, the core and the RCS are not adversely affected, since the combination of thermal
power and the coolant temperature result in a DNBR greater than the limiting
value. The DNBR design basis is described in Section 4.4; applicable
acceptance criteria have been met. 15.4-6 Rev. 13 WOLF CREEK 15.4.2 UNCONTROLLED ROD CLUSTER CONTROL ASSEMBLY BANK
WITHDRAWAL AT POWER
15.4.2.1 Identification of Causes and Accident Description
Uncontrolled RCCA bank withdrawal at power (RWAP) results in an increase in the core heat flux. Since the heat extraction from the steam generator lags behind
the core power generation until the steam generator pressure reaches the relief
or safety valve setpoint, there is a net increase in the reactor coolant
temperature. Unless terminated by manual or automatic action, the power
mismatch and resultant coolant temperature rise could eventually result in DNB, overpressure, or a more severe accident. Therefore, to avert damage to the fuel clad or pressure boundary, the reactor protection system is designed to terminate any such transient before the DNBR falls below the safety analysis
limit or the pressure boundary is threatened by over pressure.
This event is classified as an ANS Condition II incident (a fault of moderate
frequency), as defined in Section 15.0.1.
The automatic features of the reactor protection system which prevent core damage following the postulated accident include the following:
- a. Power range neutron flux instrumentation actuates a
reactor trip if two out of four channels exceed any
overpower setpoint.
- b. A reactor trip actuated if any two out of four T channels exceed the overtemperature T setpoint. This setpoint is automatically varied with axial power imbalance, coolant temperature, and pressure to protect against DNB.
- c. A reactor trip actuated if any two out of four T channels exceed the overpower T setpoint. This setpoint is automatically varied with axial power imbalance to ensure that the allowable heat generation
rate (kW/ft) is not exceeded.
- d. A high pressurizer pressure reactor trip actuated from any two out of four pressure channels which are set at a
fixed point. This set pressure is less than the set
pressure for the pressurizer safety valves.
- e. A high pressurizer water level reactor trip actuated
from any two out of three level channels when the
reactor power is above approximately 10 percent
(Permissive 7).
- f. A power range neutron flux positive flux rate trip actuates a reactor trip if two out of four channels exceed any flux rate trip setpoint.
15.4-7 Rev. 25 WOLF CREEK In addition to the above listed reactor trips, there are the following RCCA
withdrawal blocks:
- a. High neutron flux (one out of four power range)
- b. Overpower T (two out of four)
- c. Overtemperature T (two out of four)
The area of permissible operation (power, pressure, and temperature) is bounded by the combination of reactor trips: high neutron flux (fixed setpoint); high pressure (fixed set-point); low pressure (fixed setpoint); neutron flux high positive flux rate trip (fixed rate setpoint) and overpower and overtemperature T (variable setpoints). 15.4.2.2 Analysis of Effects and Consequences Method of Analysis
The RWAP transients are analyzed by employing the digital computer program RETRAN-3D in the RETRAN-02 mode (Ref. 19). VIPRE-01 (Ref. 14) is used to evaluate the core thermal limits to determine DNBR. RETRAN-3D in the RETRAN-02 mode generated state points are used as VIPRE-01 boundary conditions to perform a Statistical Core Design (SCD) DNB
analysis. RETRAN-3D in the RETRAN-02 mode also directly evaluated the potential for overpressure and threats to the primary pressure boundary.
Plant characteristics and initial conditions are discussed in Section 15.0.3.
To obtain conservative results for an uncontrolled RCCA bank withdrawal at
power accident, the following assumptions are made:
- a. Initial conditions of a spectrum of core powers up to nominal core power (10%, 60%, and 100%), nominal reactor coolant temperatures, and nominal reactor coolant pressure are assumed to perform an SCD DNB analysis (see section 15.0.3). Initial conditions of a spectrum of core powers (5%, 10%, 60%, and 102%), maximum reactor coolant temperature, and maximum reactor coolant pressure are assumed to perform an RCS overpressurization and pressurizer fill analysis (see section 15.0.3).
- b. Reactivity coefficients - two conditions are analyzed:
- 1. Minimum reactivity feedback
A most positive moderator coefficient of
reactivity is assumed, corresponding to the beginning of core life. A variable Doppler power
coefficient with core power is used in the
analysis. A conservatively small (in absolute
magnitude) value is assumed.
- 2. Maximum reactivity feedback
A conservatively large positive moderator density coefficient (0.50 dk/gm/CC) and a large (in absolute magnitude) Doppler power coefficient are assumed.
15.4-8 Rev. 25 WOLF CREEK
- c. The reactor trip on high neutron flux is assumed to be
actuated at a conservative value of 118 percent of nominal full power. The T trips include all adverse instrumentation and setpoint errors; the delays for trip actuation are assumed to be the maximum values.
- d. The RCCA trip insertion characteristic is based on the
assumption that the highest worth assembly is stuck in
its fully withdrawn position.
- e. A range of reactivity insertion rates (1, 5, 10, 30, 40, 60, 80, and 100 pcm/sec) is examined. The maximum assumed positive reactivity insertion rate is greater than that for the simultaneous withdrawal of the combination of the two control banks, having the maximum combined worth at maximum speed.
- f. Reactivity insertion rates were varied in unit increments to determine the limiting condition for peak pressure, pressurizer fill, and power to flow ratio (DNB).
- g. The high neutron flux positive rate trip is assumed to be actuated at a conservative response lag, setpoint, and trip delay of 2 seconds, 9%/sec, and 3 seconds respectively.
The effect of RCCA movement on the axial core power distribution is accounted for by causing a decrease in overtemperature T trip setpoint proportional to a decrease in margin to DNB. Major plant systems and equipment available for mitigation of transient and
accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6.
The actual parameters assumed and results are given in the respective
section/subsection. Table 15.0-6 incorporates events shown in the sequence
diagram, Figure 15.0-16.
Results Figures 15.4-4a through 15.4-4g show the transient results of the limiting DNB analysis of the RWAP accident event. The limiting conditions are end of life, 100% rated thermal power and 39 pcm/sec reactivity addition rate resulting in a minimum DNBR of 1.86. Primary protection over the range of DNB cases analysis is high neutron flux and overtemperature . With high flux providing protection for the faster transients (high reactivity addition rates) while the overtemperature provided protection for the slower transients (low reactivity addition rates). Margin to DNB is maintained. The design basis for DNBR is described in Section 4.4.
Figures 15.4-5a and 15.4-5c show the minimum DNBR as a function of reactivity insertion rate for RCCA withdrawal incidents starting at 100, 60, and 10 percent power, respectively. In no case does the minimum DNBR exceed the acceptance limit. Figures 15.4-6a through 15.4-6c show the transient results of the RCS pressure analysis of the RWAP accident event. The limiting conditions are end of life, 10% rated thermal power and 41 pcm/sec reactivity addition rate. Peak pressure response is shown in Figure 15.4-6c with a peak pressure of 2734 psia which is less than 110% of the design pressure (2748.2 psia). Primary protection over the range of RCS pressure cases analyzed is pressurizer pressure, overtemperature , high neutron flux, and high neutron flux positive flux rate.
15.4-9 Rev. 25 WOLF CREEK Figures 15.4-7a through 15.4-7c show the transient results of the pressurizer fill analysis of the RWAP accident event. The limiting conditions are end of life, 10% rated thermal power and 8 pcm/sec reactivity addition rate. Peak pressurizer fill response is shown in Figure 15.4-7c with a peak pressurizer level of 97.6% which is less than 100% fill. Primary protection over the range of pressurizer fill cases analyzed is overtemperature , and high neutron flux. It is concluded the reactor coolant system pressure boundary is not threatened by this transient. Since the RCCA withdrawal at power incident is an overpower transient, the fuel temperatures rise during the transient until after reactor trip occurs. For
high reactivity insertion rates, the overpower transient is fast with respect
to the fuel rod thermal time constant, and the core heat flux lags behind the
neutron flux response. Due to this lag, the peak core heat flux does not exceed 118 percent of its nominal value (i.e., the high neutron flux trip
setpoint assumed in the analysis). Taking into account the effect of the RCCA
withdrawal on the axial core power distribution, the peak fuel temperature will
still remain below the fuel melting temperature.
For slow reactivity insertion rates, the core heat flux remains more nearly in
equilibrium with the neutron flux. The overpower transient is terminated by the overtemperature T reactor trip before a DNB condition is reached. The peak heat flux again is maintained below 118 percent of its nominal value. Taking into account the effect of the RCCA withdrawal on the axial core power
distribution, the peak clad centerline temperature will remain below the fuel
melting temperature.
The reactor is tripped sufficiently fast during the RCCA bank withdrawal at
power transient so that the ability of the primary coolant to remove heat from
the fuel rods is not reduced. Thus, the fuel cladding temperature does not
rise significantly above its initial value during the transient.
15.4-10 Rev. 25 WOLF CREEK The calculated sequence of events for this accident is shown on Table 15.4-1.
With the reactor tripped, the plant eventually returns to a stable condition.
The plant may subsequently be cooled down further by following normal plant
shutdown procedures.
15.4.2.3 Conclusions
The high neutron flux and overtemperature T trip channels provide adequate protection over the entire range of possible reactivity insertion rates, i.e., the minimum value of DNBR is always larger than the safety analysis limit.
15.4.3 ROD CLUSTER CONTROL ASSEMBLY MISOPERATION (System
Malfunction or Operator Error)
15.4.3.1 Identification of Causes and Accident Description Rod cluster control assembly (RCCA) misoperation accidents include:
- a. One or more dropped RCCAs within the same group, or a dropped RCCA bank
- b. Statically misaligned RCCA
- c. Withdrawal of a single RCCA
Each RCCA has a position indicator channel which displays the position of the
assembly. The displays of assembly positions are grouped for the operator's
convenience. Fully inserted assemblies are further indicated by a rod at
bottom signal, which actuates a local alarm and a control room annunciator.
Group demand position is also indicated. RCCAs are always moved in preselected banks, and the banks are always moved in
the same preselected sequence. Each bank of RCCAs is divided into groups of
four or five. The RCCAs comprising a group operate in parallel through
multiplexing thyristors. The groups in a bank move sequentially such that the
first group is always within one step of the second group in the bank. A
definite schedule of actuation (or deactuation of the stationary gripper, movable gripper, and lift coils of a mechanism) is required to withdraw the
RCCA attached to the mechanism. Since the stationary gripper, movable gripper, and lift coils associated with the four RCCAs of a rod group are driven in
parallel, any single failure which would cause rod withdrawal would affect a
minimum of one group. Mechanical failures are in the direction of insertion or
immobility.
The dropped RCCA assemblies, dropped RCCA assembly bank, and statically misaligned RCCA assembly events are classified as ANS Condition II incidents (incidents of moderate frequency), as defined in Section 15.0.1. The single
RCCA withdrawal incident is classified as an ANS Condition III event, as
discussed below.
15.4-11 Rev. 25 WOLF CREEK No single electrical or mechanical failure in the rod control system could
cause the accidental withdrawal of a single RCCA from the inserted bank at full
power operation. The operator could withdraw a single RCCA in the control bank
since this feature is necessary in order to retrieve an assembly should one be accidentally dropped. The event analyzed must result from multiple wiring
failures [probability for single random failure is on the order of 10 -4/year (refer to Section 7.7.2.2)] or multiple significant operator errors and
subsequent and repeated operator disregard of event indication. The
probability of such a combination of conditions is considered low. The limiting
consequences of such errors or failures may include slight fuel damage.
Thus, consistent with the philosophy and format of ANSI N18.2, the event is
classified as a Condition III event. By definition "Condition III occurrences
include incidents, any one of which may occur during the lifetime of a particular plant," and "shall not cause more than a small fraction of fuel elements in the reactor to be damaged . . ."
This classification is in accordance with GDC-25 which states, "The protection
system shall be designed to assure that specified acceptable fuel design limits
are not exceeded for any single malfunction of the reactivity control systems, such as accidental withdrawal (not ejection or dropout) of control rods ." (Emphasis has been added). It has been shown that single failures resulting in RCCA bank withdrawals do not violate specified fuel design limits. Moreover, no single malfunction can result in the withdrawal of a single RCCA. Thus, it
is concluded that the criterion established for the single rod withdrawal at power is appropriate and in accordance with GDC-25.
A dropped RCCA or RCCA bank is detected by:
- a. Sudden drop in the core power level as seen by the
nuclear instrumentation system
- b. Asymmetric power distribution as seen on out-of-core
neutron detectors or core exit thermocouples
- c. Rod at bottom signal
- d. Rod deviation alarm (control rods only)
- e. Rod position indication
Misaligned RCCAs are detected by:
- a. Asymmetric power distribution as seen on out-of-core
neutron detectors or core exit thermocouples
- b. Rod deviation alarm (control rods only)
- c. Rod position indication
15.4-12 Rev. 25 WOLF CREEK The resolution of the rod position indicator channel is +12 steps (+7.5 inches). Deviation of any RCCA from its group by twice this distance (+24
steps or +15.0 inches) will not cause power distributions worse than the design
limits. The deviation alarm (control rods only) alerts the operator to rod
deviation with respect to the group position in excess of 12 steps. If the rod deviation alarm is not operable, the operator is required to take action
required by the Technical Requirements Manual.
If one or more rod position indicator channels should be out of service, detailed operating instructions shall be followed to assure the alignment of
the nonindicated RCCAs. The operator is also required to take action, as
required by the Technical Specifications.
In the extremely unlikely event of simultaneous electrical failures which could
result in single RCCA withdrawal, rod deviation and rod control urgent failure would both be displayed on the plant annunciators, and the rod position indicators would indicate the relative positions of the assemblies in the bank.
The urgent failure alarm also inhibits automatic rod motion in the group in
which it occurs. Withdrawal of a single RCCA by operator action, whether
deliberate or by a combination of errors, would result in activation of the
same alarm and the same visual indications. Withdrawal of a single RCCA
results in both positive reactivity insertion tending to increase core power
and an increase in local power density in the core area associated with the
RCCA. Automatic protection for this event is provided by the overtemperature T reactor trip, although due to the increase in local power density it is not possible in all cases to provide assurance that the core safety limits will not be violated.
Major plant systems and equipment available for mitigation of transient and
accident conditions which may be required to function to mitigate the effects
of the various control rod misoperations and discussed in Section 15.0.8 and
listed in 15.0-6. The actual parameters assumed and results are given in the
respective section/subsection. Table 15.0-6 incorporates events shown in the
sequence diagram, Figures 15.0-17 & 18.
15.4.3.2 Analysis of Effects and Consequences 15.4.3.2.1 Dropped RCCAs, Dropped RCCA Bank, and Statically
Misaligned RCCA
Method of Analysis
- a. One or more dropped RCCAs from the same group or bank:
The purpose of this calculation is to demonstrate that, for all dropped RCCA
worths considered, the post-drop minimum DNBR will be greater than the design
limit. Credit is taken for high negative flux rate trip in that no combination
of dropped RCCAs is considered which has a worth greater than 400 pcm. For
evaluation of the dropped RCCA event, various combinations of dropped RCCAs (patterns) are considered. The initial conditions prior to RCCA drop are assumed to be: full power, RCCA control system on automatic, bank D inserted to its full-power limit, and all other RCCAs full out.
15.4-13 Rev. 25 WOLF CREEK Calculations are performed with the code DRPROD (Reference 15). Plant and
cycle specific values of several conditions are verified to be within
appropriate ranges for use of the Westinghouse generic systems transient
analysis. Generic systems transient statepoints programmed into the DRPROD code cover the ranges of reactivity change mechanisms (RCCA drop, control bank
withdrawal, MTC) such that all appropriate combinations of these parameters
throughout cycle life are considered.
Maximum reactivity insertion due to bank D withdrawal from HFP RIL is
determined at 150 MWD/T and EOL (HFP equilibrium xenon) by ANC calculation (Reference 16). DRPROD code uses these values and linear interpolation to
determine maximum reactivity insertion due to bank D withdrawal at burnups
between 150 MWD/T and EOL. HFP MTC values are determined at BOL, EOL, and at
the burnup for which MTC is at a maximum (least negative) for the cycle; these are determined by ANC calculation. These reactivity and MTC values are input to DRPROD. Other plant-specific and cycle-specific input to DRPROD
calculations as outlined in Reference 15 includes HFP moderator inlet temperature and core average moderator temperature, nuclear uncertainty on F, dropped rod limit lines and design F. Dropped rod limit lines show, as a function of RCS pressure and inlet temperature, the power at which minimum DNBR equals the design limit.
- b. Statically misaligned RCCA:
Cases of fully misaligned RCCAs are covered by the analyses described above in Part a. Consequences of cases of partially misaligned RCCAs are bounded by the
analyses for Part a.
Results
- a. One or more dropped RCCAs from the same group or bank:
Due to negative flux rate trip protection, the minimum dropped RCCA worth which will cause reactor trip is 400 pcm (Reference 15). Dropped RCCAs with worths
greater than this value will result in reactor trip and need not be included in
the power distribution analysis.
Output from DRPROD includes a table of F versus burnup; these F are the values calculated to be necessary as pre-drop F if the post-drop transient is to produce a minimum DNBR which is less than the design limit. DRPROD code is run and output is checked to confirm that, for each of the analysized patterns of dropped RCCAs, the precondition F which would be required in order for the dropped RCCA event with bank D withdrawal to violate minimum DNBR, is greater than the design limit. This demonstrates that the DNB design basis is not
violated in any dropped RCCA event since necessary preconditions would not
exist. Dropped RCCA transient analysis parameters are presented in Figures 15.4-10 and
15.4-11a.
- b. Statically misaligned RCCA
The most severe misalignment situations with respect to DNBR at significant
power levels arise from cases in which one RCCA is fully inserted or where bank
D is fully inserted with one RCCA fully withdrawn. Multiple independent
alarms, including a bank insertion limit alarm, alert the operator well before the postulated conditions are approached. The bank can be inserted to its insertion limit with any one assembly fully withdrawn without the DNBR falling
below the limit value.
15.4-14 Rev. 25 WOLF CREEK The insertion limits in the Core Operating Limits Report (COLR) may vary from
time to time, depending on a number of limiting criteria. The full power
insertion limits on control bank D must be chosen to be above that position
which meets minimum DNBR and peaking factors. The full power insertion limit is usually dictated by other criteria. Detailed results will vary from cycle to
cycle, depending on fuel arrangements.
For this RCCA misalignment with bank D inserted to its full power insertion
limit and one RCCA fully withdrawn, DNBR does not fall below the limit value.
This case is analyzed assuming the initial reactor power, pressure, and RCS
temperature are at their nominal values including uncertainties (as given in
Subsection 15.0.3.2), but with the increased radial peaking factor associated
with the misaligned RCCA.
For RCCA misalignments with one RCCA fully inserted, the DNBR does not fall below the limit value. This case is analyzed assuming that the initial reactor
power, pressure, and RCS temperatures are at their nominal values, including
uncertainties, but with the increased radial peaking factor associated with the
misaligned RCCA.
DNB does not occur for the RCCA misalignment incident, and thus, the ability of
the primary coolant to remove heat from the fuel is not reduced. The peak fuel
temperature corresponds to a linear heat generation rate based on the radial
peaking factor penalty associated with the misaligned RCCA and the design axial
power distribution. The resulting linear heat generation is well below that
which would cause fuel melting.
Following the identification of an RCCA group misalignment condition by the
operator, the operator is required to take action as required by the plant Technical Specifications and operating instructions.
15.4.3.2.2 Single RCCA Withdrawal
Method of Analysis Power distributions within the core are calculated using the computer code ANC.
Analysis of the redistribution of power which occurs with the withdrawal of a
single RCCA determines the fraction of pins for which DNBR falls below the limit value. The case of the worst rod withdrawn from bank D inserted at the
insertion limit, with the reactor initially at full power, is analyzed. The
purpose of this calculation is to confirm that the number of fuel rods that go
through DNB is less than the safety analysis limit of 5%.
The calculations is performed at the burnup step which has the highest peak F. Power distributions are generated for all combinations of bank D inserted less one bank D RCCA out using xenon reconstruction to skew the axial offset to upper allowable limit. This determines the bank D RCCA which produces the
highest peak assembly powers when stuck out of the core.
15.4-15 Rev. 25 WOLF CREEK Results ANC analysis is done at the burnup step and with the stuck bank D RCCA as mentioned above. If the highest peak F from ANC results, multiplied by a calculational uncertainly factor of 1.08, is less than the F design limit, then all rods meet the DNB criteria. If this is not the case, ANC analysis is repeated with the generation of a fuel census including the uncertainly factor of 1.08. From this census the percentage of fuel rods with F exceeding the design limit is determined.
15.4.3.3 Conclusions
For cases of dropped RCCAs or dropped banks for which the reactor is tripped by
the power range negative neutron flux rate trip, there is no reduction in the
margin to core thermal limits, and consequently, the DNB design basis is met. For all cases that do not result in reactor trip, it is shown that the DNBR
remains greater than the limit value and, therefore, the DNB design is met.
For all cases of any RCCA fully inserted, or bank D inserted to its rod
insertion limits with any single RCCA in that bank fully withdrawn (static
misalignment), the DNBR remains greater than the limit value.
For the case of the accidental withdrawal of a single RCCA, with the reactor in
the automatic or manual control mode and initially operating at full power with
bank D at the insertion limit, an upper bound of the number of fuel rods experiencing DNB is 5 percent of the total fuel rods in the core.
15.4.4 STARTUP OF AN INACTIVE REACTOR COOLANT PUMP AT AN
INCORRECT TEMPERATURE
15.4.4.1 Identification of Causes and Accident Description If the plant is operating with one pump out of service, there is reverse flow
through the inactive loop due to the pressure difference across the reactor
vessel. The cold leg temperature in an inactive loop is identical to the cold leg temperature of the active loops (the reactor core inlet temperature). If
the reactor is operated at power, and assuming the secondary side of the steam
generator in the inactive loop is not isolated, there is a temperature drop
across the steam generator in the inactive loop and, with the reverse flow, the
hot leg temperature of the inactive loop is lower than the reactor core inlet
temperature.
Administrative procedures require that the unit be brought to a load of less
than 10 percent of full power prior to starting the pump in an inactive loop in
order to bring the inactive loop hot leg temperature closer to the core inlet temperature. Starting of an idle reactor coolant pump without bringing the inactive loop hot leg temperature close to the core inlet temperature would
result in the injection of cold water into the core, which would cause a
reactivity insertion and subsequent power increase.
This event is classified as an ANS Condition II incident (a fault of moderate
frequency) as defined in Section 15.0.1.
15.4-16 Rev. 25 WOLF CREEK Should the startup of an inactive reactor coolant pump accidentally occur, the
ensuing transient is terminated automatically by a reactor trip on low coolant
loop flow when the power range neutron flux (two out of four channels) exceeds
the P-8 setpoint, which has been previously reset for three-loop operation.
15.4.4.2 Analysis of Effects and Consequences Method of Analysis
This transient is analyzed by using three digital computer codes. The LOFTRAN
code (Ref. 3) is used to calculate the loop and core flow, nuclear power and
core pressure, and temperature transients following the startup of an idle pump. VIPRE-01 (Ref 14) is used to evaluate the core thermal limits to
determine DNBR. LOFTRAN generated state points are used as VIPRE-01 boundary
conditions to perform the DNB analysis.
Plant characteristics and initial conditions are discussed in Section 15.0.3.
To obtain conservative results for the startup of an inactive pump accident, the following assumptions are made:
- a. Initial conditions of maximum core power and reactor
coolant average temperatures and minimum reactor coolant pressure resulting in minimum initial margin to DNB. These values are consistent with maximum steady state
power level allowed with three loops in operation. The
high initial power gives the greatest temperature
difference between the core inlet temperature and the
inactive loop hot leg temperature.
- b. Following initiation of startup of the idle pump, the
inactive loop flow reverses and accelerates to its
nominal full flow value in approximately 27 seconds.
- c. A conservatively large negative moderator temperature
coefficient.
- d. A least negative Doppler only power coefficient (see Figure 15.0-2).
- e. The initial reactor coolant loop flows are at the
appropriate values for one pump out of service.
- f. The reactor trip is assumed to occur on low coolant loop
flow when the power range neutron flux exceeds the P-8
setpoint. The P-8 setpoint is conservatively assumed to
be 84 percent of rated power which corresponds to the
nominal setpoint plus 9 percent for nuclear
instrumentation errors.
Major plant systems and equipment available for mitigation of transient and
accident conditions are discussed in Section 15.0-8 and listed in Table 15.0-6.
The actual parameters assumed and results are given in the respective
section/subsection. Table 15.0-6 incorporates events shown in the sequence
diagram, Figure 15.0-19.
15.4-17 Rev. 25 WOLF CREEK Results The results following the startup of an idle pump with the above listed
assumptions are shown in Figures 15.4-12 through 15.4-16. As shown in these
curves, during the first part of the transient, the increase in core flow with cooler water results in an increase in nuclear power and a decrease in core
average temperature. The minimum DNBR during the transient is considerably
greater than the safety analysis limit. See Section 4.4 for a description of
the DNBR design basis.
Reactivity addition for the inactive loop startup accident is due to the
decrease in core water temperature. During the transient, this decrease is due
both to the increase in reactor coolant flow and, as the inactive loop flow
reverses, to the colder water entering the core from the hot leg side (colder
temperature side prior to the start of the transient) of the steam generator in the inactive loop. Thus, the reactivity insertion rate for this transient changes with time. The resultant core nuclear power transient, computed with
consideration of both moderator and Doppler reactivity feedback effects, is
shown on Figure 15.4-12.
The calculated sequence of events for this accident is shown on Table 15.4-1.
The transient results illustrated in Figures 15.4-12 through 15.4-16 indicate
that a stabilized plant condition, with the reactor tripped, is rapidly
attained. Plant cooldown may subsequently be achieved by following normal
shutdown procedures.
15.4.4.3 Conclusions The transient results show that the core is not adversely affected. There is a
considerable margin to the limiting DNBR; thus, the DNB design basis, as
described in Section 4.4, is met.
15.4.5 A MALFUNCTION OR FAILURE OF THE FLOW CONTROLLER IN A BWR
LOOP THAT RESULTS IN AN INCREASED REACTOR COOLANT
FLOW RATE
This section is not applicable to Wolf Creek.
15.4.6 CHEMICAL AND VOLUME CONTROL SYSTEM MALFUNCTION THAT
RESULTS IN A DECREASE IN THE BORON CONCENTRATION IN
THE REACTOR COOLANT 15.4.6.1 Identification of Causes and Accident Description One of the two principal means of positive reactivity insertion to the core is
the addition of unborated, primary grade water from the demineralized and
reactor makeup water system (RMWS) into the
RCS through the reactor makeup portion of the chemical and volume control
system (CVCS). Boron dilution with these systems is a manually initiated
operation under strict administrative controls requiring close operator
surveillance with procedures limiting the rate and duration of the dilution.
A boric acid blend system is available to allow the operator to match the
makeup's boron concentration to that of the RCS during normal charging.
15.4-18 Rev. 25 WOLF CREEK The means of causing an inadvertent boron dilution are the opening of the
primary water makeup control valve and failure of the blend system, either by
controller or mechanical failure. The CVCS and RMWS are designed to limit, even
under various postulated failure modes, the potential rate of dilution to
values which, with indication by alarms and instrumentation, will allow
sufficient time for automatic or operator response (depending on the mode of
operation) to terminate the dilution. An inadvertent dilution from the RMWS may
be terminated by closing the primary water makeup control valve. All expected
sources of dilution may be terminated by closing isolation valves in the CVCS, BG-LCV-112B and C. The lost shutdown margin (SDM) may be regained by the
opening of isolation valves to the RWST, BN-LCV-112D and E, thus allowing the
addition of borated water to the RCS.
Generally, to dilute, the operator must perform two distinct actions:
- a. Switch control of the makeup from the automatic makeup
mode to the dilute mode
- b. Momentarily place handswitch BGHS0026, RCS M/U CTRL, to RUN
Failure to carry out either of the above actions prevents initiation of
dilution. Also, during normal operation the operator may add borated water to
the RCS by blending boric acid from the boric acid storage tanks with primary
grade water. This requires the operator to determine the concentration of the
addition and to set the blended flow rate and the boric acid flow rate. The
makeup controller will then limit the sum of the boric acid flow rate and
primary grade water flow rate to the blended flow rate, i.e., the controller
determines the primary grade water flow rate after the start button is
depressed.
The status of the RCS makeup is continuously available to the operator by:
- a. Indication of the boric acid and blended flow rates
- b. CVCS and RMWS pump status lights
- c. Deviation alarms, if the boric acid or blended flow
rates deviate by more than 10 percent from the preset
values
- d. High charging flow rate alarm
- e. Volume control tank high and high-high water level and
high pressure alarms
- f. Letdown divert valve position alarm
- g. Source range neutron flux - when reactor is subcritical
- 1. High flux at shutdown alarm
- 2. Indicated source range neutron flux count rates
- 3. Audible source range neutron flux count rate
- 4. Source range neutron flux - doubling alarm
15.4-19 Rev. 28 WOLF CREEK
- h. When the reactor is critical
- 1. Axial flux difference alarm (reactor power
>=50 percent RTP)
- 2. Control rod insertion limit low and low-low alarms
- 3. Overtemperature T alarm (at power)
- 4. Overtemperature T turbine runback (at power)
- 5. Overtemperature T reactor trip
- 6. Power range neutron flux - high, both high and low
setpoint reactor trips
This event is classified as an ANS Condition II incident (a fault of moderate
frequency) as defined in Section 15.0.1.
Major plant systems and equipment available for mitigation of transient and accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6. The actual parameters assumed and results are given in the respective section/subsection. Table 15.0-6 incorporates events shown in the sequence diagram, Figure 15.0-20. 15.4.6.2 Analysis of Effects and Consequences
To cover all phases of plant operation, boron dilution during Cold Shutdown, Hot Shutdown, Hot Standby, Start-up, and Power modes of operation is considered
in this analysis. Conservative values for necessary parameters were used, i.e., high RCS critical boron concentrations, high boron worths, minimum
shutdown margins, and lower than actual RCS volumes. These assumptions result
in conservative determinations of the time available for operator or system
response after detection of a dilution transient in progress.
Dilution During Refueling An uncontrolled boron dilution transient cannot occur during this mode of
operation. Inadvertent dilution is prevented by administrative controls which
isolate the RCS from the potential source of unborated water. Valves V-178 and V-601 (or V-602) in the CVCS will be locked closed during refueling operations.
These valves block all flow paths that could allow unborated makeup water to
reach the RCS. Any makeup which is required during refueling will be borated
water supplied from the RWST by the RHR pumps or the CCPs if using the CCP to
flood up the Refueling Pool.
15.4-20 Rev. 25 WOLF CREEK Dilution During Cold Shutdown, Hot Shutdown and Hot Standby
The Technical Specifications require the reactor to be shutdown to a SDM value
as specified in the COLR when the unit is operating in Mode 5, Cold Shutdown.
When in Modes 4 or 3, (Hot Shutdown or Hot Standby), the Technical Specifications require the plant to be shutdown to a SDM value as specified in
the COLR. The following conditions are assumed for the analysis of the
inadvertent boron dilution event while in these operating modes:
- a. An assumed dilution flow rate of 157.5 gpm is used. This value corresponds to the high charging flow rate alarm plus a 5%
allowance for uncertainties.
- b. A minimum RCS water volume of 8725 ft 3 is assumed. This volume is a conservative estimate of the active volume of the RCS when at least one reactor coolant pump is in operation.
- c. If no reactor coolant pump is in operation, all dilution sources are isolated or under administrative control.
Dilution During Start-up In this mode, the plant is being taken from one long-term mode of operation, Hot Standby, to another, Power. The plant is maintained in the Start-up mode
only for the purpose of start-up testing at the beginning of each cycle. During this mode of operation, the plant is in manual control, i.e., T avg/rod control is in manual. All normal actions required to change power level, either up or down, require operator initiation. The COLR and Technical Specifications require an available trip reactivity of 1.3 percent K/K (in MODE 2 with K eff < 1.0) and four reactor coolant pumps operating. Other conditions assumed are:
- a. Dilution flow is the maximum capacity of two centrifugal charging pumps with the RCS at 2250 psia (approximately 245 gpm).
- b. A minimum RCS water volume of 9965 ft
- 3. This is a conservative estimate of the active RCS volume, minus the pressurizer volume.
Dilution During Full Power Operation The plant may be operated at power two ways: automatic T avg/rod control and under operator control. The COLR specifies an available trip reactivity of 1.3 percent K/K and four reactor coolant pumps operating. With the plant at power and the RCS at pressure, the dilution rate is limited by the capacity of the centrifugal charging pumps (analysis is performed assuming two charging pumps
are in operation even though normal operation is with one pump). Conditions
assumed for this mode are:
15.4-21 Rev. 25 WOLF CREEK
- a. Dilution flow from two centrifugal charging pumps is at the maximum at an RCS pressure of 2250 psia (approximately 245 gpm) when the reactor is in manual control. When in automatic control, the dilution flow is the maximum letdown flow (approximately 120 gpm).
- b. A minimum RCS water volume of 9965 ft
- 3. This is a conservative estimate of the active RCS volume, minus the pressurizer volume.
15.4.6.3 Conclusions Dilution During Refueling
Dilution during this mode has been precluded through administrative control of
valves in the possible dilution flow paths (see Section 15.4.6.2).
Dilution During Cold Shutdown, Hot Shutdown or Hot Standby In Modes 3, 4 or 5, the reactor operators are relied upon to detect and recover
from a inadvertent boron dilution event. Numerous alarms from the CVCS and
RMWS and in the Nuclear Instrumentation System are available to provide assistance to the reactor operator in the detection of an inadvertent boron
dilution event. In the analyses of the event initiated from Modes 3, 4 or 5, the VCT high water level alarm (at 70% span) is credited as the initial alarm.
The time required to perform the VCT/RWST valve swap-over and to purge the
charging lines of dilute water are included in the calculation of the time
available to the reactor operators to initiate corrective actions. In Modes 3, 4 and 5, analyses have demonstrated that the reactor operators have at least 15
minutes in which to initiate actions to terminate the dilution and initiate
boration of the RCS.
There may exist other dilution events not obviously bounded by the analysis scenario described above. For example, during small dilution flow rate
situations, the time required to fill the VCT to the high VCT water level
setpoint may exceed the time required to dilute the RCS to the critical
condition. However, the time intervals involved in this case are relatively
long and alternate alarms, such as the concentrated boric acid flow and total
makeup flow deviation alarms, would alert the reactor operator to a potential
inadvertent boron dilution. For these relatively slow transients, an alternate
event acceptance criterion is applied. This criterion requires that the time
between the start of the event and the complete loss of shutdown margin (inadvertent criticality) be at least 30 minutes.
Dilution During Startup This mode of operation is a transitory mode to go to power and is the
operational mode in which the operator intentionally dilutes and withdraws
control rods to take the plant critical. During this mode, the reactor is in manual rod control with the operator required to maintain a very high awareness
of the plant status. For a normal approach to criticality, the operator must
manually initiate a limited dilution and subsequently manually withdraw the
control rods, a process that takes several hours. The plant Technical
Specifications require that the operator determine the estimated critical
15.4-22 Rev. 25 WOLF CREEK position of the control rods prior to approaching criticality thus assuring
that the reactor does not go critical with the control rods below the insertion
limits. Once critical, the power escalation must be sufficiently slow to allow
the operator to manually block the Source Range reactor trip after receiving P-6 from the Intermediate Range. Too fast a power escalation (due to an
unknown dilution) would result in reaching P-6 unexpectedly, leaving
insufficient time to manually block the Source Range reactor trip. Failure to
perform this manual action results in a reactor trip and immediate shutdown of
the reactor.
For Mode 2 - Startup, the reactor is assumed to trip when the flux level
reaches the source range high flux trip setpoint. In the event of an
inadvertent dilution, no credit is taken for operator action blocking the
source range trip (permissive P-6). This reactor trip also functions as an alarm indicating a boron dilution transient is under way, as the control rods are not moving. The control rods are assumed to be at the insertion limits, minimizing the available shutdown margin; it is assumed that the RCS boron
concentration at the time of reactor trip corresponds to the predicted critical
boron concentration for rods at the insertion limits. Note: Due to the
selection of boron concentration assumptions, the time available from the alarm
is calculated to be identical to the total time from event initiation to loss
of shutdown margin, i.e., the time of alarm will coincide with the analysis
initial condition assumption. After reactor trip there is at least 15 minutes
for operator action prior to return to criticality. The required operator
action is the opening of valves BN-LCV-112D and E to initiate boration and the
closing of valves BG-LCV-112B and C to terminate dilution.
Dilution During Full Power Operation With the reactor under manual rod control and no operator action taken to
terminate the transient, the power and temperature rise will cause the reactor to reach the Overtemperature T trip setpoint resulting in a reactor trip. After reactor trip there is at least 60 minutes for operator action prior to return to criticality. The required operator action is the opening of valves
BN-LCV-112D and E and the closing of valves BG-LCV-112B and C. The boron
dilution transient in this case is essentially equivalent to an uncontrolled
rod withdraw at power. A reactor trip occurs when either the Hi Neutron Flux or the Overtemperature T setpoint is reached. The maximum reactivity insertion rate for a boron dilution transient is conservatively estimated to be within the range of insertion rates analyzed for uncontrolled rod withdraw at
power. It should be noted that prior to reaching the Overtemperature T reactor trip the operator will have received an alarm on Overtemperature T and an Overtemperature T turbine runback. With the reactor in automatic rod control, the pressurizer level controller will limit the dilution flow rate to the maximum letdown rate, approximately 120 gpm. If a dilution rate in excess of
the letdown rate is present, the pressurizer level controller will throttle
charging flow down to match the letdown rate.
15.4-23 Rev. 25 WOLF CREEK Thus, with the reactor in automatic rod control, a boron dilution will result
in a power and temperature increase such that the rod controller will attempt
to compensate by slow insertion of the control rods. This action by the
controller will result in at least three alarms to the operator:
- a. rod insertion limit - low level alarm.
- b. rod insertion limit - low-low level alarm if insertion continued after (a) above, and
- c. axial flux difference alarm (T outside of the target band).
Given the many alarms, indications, and the inherent slow process of dilution
at power, the operator has sufficient time for action. For example, the
operator has at least 60 minutes from the rod insertion limit low-low alarm
until shutdown margin is lost at beginning-of-life. The time would be
significantly longer at end-of-life, due to the low initial boron
concentration, when shutdown margin is a concern.
The above results demonstrate that in all modes of operation an inadvertent
boron dilution is precluded, or sufficient time is available for operator
action to terminate the transient. Following termination of the dilution flow
and initiation of boration, the reactor is in a stable condition with the
operator regaining the required shutdown margin.
15.4.7 INADVERTENT LOADING AND OPERATION OF A FUEL ASSEMBLY
IN IMPROPER POSITION
15.4.7.1 Identification of Causes and Accident Description Fuel and core loading errors that can arise from the inadvertent loading of one
or more fuel assemblies into improper positions, loading a fuel rod during
manufacture with one or more pellets of the wrong enrichment, or the loading of a full fuel assembly during manufacture with pellets of the wrong enrichment
will lead to increased heat fluxes if the error results in placing fuel in core
positions calling for fuel of lesser enrichment. Also included among possible
core loading errors is the inadvertent loading of one or more fuel assemblies
requiring burnable poison rods into a new core without burnable poison rods.
Any error in enrichment, beyond the normal manufacturing tolerances, can cause
power shapes which are more peaked than those calculated with the correct
enrichments. There is a 5-percent uncertainty margin included in the design
value of power peaking factor assumed in the analysis of Condition I and Condition II transients. The in-core system of moveable flux detectors, which is used to verify power shapes at the start of life, is capable of revealing
any assembly enrichment error or loading error which causes power shapes to be
peaked in excess of the design value.
To reduce the probability of core loading errors, each fuel assembly is marked
with an dentification number and loaded in accordance with a core loading
diagram. After the core is completely loaded, the identification number and
position of each fuel assembly is recorded and compared to the design pattern.
15.4-24 Rev. 25 WOLF CREEK The power distortion due to any combination of misplaced fuel assemblies would significantly raise peaking factors and would be readily observable with in-
core flux monitors. In addition to the flux monitors, thermocouples are located at the outlet of about one-quarter of the fuel assemblies in the core. There is a high probability that these thermocouples would also indicate any
abnormally high coolant enthalpy rise. In-core flux measurements are taken
during the startup subsequent to every refueling operation. This event is classified as an ANS Condition III incident (an infrequent fault), as defined in Section 15.0.1. 15.4.7.2 Analysis of Effects and Consequences Method of Analysis Steady state power distributions in the x-y plane of the initial core were calculated using the TURTLE code (Ref. 4) based on macroscopic cross sections
calculated by the LEOPARD code (Ref. 5). A discrete representation was used
wherein each individual fuel rod was described by a mesh interval. Current
methodology applies the ANC code (Ref 16) to calculate power distributions; however, the TURTLE/LEOPARD analysis of the initial core remains valid. For each core loading error case analyzed, for the initial core, the percent deviations from detector readings for a normally loaded core are shown at all
in-core detector locations (see Figures 15.4-17 to 15.4-21, inclusive). Results, Initial Core The enrichments for cycle 1 at Wolf Creek were 2.10 (Region 1), 2.60 (Region 2), and 3.10 (Region 3) weight percent. The following core loading error cases
were analyzed: Case A: Case in which a Region 1 assembly is interchanged with a Region 3 assembly. The particular case considered was the interchange to two adjacent assemblies near the periphery of the core (see Figure 15.4-17). Case B: Case in which a Region 1 assembly is interchanged with a neighboring Region 2 fuel assembly. Two analyses have been performed for this case (see Figures
15.4-18 and 15.4-19). In Case B-1, the interchange is assumed to take place with the burnable poison rods transferred with the Region 2 assembly mistakenly loaded into Region 1. In Case B-2, the interchange is assumed to take place closer to core center and with burnable poison rods located in the correct Region 2 position, but in a
Region 1 assembly mistakenly loaded in the Region 2 position. Case C: Enrichment error: Case in which a Region 2 fuel assembly is loaded in the core central position (see Figure 15.4-20). 15.4-25 Rev. 12 WOLF CREEK Case D: Case in which a Region 2 fuel assembly instead of a Region 1 assembly is loaded near the core periphery (see Figure 15.4-21). 15.4.7.3 Conclusions Fuel assembly enrichment errors are prevented by administrative procedures implemented in fabrication.
In the event that a single pin or pellet has a higher enrichment than the nominal value, the consequences in terms of reduced DNBR and increased fuel and
clad temperatures will be limited to the incorrectly loaded pin or pins and
perhaps the immediately adjacent pins. Fuel assembly loading errors are prevented by administrative procedures implemented during core loading. In the unlikely event that a loading error occurs, the resulting power distribution effects will either be readily detected by the in-core moveable detector system or will cause a sufficiently small perturbation to be acceptable within the uncertainties allowed between
nominal and design power shapes. 15.4.8 SPECTRUM OF ROD CLUSTER CONTROL ASSEMBLY EJECTION ACCIDENTS 15.4.8.1 Identification of Causes and Accident Description This accident is defined as the mechanical failure of a control rod mechanism pressure housing, resulting in the ejection of an RCCA and drive shaft. The
consequence of this mechanical failure is a rapid positive reactivity insertion and system depressurization together with an adverse core power distribution, possibly leading to localized fuel rod damage. 15.4.8.1.1 Design Precautions and Protection
Certain features in the WCGS pressurized water reactor are intended to preclude the possibility of a rod ejection accident, or to limit the consequences if the
accident were to occur. These include a sound, conservative, mechanical design of the rod housings, together with a thorough quality control (testing) program during assembly, and a nuclear design which lessens the potential ejection
worth of RCCAs and minimizes the number of assemblies inserted at high power
levels.Mechanical Design The mechanical design is discussed in Section 4.6. Mechanical design and quality control procedures intended to preclude the possibility of an RCCA
drive mechanism housing failure are listed below: 15.4-26 Rev. 11 WOLF CREEK
- a. Each control rod drive mechanism housing is completely assembled and shop tested at 4,100 psi.
- b. The mechanism housings are individually hydrotested after they are attached to the head adapters in the reactor vessel head and checked during the hydrotest of the completed RCS.
- c. Stress levels in the mechanism are not affected by anticipated system transients at power, or by the
thermal movement of the coolant loops. Moments induced
by the design earthquake can be accepted within the
allowable primary working stress range specified by the
ASME Code, Section III, for Class 1 components.
- d. The latch mechanism housing and rode travel housing are each a single length of forged Type 304 stainless steel.
This material exhibits excellent notch toughness at all
temperatures which are encountered. A significant margin of strength in the elastic range, together with the large energy absorption capability in the plastic range, gives additional assurance
that gross failure of the housing will not occur. The joints between the latch
mechanism housing and head adapter, and between the latch mechanism housing and
rod travel housing, are threaded joints reinforced by canopy-type rod welds which are subject to periodic inspections. Nuclear Design Even if a rupture of an RCCA drive mechanism housing is postulated, the operation utilizing chemical shim is such that the severity of an ejected RCCA
is inherently limited. In general, the reactor is operated with the RCCAs
inserted only far enough to permit load follow. Reactivity changes caused by
core depletion and xenon transients are compensated for by boron changes.
Further, the location and grouping of control RCCA banks are selected during
the nuclear design to lessen the severity of an RCCA ejection accident.
Therefore, should an RCCA be ejected from its normal position during full power
operation, only a minor reactivity excursion, at worst, could be expected to occur.However, it may be occasionally desirable to operate with larger-than-normal insertions. For this reason, a rod insertion limit is defined as a function of power level. Operation with the RCCAs above this limit guarantees adequate shutdown capability and acceptable power distribution. The position of all RCCAs is continuously indicated in the control room. An alarm will occur if a bank of RCCAs approaches its insertion limit or if one RCCA deviates from its bank. Operating instructions require boration at a low level alarm and shutdown margin verification or boration at the low-low alarm. 15.4-27 Rev. 22 WOLF CREEK Reactor Protection The reactor protection in the event of a rod ejection accident has been described in Reference 6. The protection for this accident is provided by high neutron flux trip (high and low setting) and high rate of neutron flux increase trip. These protection functions are described in detail in Section 7.2. Effects on Adjacent Housings Disregarding the remote possibility of the occurrence of an RCCA mechanism housing failure, investigations have shown that failure of a housing due to
either longitudinal or circumferential cracking would not cause damage to
adjacent housings. The control rod drive mechanism is described in Section
3.9(N).4.Effects of Rod Travel Housing Longitudinal Failures If a longitudinal failure of the rod travel housing should occur, the region of the position indicator assembly opposite the break would be stressed by the
reactor coolant pressure of 2,250 psia. The most probable leakage path would
be provided by the radial deformation of the position indicator coil assembly, resulting in the growth of axial flow passages between the rod travel housing and the hollow tube along which the coil assemblies are mounted. If a failure of the position indicator coil assembly should occur, the resulting free radial jet from the failed housing could cause it to bend and
contact adjacent rod housings. If the adjacent housings were on the periphery, they might bend outward from their bases. The housing material is quite
ductile; plastic hinging without cracking would be expected. Housings adjacent
to a failed housing, in locations other than the periphery, would not be bent
because of the rigidity of multiple adjacent housings. Effect of Rod Travel Housing Circumferential Failures If circumferential failure of a rod travel housing should occur, the separated section of the housing would be ejected vertically because the driving force is
vertical and the position indicator coil assembly and the drive shaft would
tend to guide the separated section upwards during its travel. Travel is
limited by the missile shield, thereby limiting the projectile acceleration.
When the projectile reached the missile shield, it would dissipate its kinetic energy without penetrating the shield. The water jet from the break would continue to push the separated section against the missile shield. If the separated section of the rod travel housing were short enough to clear the break when fully ejected, it would rebound after impact with the missile
shield. The top end plates of the position indicator coil assemblies would
prevent the separated section from directly hitting the rod travel housing of a
second drive mechanism. Even if a direct hit by the rebounding separated
section were to occur, the low kinetic energy of the rebounding projectile
would not be expected to cause significant damage (sufficient to cause failure of an adjacent housing). 15.4-28 Rev. 19 WOLF CREEK Possible Consequences From the above discussion, the probability of damage to an adjacent housing must be considered remote. However, even if damage is postulated, it would not
be expected to lead to a more severe transient since RCCAs are inserted in the
core in symmetric patterns, and control rods immediately adjacent to worst
ejected rods are not in the core when the reactor is critical. Damage to an adjacent housing could, at worst, cause that RCCA not to fall on receiving a
trip signal; however, this is already taken into account in the analysis by
assuming a stuck rod adjacent to the ejected rod. Summary The considerations given above lead to the conclusion that failure of a control rod housing, due either to longitudinal or circumferential cracking, would not cause damage to adjacent housings that would increase severity of the initial accident.15.4.8.1.2 Limiting Criteria This event is classified as an ANS Condition IV incident. See Section 15.0.1 for a discussion of ANS classifications. Due to the extremely low probability
of an RCCA ejection accident, some fuel damage would be considered an
acceptable consequence. Comprehensive studies of the threshold of fuel failure and of the threshold of significant conversion of the fuel thermal energy to mechanical energy have
been carried out as part of the SPERT project by the Idaho Nuclear Corporation (Ref. 7). Extensive tests of UO 2 zirconium clad fuel rods representative of those in pressurized water reactor type cores have demonstrated failure thresholds in the range of 240 to 257 cal/gm. However, other rods of a slightly different design have exhibited failures as low as 225 cal/gm. These results differ
significantly from the TREAT (Ref. 8) results, which indicated a failure threshold of 280 cal/gm. Limited results have indicated that this threshold decreases by about 10 percent with fuel burnup. The clad failure mechanism appears to be melting for
zero burnup rods and brittle fracture for irradiated rods. Also important is
the conversion ratio of thermal to mechanical energy. This ratio becomes
marginally detectable above 300 cal/gm for unirradiated rods and 200 cal/gm for
irradiated rods; catastrophic failure (large fuel dispersal, large pressure
rise), even for irradiated rods, did not occur below 300 cal/gm. In view of the above experimental results, criteria are applied to ensure that there is little or no possibility of fuel dispersal in the coolant, gross lattice distortion, or severe shock waves. These criteria are (Ref. 12): a. Average fuel pellet enthalpy at the hot spot is below 225 cal/gm for unirradiated fuel and 200 cal/gm for irradiated fuel. b. Peak reactor coolant pressure is less than that which could cause stresses to exceed the faulted condition stress limits. c. Fuel melting is limited to less than 10 percent of the fuel volume at the hot spot even if the average fuel pellet enthalpy is below the limits of criterion a
above. d. Average clad temperature at the hot spot is below the temperature at which clad embrittlement may be expected (3000°F). 15.4-29 Rev. 13 WOLF CREEK 15.4.8.2 Analysis of Effects and Consequences 15.4.8.2.1 Method of Analysis The calculation of the RCCA ejection transient is performed in two stages, first an average core channel calculation and then a hot region calculation.
The average core calculation is performed, using spatial neutron kinetics
methods, to determine the average power generation with time, including the
various total core feedback effects, i.e., Doppler reactivity and moderator
reactivity. Enthalpy and temperature transients at the hot spot are then
determined by multiplying the average core energy generation by the hot channel factor and performing a fuel rod transient heat transfer calculation. The power distribution calculated without feedback is conservatively assumed to persist throughout the transient. A detailed discussion of the method of analysis can be found in Reference 6 and Reference 12. Average Core Analysis The spatial kinetics computer code, TWINKLE (Ref. 1), is used for the average core transient analysis. This code uses cross sections generated by LEOPARD (Ref. 5) to solve the two group neutron diffusion theory kinetic equation in
one, two, or three spatial dimensions (rectangular coordinates) for six delayed neutron groups and up to 2,000 spatial points. The computer code includes a detailed multiregion, transient fuel-clad coolant heat transfer model for
calculation of pointwise Doppler and moderator feedback effects. In this analysis, the code is used as a one-dimensional axial kinetics code, since it
allows a more realistic representation of the spatial effects of axial
moderator feedback and RCCA movement. However, since the radial dimension is missing, it is still necessary to employ very conservative methods (described below) of calculating the ejected rod worth and hot channel factor. Further
description of TWINKLE appears in Section 15.0.11. Hot Spot Analysis In the hot spot analysis, the initial heat flux is equal to the nominal value times the design hot channel factor. During the transient, the heat flux hot
channel factor is linearly increased to the transient value in 0.1 second, the time for full ejection of the rod. Therefore, the assumption is made that the hot spot before and after ejection is coincident. This is very conservative since the peak after ejection will occur in or adjacent to the assembly with the ejected rod, and prior to ejection the power in this region will
necessarily be depressed. The hot spot analysis is performed using the detailed fuel and clad transient heat transfer computer code, FACTRAN (Ref. 2). This computer code calculates the transient temperature distribution in a cross section of a metal clad UO 2 fuel rod, and the heat flux at the surface of the rod, using as input the nuclear power versus time and the local coolant conditions. The zirconium-water reaction is explicitly represented, and all material properties are represented
as functions of temperature. A parabolic radial power distribution is used within the fuel rod. FACTRAN uses the Dittus-Boelter (Ref. 17) or Jens-Lottes (Ref. 18) correlation to determine the film heat transfer coefficient before DNB, and the Bishop-Sandburg-Tong correlation (Ref. 9) to determine the film boiling coefficient after DNB. The Bishop-Sandburg-Tong correlation is conservatively used, assuming zero bulk fluid quality. The DNBR is not calculated; instead the code is forced into DNB by specifying a conservative DNB heat flux. The gap heat transfer coefficient can be calculated by the code; however, it is adjusted in
order to force the full power steady state temperature distribution to agree
with the fuel heat transfer design codes. Further description of FACTRAN
appears in Section 15.0.11. 15.4-30 Rev. 13 WOLF CREEK System Overpressure Analysis Because safety limits for fuel damage specified earlier are not exceeded, there is little likelihood of fuel dispersal into the coolant. The pressure surge
may, therefore, be calculated on the basis of conventional heat transfer from
the fuel and prompt heat generation in the coolant. The pressure surge is calculated by first performing the fuel heat transfer calculation to determine the average and hot spot heat flux versus time. Using
this heat flux data, a THINC calculation is conducted to determine the volume surge. Finally, the volume surge is simulated in a plant transient computer code. This code calculates the pressure transient, taking into account fluid transport in the RCS and heat transfer to the steam generators. No credit is taken for the possible pressure reduction caused by the assumed failure of the
control rod pressure housing. The overpressure analysis is a generic analysis provided in Reference 6. The results of the generic analysis remain applicable to WCGS. 15.4.8.2.2 Calculation of Basic Parameters Input parameters for the analysis are conservatively selected on the basis of values calculated for this type of core. The more important parameters are discussed below. Table 15.4-2 presents the parameters used in this analysis. Ejected Rod Worths and Hot Channel Factors The values for ejected rod worths and hot channel factors are calculated, using either three-dimensional static methods or by a synthesis method employing one-
dimensional and two-dimensional calculations. Standard nuclear design codes
are used in the analysis. No credit is taken for the flux flattening effects
of reactivity feedback. The calculation is performed for the maximum allowed
bank insertion at a given power level, as determined by the rod insertion
limits. Adverse xenon distributions are considered in the calculation. Appropriate margins are added to the ejected rod worth and hot channel factors to account for any calculational uncertainties, including an allowance for
nuclear power peaking due to densification. Power distributions before and after ejection for a "worst case" can be found in Reference 6. During initial plant startup physics testing, ejected rod
worths and power distributions are measured in the zero and full power configurations and compared to values used in the analysis. It has been found that the ejected rod worth and power peaking factors are consistently
overpredicted in the analysis. 15.4-31 Rev. 11 WOLF CREEK Reactivity Feedback Weighting Factors The largest temperature increases, and hence the largest reactivity feedbacks, occur in channels where the power is higher than average. Since the weight of a region is dependent on flux, these regions have high weights. This means that the reactivity feedback is larger than that indicated by a simple channel analysis. Physics calculations have been carried out for temperature changes with a flat temperature distribution and with a large number of axial and radial temperature distributions. Reactivity changes were compared and
effective weighting factors determined. These weighting factors take the form of multipliers which, when applied to single-channel feedbacks, correct them to effective whole core feedbacks for the appropriate flux shape. In this analysis, since a one-dimensional (axial) spatial kinetics method is employed, axial weighting is not necessary if the initial condition is made to match the
ejected rod configuration. In addition, no weighting is applied to the moderator feedback. A conservative radial weighting factor is applied to the transient fuel temperature to obtain an effective fuel temperature as a function of time, accounting for the missing spatial dimension. These weighting
factors have also been shown to be conservative, compared to three-dimensional
analysis (Ref. 6). Moderator and Doppler Coefficient The critical boron concentrations at the beginning-of-life and end-of-life are adjusted in the nuclear code in order to obtain moderator density coefficient
curves which are conservative, compared to actual design conditions for the plant. As discussed above, no weighting factor is applied to these results. The Doppler reactivity defect is determined as a function of power level, using a one-dimensional steady state computer code with a Doppler weighting factor of 1.0. The Doppler defect used does not correlate to Figure 15.0-2 since the
TWINKLE computer code, on which the neutronic analysis is based, is a diffusion-theory code rather than a point-kinetics approximation. The Doppler
weighting factor will increase under accident conditions, as discussed above. Delayed Neutron Fraction, Calculations of the effective delayed neutron fraction ( eff) typically yield values no less than 0.70 percent at beginning-of-life and 0.50 percent at end-of-life for the first cycle. The accident is sensitive to if the ejected rod
worth is equal to or greater than as in zero power transients. In order to
allow for 15.4-32 Rev. 11 WOLF CREEK future cycles, conservative estimates of of 0.49 percent at beginning of cycle and 0.44 percent at end of cycle were used in the analysis. Trip Reactivity Insertion The trip reactivity insertion assumed is given in Table 15.4-2 and includes the effect of one stuck RCCA. These values are reduced by the ejected rod
reactivity. The shutdown reactivity was simulated by dropping a rod of the
required worth into the core. The start of rod motion occurred 0.5 seconds
after the high neutron flux trip point was reached. This delay is assumed to
consist of 0.2 second for the instrument channel to produce a signal, 0.15
second for the trip breaker to open, and 0.15 seconds for the coil to release
the rods. A curve of trip rod insertion versus time was used which assumed
that insertion to the dashpot does not occur until 3.3 seconds after the start of fall. The choice of such a conservative insertion rate means that there is
over 1 second after the trip point is reached before significant shutdown
reactivity is inserted into the core. This is particularly important
conservatism for hot full power accidents. The minimum design shutdown margin available for this plant at hot zero power (HZP) may be reached only at end-of-life in the equilibrium cycle. This value includes an allowance for the worst stuck rod and adverse xenon distribution, conservative Doppler and moderator defects, and an allowance for calculational
uncertainties. Physics calculations for this plant have shown that the effect
of two stuck RCCAs (one of which is the worst ejected rod) is to reduce the shutdown by about an additional 1 percent k. Therefore, following a reactor trip resulting from an RCCA ejection accident, the reactor will be subcritical when the core returns to HZP. Depressurization calculations have been performed for a typical four-loop plant, assuming the maximum possible size break (2.75-inch diameter) located in the reactor pressure vessel head. The results show a rapid pressure drop and a
decrease in system water mass due to the break. The safety injection system is actuated on low pressurizer pressure within 1 minute after the break. The RCS
pressure continues to drop and reaches saturation (1,200 psi) in about 2 to 3
minutes. Due to the large thermal inertia of primary and secondary systems, there has been no significant decrease in the RCS temperature below no-load by
this time, and the depressurization itself has caused an increase in shutdown margin by about 0.2 percent k due to the pressure coefficient. The cooldown transient could not absorb the available shutdown margin until more than 10 minutes after the break. The addition of 15.4-33 Rev. 11 WOLF CREEK borated safety injection flow starting 1 minute after the break is sufficient to ensure that the core remains subcritical during the cooldown. Reactor Protection As discussed in Section 15.4.8.1.1, reactor protection for a rod ejection is provided by high neutron flux trip (high and low setting) and high rate of
neutron flux increase trip. These protection functions are part of the reactor trip system. No single failure of the reactor trip system will negate the protection functions required for the rod ejection accident, or adversely affect the consequences of the accident. Major plant systems and equipment available for mitigation of transient and accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6. The actual parameters assumed and results are given in the respective section/subsection. Table 15.0-6 incorporates events shown in the sequence diagram, Figure 15.0-21. Results Cases are presented for both beginning and end-of-life at zero and full power.
- a. Beginning of cycle, full power
Control bank D was assumed to be inserted to its insertion limit. The worst ejected rod worth and hot channel factor were conservatively calculated to be 0.23 percent k and 5.7, respectively. The peak hotspot clad average temperature reached 2,401°F. The peak hot spot fuel center temperature reached melting at 4,900
°F. However, melting was restricted to less than 10 percent of the pellet.
- b. Beginning of cycle, zero power For this condition, control bank D was assumed to be fully inserted, and banks B and C were at their insertion limits. The worst ejected rod is located in control bank D and has a worth of 0.77 percent k and a hot channel factor of 10.7. The peak hotspot clad average temperature reached 2,954 °F. The peak hot spot fuel center temperature was 4,611 °F.
- c. End of cycle, full power Control bank D was assumed to be inserted to its insertion limit. The ejected rod worth and hot channel
factors were conservatively calculated to be 0.250 percent k and 6.3, respectively. The peak hotspot clad average temperature reached 2,325 °F. The peak hotspot fuel center temperature reached melting at 4,800°F. However, melting was restricted to less than 10 percent of the pellet. 15.4-34 Rev. 13 WOLF CREEK
- d. End of cycle, zero power The ejected rod worth and hot channel factor for this case were obtained, assuming control bank D to be fully inserted with banks B and C at their insertion limits.
The results were 0.86 percent k and 13.0, respectively The peak hotspot clad average temperature reached 2,967 °F.The peak fuel center temperature was 4,220 °F. A summary of the cases presented above is given in Table 15.4-2. The nuclear power and hot spot fuel and clad temperature transients for the worst cases (beginning-of-life, full power and beginning-of-life, zero power) are presented in Figures 15.4-22 through 15.4-25. The calculated sequence of events for the worst case rod ejection accidents, as shown in Figures 15.4-22 through 15.4-25, is presented in Table 15.4-1. For
all cases, reactor trip occurs very early in the transient, after which the
nuclear power excursion is terminated. As discussed previously in Section
15.4.8.2.2, the reactor will remain subcritical following reactor trip. The ejection of an RCCA constitutes a break in the RCS, located in the reactor pressure vessel head. The effects and consequences of loss-of-coolant accidents are discussed in Section 15.6.5. Following the RCCA ejection, the operator would follow the same emergency instructions as for any other loss-of-coolant accident to recover from the event. Fission Product Release It is assumed that fission products are released from the gaps of all rods experiencing DNB. In all cases considered, less than 10 percent of the rods
experienced the DNB. Although limited fuel melting at the hot spot was
predicted for the full power cases, in practice melting is not expected since
the analysis conservatively assumed that the hot spots before and after
ejection were coincident. Parameters assumed in the radiological consequences
analysis are summarized in Table 15.4-3. Pressure Surge A detailed calculation of the pressure surge for an ejection worth of one dollar at beginning-of-life, hot full power, indicates that the peak pressure
does not exceed that which would cause stress to exceed the faulted condition stress limits (Ref. 6). Since the 15.4-35 Rev. 13 WOLF CREEK severity of the present analysis does not exceed the "worst case" analysis, the accident for this plant will not result in an excessive pressure rise or
further damage to the RCS. Lattice Deformations A large temperature gradient will exist in the region of the hot spot. Since the fuel rods are free to move in the vertical direction, differential
expansion between separate rods cannot produce distortion. However, the
temperature gradients across individual rods may produce a differential
expansion tending to bow the midpoint of the rods toward the hotter side of the rod. Calculations have indicated that this bowing would result in a negative
reactivity effect at the hot spot since Westinghouse cores are under-moderated, and bowing will tend to increase the under-moderation at the hot spot. In
practice, no significant bowing is anticipated, since the structural rigidity
of the core is more than sufficient to withstand the forces produced. Boiling
in the hot spot region would produce a net flow of coolant away from that
region. However, the heat from the fuel is released to the water relatively
slowly, and it is considered inconceivable that cross flow will be sufficient
to produce significant lattice forces. Even if massive and rapid boiling, sufficient to distort the lattice, is hypothetically postulated, the large void fraction in the hot spot region would produce a reduction in the total core moderator to fuel ratio, and a large reduction in this ratio at the hot spot.
The net effect would therefore be a negative feedback. It can be concluded
that no conceivable mechanism exists for a net positive feedback resulting from
lattice deformation. In fact, a small negative feedback may result. The effect
is conservatively ignored in the analysis. 15.4.8.3 Radiological Consequences 15.4.8.3.1 Method of Analysis 15.4.8.3.1.1 Physical Model Prior to the accident, it is assumed that the plant has been operating with simultaneous fuel defects and steam generator tube leakage for a time sufficient to establish equilibrium levels of activity in the reactor coolant
and secondary systems. The RCCA ejection results in reactivity being inserted to the core which causes the local power to rise. In a conservative analysis, it is assumed that partial cladding failure and fuel melting occurs. The fuel pellet and gap activities are assumed to be immediately and uniformly released within the
reactor coolant. 15.4-36 Rev. 11 WOLF CREEK Two release paths to the environment exist which are analyzed separately and conservatively, as if all the activity is available for release from each path. The activity released to the containment from the reactor coolant through the ruptured control rod mechanism pressure housing is assumed to be mixed
instantaneously throughout the containment and is available for leakage to the atmosphere. The only removal processes considered in the containment are iodine plateout, radioactive decay, and leakage from the containment. The model for the activity available for release to the atmosphere from the relief valves assumes that the release consists of the activity in the
secondary system plus that fraction of the activity leaking from the reactor
coolant through the steam generator tubes. The leakage of reactor coolant to
the secondary side of the steam generator continues until the pressures in the
reactor coolant and secondary systems equalize. Primary and secondary pressures are equalized at 1100 seconds following the accident, thus terminating primary to secondary leakage in the steam generators. Refer to Figures 15.4-26 and 15.4-27. Thereafter, no mass transfer from the reactor coolant system to the secondary system due to the steam generator tube leakage is assumed. Thus, in the case
of coincident loss of offsite power, activity is released to the atmosphere from a steam dump through the relief valves. 15.4.8.3.1.2 Assumptions and Conditions The major assumptions and parameters used in the analysis are itemized in Tables 15.4-3 and 15A-1 and summarized below. The assumptions are consistent
with Regulatory Guide 1.77. The assumption used to determine the initial concentrations of isotopes in the reactor coolant and secondary coolant prior to the accident are as follows:
- a. The reactor coolant iodine activity is based on the dose equivalent of 1.0 Ci/gm of I-131.
- b. The noble gas and iodine activity in the reactor coolant are based on 1-percent failed fuel.
- c. The secondary coolant activity is based on the dose equivalent of 0.1 Ci/gm of I-131. 15.4-37 Rev. 11 WOLF CREEK The following conditions are used to calculate the activity released and the offsite doses following a RCCA ejection accident. a. 10 percent of the fuel rod gap activity, except for Kr-85 and I-131, which are 30 percent and 12 percent respectively, is additionally released to the reactor coolant.
- b. 0.25 percent of the fuel is assumed to melt.
- c. Following the incident until primary and secondary side pressures equalize, secondary steam is released to the
environment. The total quantity of steam released is
given in Table 15.4.3.
- d. The 1-gpm primary-to-secondary leak to the unaffected steam generators.
- e. All noble gas activity in the reactor coolant which is transported to the secondary system via the primary-to-
secondary leakage is assumed to be immediately released
to the environment.
- f. Fission products released from the fuel-cladding gap of the damaged fuel rods are assumed to be instantaneously and homogeneously mixed with the reactor coolant.
- g. The iodine activity present in the primary to secondary leakage is assumed to mix homogeneously with the iodine
activity initially present in the steam generators.
- h. A partition factor of 0.1 between the vapor and liquid phases for radioiodine in the steam generators is utilized to determine iodine releases to the environment via steam venting from the steam generators.
- i. The activity released from the steam generators is immediately vented to the environment.
- j. The containment is assumed to leak at 0.2 volume percent/day during the first 24 hours immediately following the accident and 0.1 volume percent/day thereafter.
- k. No credit is taken for radioactive decay or ground deposition during radioactivity transport to offsite
location. 15.4-38 Rev. 13 WOLF CREEK
- l. Short-term accident atmospheric dispersion factors corresponding to ground level releases, breathing rates, and dose conversion factors are given in Table 15A-2, and 15A-4, respectively.
- m. Offsite power is assumed lost.
15.4.8.3.1.3 Mathematical Models Used in the Analysis
Mathematical models used in the analysis are described in the following sections: a. The mathematical models used to analyze the activity released during the course of the accident are described in Appendix 15A.
- b. The atmospheric dispersion factors used in the analysis were calculated based on the onsite meteorological measurement programs described in Section 2.3 and are
provided in Table 15A-2.
- c. The thyroid inhalation and total-body immersion doses to a receptor at the exclusion area boundary or outer boundary of the low-population zone were analyzed, using the models described in Appendix 15A.
15.4.8.3.1.4 Identification of Leakage Pathways and Resultant Leakage Activity The leakage pathways are:
- a. Direct steam dump to the atmosphere through the secondary system relief valves for the secondary steam
- b. Primary-to-secondary steam generator tube leakage and subsequent steam dump to the atmosphere through the
secondary system relief valves
- c. The resultant activity released to the containment is assumed available for leakage directly to the environment.
Table 15.4-3 shows the total curies released
15.4.8.3.2 Identification of Uncertainties and Conservative Elements in the Analysis
- a. Reactor coolant and secondary coolant activities of 1 percent failed fuel and 0.1 Ci/gm I-131 dose equivalent, respectively, are many times greater than assumed for normal operation conditions. 15.4-39 Rev. 11 WOLF CREEK
- b. A 1-gpm steam generator primary-to-secondary leakage, which is significantly greater than that anticipated
during normal operation, is assumed.
- c. The coincident loss of offsite power with the occurrence of a RCCA ejection accident is a highly conservative assumption. In the event of the availability of offsite station power, the condenser steam dump valves will
open, permitting steam dump to the condenser. Thus there is no direct release via that path to the
environment.
- d. It is assumed that 50 percent of the iodines released to the containment atmosphere is adsorbed (i.e. plate out) onto the internal surfaces of the containment or adheres to internal components. However, it is estimated that the removal of airborne iodines by various physical
phenomena such as adsorption, adherence, and settling could reduce the resultant doses by a factor of 3 to 10.
- e. The activity released to the containment atmosphere is assumed to leak to the environment at the containment
leakage rate of 0.2-volume percent/day for the first 24
hours and 0.1-volume percent/day thereafter. The initial
containment leakage rate is based on the peak calculated
internal containment pressure anticipated after a LOCA.
The pressures associated with a RCCA ejection accident
are considerably lower than that calculated for a LOCA.
The pressure inside the containment also decreases
considerably with time, with an expected decrease in
leakage rates. Taking into account that the containment
leak rate is a function of pressure, the resultant doses
could be reduced by a factor of 5 to 10 (Ref. 10).
- f. The meteorological conditions which may be present at the site during the course of the accident are uncertain.
However, it is highly unlikely that the meteorological
conditions assumed will be present during the course of
the accident for any extended period of time. Therefore, the radiological consequences evaluated, based on the
meteorological conditions assumed, are conservative. 15.4.8.3.3 Conclusions 15.4.8.3.3.1 Filter Loadings The only ESF filtration system considered in the analysis which limits the consequences of the RCCA ejection accident is the control room filtration system. Activity loadings on the control 15.4-40 Rev. 11 WOLF CREEK room charcoal filter are based on the flow rate through the filter, the concentration of activity at the filter inlet, and the filter efficiency. The activity in the control room filter as a function of time has been evaluated for the loss-of-coolant accident, Section 15.6.5. Since the control
room filters are capable of accommodating the potential design-basis loss-of-coolant accident fission product iodine loadings, more than adequate design margin is available with respect to postulated RCCA ejection accident releases. 15.4.8.3.3.2 Doses to Receptor at the Exclusion Area Boundary and Low-Population Zone Outer Boundary The potential radiological consequences resulting from the occurrence of a postulated RCCA ejection accident have been conservatively analyzed, using assumptions and models described in previous sections. The total-body doses due to immersion from direct radiation and the thyroid dose due to inhalation have been analyzed for the 0-2 hour dose at the exclusion area boundary and for the duration of the accident at the low-
population zone outer boundary. The results are listed in Table 15.4-4. The resultant doses are well within the guideline values of 10 CFR 100. 15.4.8.4 Conclusions Even on a conservative basis, the analyses indicate that the described fuel and clad limits are not exceeded. It is concluded that there is no danger of
sudden fuel dispersal into the coolant. Since the peak pressure does not exceed that which would cause stresses to exceed the faulted condition stress
limits, it is concluded that there is no danger of further consequential damage
to the RCS. The analyses have demonstrated that upper limit in fission product
release as a result of a number of fuel rods entering DNB amounts to 10
percent.The RCS integrated break flow to containment following a rod ejection accident is shown in Figure 15.4-28. 15.
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1961.
- 19. Paulsen, M. P., et al. "RETRAN-3D - A Program for Transient Thermal Hydraulic Analysis of Complex Fluid Flow Systems," EPRI-NP-7450(A), July 2001.
15.4-42 Rev. 25 WOLF CREEK TABLE 15.4-1 TIME SEQUENCE OF EVENTS FOR INCIDENTS WHICH RESULT IN REACTIVITY AND POWER DISTRIBUTION ANOMALIES
Accident Event Time (sec) Uncontrolled RCCA bank Initiation of uncontrolled 0.0 withdrawal from a rod withdrawal from 10 -9 of subcritical or low nominal power power startup condition Power range high neutron 10.36 flux low setpoint reached
Peak nuclear power occurs 10.50
Rods begin to fall into 10.86 core
Minimum DNBR occurs 12.6 Peak average clad tempera- 12.50 ture occurs
Peak average fuel temperaure occurs 12.80
Peak heat flux occurs 12.90
Uncontrolled RCCA Initiation of uncontrolled 0.0 bank withdrawal at RCCA withdrawal at 39 pcm/sec,
Power (DNB) 100% power, EOL Overtemperature T 27.75 reactor trip signal initiated
Maximum DNB occurs 28
Uncontrolled RCCA Initiation of uncontrolled 0.0 Bank withdrawal at RCCA withdrawal at 45 pcm/sec, Power (RCS pressure) 10% power, BOL
High pressurizer pressure 16.05 reactor trip signal initiated Maximum pressurizer 16.6 pressure
Rev. 25 WOLF CREEK TABLE 15.4-1 (Sheet 2) Time Accident Event (sec) Uncontrolled RCCA bank withdrawal at power (pressurizer fill) Initiation of uncontrolled RCCA withdrawal at 8 pcm/sec, 10% power, EOL Maximum pressurizer level Overtemperature reactor trip signal initiated 0.0 670 672 Startup of inactive reactor coolant loop at an incorrect temperature Initiation of pump startup
Power reaches P-8 trip setpoint 1.0
12.8 Rods begin to drop 12.9 Minimum DNBR occurs 12.9
Rod cluster control assembly ejection accident
- 1. Beginning-of-life, full Initiation of rod ejection 0.0 power Power range high neutron flux setpoint 0.05 reached
Peak nuclear power occurs 0.135
Rods begin to fall into core 0.55
Peak clad temperature occurs 2.41
Peak heat flux occurs 2.42
Peak fuel centerline temperature 3.07
- 2. End-of-life, zero power Initiation of rod ejection 0.0
Power range high neutron flux low 0.14 setpoint reached Peak nuclear power occurs 0.17
Rods begin to fall into core 0.64
Peak heat flux occurs 0.96
Peak clad temperature occurs 1.00
Peak centerline fuel temperature 2.96
Rev. 25 WOLF CREEK TABLE 15.4-2 PARAMETERS USED IN THE ANALYSIS OF THE ROD CLUSTER CONTROL ASSEMBLY EJECTION ACCIDENT Time in Life HZP (Beginning) HFP (Beginning) HZP (End) HFP (End)Power level, %01020102 Initial average coolant temperature, F557.0594.9557.0594.9Ejected rod worth, %Dk0.770.230.860.25Delayed neutron fraction, %0.49 0.490.440.44 Feedback reactivity
weighting2.3981.303.55 1.30Trip reactivity, %Dk1.34.01.3 4.0 F Q before rod ejection2.322.32 F Q after rod ejection10.7 5.7 13.0 6.3Number of operational pumps2424 Fuel Melt 0.0 9.3 0.0 9.0 Maximum fuel center temperature, F 461149004220 4800 Maximum clad average temperature, F 2954 2401 2967 2325 Maximum fuel stored energy, Btu/lbm 311332295 319 Rev. 10 WOLF CREEK TABLE 15.4-3 PARAMETERS USED IN EVALUATING THE RCCA EJECTION ACCIDENTI.Source Dataa.Core power level, MWT3565b.Burnup, full power days1000c.Core inventoriesTable 15A-3d.Steam generator tube leakage, gpm1e.Reactor coolantBased on 1-percent failed fuel, provided in Table 11.1-5f.Secondary system activityBased on 1-percent failed fuel, 4 times the values provided in Table 11.1-4g.Extent of core damage10 percent of fuel rods experience cladding failure; 0.25 percent of fuel experiences meltingh.Activity released to reactor coolant, percent1.Cladding failure(a)Noble gas gap activity100(b)Iodine gap activity1002.Fuel melting(a)Noble gas gap activity100(b)Iodine fuel activity50i.Iodine carryover factor for steam0.1 generatorsj.Reactor coolant mass, lbs4.94E + 5k.Steam generator mass, lbs/steam1.04E + 5 generator Rev. 7 WOLF CREEK TABLE 15.4-3 (Sheet 2)II.Atmospheric Dispersion FactorsTable 15A-2III.Activity Release Dataa.Containment volume, ft 3 2.5E + 6b.Containment leak rate, volume percent/day1.0-24 hours0.20 2.1-30 days0.10c.Percent of containment leakagethat is unfiltered100d.Plateout of iodine withincontainment, percent50e.Offsite powerLostf.Steam release from relief valves,48,600 lbsg.Duration of release from relief140 valves, sech.Activity released to the environment via steam release and containment releaseSteam GeneratorContainment Release (Ci)Release (Ci)Isotope0-2hr 0-2hr 0-30 daysI-1315.369E+001.040E+027.275E+03I-1326.546E+009.655E+012.139E+02I-1339.393E+001.769E+022.142E+03I-1349.937E+001.012E+021.275E+02I-1358.703E+001.554E+028.184E+02Xe-131m5.287E-012.225E+002.028E+02Xe-133m3.038E+001.265E+013.124E+02Xe-1339.881E+014.146E+022.087E+04Xe-135m1.768E+011.469E+011.476E+01Xe-1352.325E+019.114E+015.940E+02Xe-1376.881E+011.640E+011.640E+01Xe-1387.650E+015.812E+015.829E+01Kr-83m6.080E+001.810E+013.400E+01Kr-85m1.316E+014.788E+011.774E+02Kr-851.392E+005.874E+001.079E+03Kr-872.521E+016.547E+019.863E+01Kr-883.580E+011.201E+023.105E+02Kr-893.454E+017.095E+007.095E+00 Rev. 13 WOLFCREEKTABLE15.4-4RADIOLOGICALCONSEQUENCESOFAROD-EJECTIONACCIDENTWolfCreekDose(rem)ExclusionAreaBoundary(0-2hr)Thyroid1.17E+1Wholebody5.85E-2LowPopulationZoneOuterBoundary (duration)Thyroid1.44E+1Wholebody2.34E-2Rev.13 v 1.2 1 -0.8 c !o.a NudlwPwlr ... I a. 0.4 0.2 1-0 0 5 10 15 Tima(sec) 20 25 30 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGORB 15.4-1 Core*Average Neutron Plux Transient for Uncontrolled Rod Withdrawal from a Subcritical Condition Rev.10 0.5...----------------------, 0.4 fu -J 0.2 0.1 0 5 10 16 20 25 30 *;!"* Tlme(IIC) WOLF CRBBK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-2 Thermal Flux Transient for Uncontrolled Rod Withdrawal from a Subcritical Condition Rev.10 i I. 720 700 880 1840 1820 Jeoo ... 580 580 540 585 580 $715 I tm . -F 580 555 fUIIAVIIIII 0 6 a. .... 0 10 10 15 Tlme(eiC) 15 Time (ac) 20 20 *--*-*--------- 2& so 25 30 WOLF CREEK UPDATED SAFETY ANALYSIS RBPORT FIGURE 15.4-3 Fuel and Clad Temperature Transient for uncontrolled Rod Withdrawal from a Subcritical Condition Rev.10 1.4 ,..----------------, ... 5 1.2 0.. 1 ! B o.s i 0.6 .!::1 1 o.4 0.2 --------*-----*----------
**--
*******----
*---
*-****-*--------
0 20 40 60 80 100 Time (secqnds) WOLF CRBEK UPDATBD SAFBTY ANALYSIS REPORT FIGORB 15.4*4 Uncontrolled RCCA Bank Withdrawal from Pull Power with Minimum Reactivity Feedback (5 pcm/sec Withdrawal Rate) Rev.10 Uncontrolled RCCA Bank Withdrawal from Full PowerDNB Limiting Case 0 20 40 60 80 100 12001020304050607080Elapsed Time (sec) Core Power (% RTP)100% RTP, EOL, 39 pcm/sec, Peak Value = 118.1 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-4a, Core Power Uncontrolled RCCA Bank Withdrawal at Power (DNBLimitingCase) Uncontrolled RCCA Bank Withdrawal from Full PowerDNB Limiting Case 20002050210021502200225023002350240001020304050607080Elapsed Time (sec)Pressure Core Exit (psia)100% RTP, EOL, 39 pcm/sec, Peak Value = 2351.81 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-4b, Core Exit Pressure Uncontrolled RCCA Bank Withdrawal at Power (DNBLimitingCase) Uncontrolled RCCA Bank Withdrawal from Full PowerDNB Limiting Case 565570575580 585 590 595 60001020304050607080Elapsed Time (sec)Tavg (degF)100% RTP, EOL, 39 pcm/sec, Peak Value = 599.5 7 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-4c, RCS Tavg Uncontrolled RCCA Bank Withdrawal at Power (DNBLimitingCase) Uncontrolled RCCA Bank Withdrawal from Full PowerDNB Limiting Case 0 0.2 0.4 0.6 0.8 1 1.2 1.401020304050607080Elapsed Time (sec) Heat Flux to Flow (ratio)100% RTP, EOL, 39 pcm/sec, Peak Value = 1.2 3 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-4d, Flux Ratio Uncontrolled RCCA Bank Withdrawal at Power (DNBLimitingCase) Uncontrolled RCCA Bank Withdrawal from Full PowerDNB Limiting Case 555 560 565 570 575 580 585 59001020304050607080Elapsed Time (sec) Enthalpy Core Top Volume (BTU/lbm)100% RTP, EOL, 39 pcm/sec, Peak Value = 586.16 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-4e, Core Exit Enthalpy Uncontrolled RCCA Bank Withdrawal at Power (DNBLimitingCase) Uncontrolled RCCA Bank Withdrawal from Full PowerDNB Limiting Case 2.422.432.442.452.462.472.482.49 2.52.512.5201020304050607080Elapsed Time (sec)Core Inlet Flow (Mlbm/hrft2)100% RTP, EOL, 39 pcm/sec, Peak Value = 2.51 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-4f, Core Inlet Flow Uncontrolled RCCA Bank Withdrawal at Power (DNBLimitingCase) 1.52.02.53.0 3.54.04.5 5.0 0 5 10 15 20 25 30Time (sec.) Minimum DNBR WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-4g, Minimum DNBR Uncontrolled RCCA Bank Withdrawal at Power (DNBLimitingCa se)
-.!1
- a. -2400 ! = l.2200 ft "§2000
- I ------------*--------------------------
Q. 1800 0 20 40 80 80 100 Time (seconds)
- -*-------------------------------------
*-**----------
..... 0 20 40 60 80 100 nme (seconds) Rev. 10 WOLP CREBIC UPDATED SAFETY ANALYSIS REPORT PIGORB 15.4-5 Uncontrolled RCCA Bank Withdrawal from Full Power with Minimum Reactivity Feedback (5 pcm/sec Withdrawal Rate) 1.8 1.9 2 2.1 2.2 2.3 2.4 2.50102030405060708090100Insertion Rate (pcm/sec) Minimum DNBRMinimum FeedbackMaximum Feedback WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-5a, Minimum DNBR Uncontrolled RCCA Bank Withdrawal at Power (100%Power) 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.401020304 0506 0708 0901 0 0Insertion Rate (pcm/sec) Minimum DNBRMinimum FeedbackMaximum Feedback WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-5b, Minimum DNBR Uncontrolled RCCA Bank Withdrawal at Power (60%Power) 1.92.1 2.32.52.7 2.9 3.13.33.50102030405060708090100Insertion Rate (pcm/sec) Minimum DNBRMinimum FeedbackMaximum Feedback WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-5c, Minimum DNBR Uncontrolled RCCA Bank Withdrawal at Power (10%Power) I = a I _820 u. ":' 610 Eeoo c:sso Cl gsao <J G) 570 Q l!seo I C( 550 0 20 40 60 80 100 Time (seconds) 5.0 ,..-------------------------------.. 4.5 4.0 3.S 1---------------------------------------* -------------------------*--1------------------------------------------------------------------ 2.J 10
u 0 10 lO Tlllle(IIL) 30 -lgure Wrtbdrawal From Full Power with BegiJmi12g-of-Life Reactivity (S pcmlsec W"rthd.rawal Rate) Rev.10 Uncontrolled RCCA Bank Withdrawal from Full PowerOver Pressure Limiting Case 0 20 40 60 80100 120051015202530Elapsed Time (sec) Core Power (% RTP)10% RTP, EOL, 41 pcm/sec, Peak Value = 114.56 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-6a, Core Power Uncontrolled RCCA Bank Withdrawal at Power (RCSOverpressureLimitingCase) Uncontrolled RCCA Bank Withdrawal from Full PowerOver Pressure Limiting Case 560565570575580585590595051015202530Elapsed Time (sec) Tavg (degF)10% RTP, EOL, 41 pcm/sec, Peak Value = 590.41 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-6b, RCS Tavg Uncontrolled RCCA Bank Withdrawal at Power (RCSOverpressureLimitingCase) Uncontrolled RCCA Bank Withdrawal from Full PowerOver Pressure Limiting Case 2200 2300 2400 2500 2600 2700 0 5 1015 20 25 30Elapsed Time (sec)Pressure RCS Lower Head (psia)10% RTP, EOL, 41 pcm/sec, Peak Value = 2733.97 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-6c, Maximum RCS Pressure Uncontrolled RCCA Bank Withdrawal at Power (RCSOverpressureLimitingCase)
2.15 2.10 ** ** .. **. .. ** . .. .. ** *. _.AI'/ OT4TTrip 1.90 t.U .. .... ** .** . . *.** . . *** .. .. *** .. **"' .. .. .** ** *... ** uG, L ------:z.L.....-....:.l _ _._--!..,- ........ ........ 0 Updated Safety ADalysis Report *guze IS. 1 M"mimum DNBR Vs. Raclivity lnseniOD Rare, Rod W"rtbdrawal fiom JOO%Power Rev.10 Uncontrolled RCCA Bank Withdrawal from Full PowerOver Fill Limiting Case 0 10 20 30 40 50 60 70 80 901000100200300400500600700800Elapsed Time (sec) Core Power (% RTP)10% RTP, EOL, 8 pcm/sec, Peak Value = 93.95 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-7a, Core Power Uncontrolled RCCA Bank Withdrawal at Power (PressurizerOverfillLimitingCase) Uncontrolled RCCA Bank Withdrawal from Full PowerOver Fill Limiting Case 5605705805906006106200100200300400500600700800Elapsed Time (sec) Tavg (degF)10% RTP, EOL, 8 pcm/sec, Peak Value = 616.29 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-7b, RCS Tavg Uncontrolled RCCA Bank Withdrawal at Power (PressurizerOverfillLimitingCase) Uncontrolled RCCA Bank Withdrawal from Full PowerOver Fill Limiting Case 30 40 50 60 70 80 90 1000100200300400500600700800Elapsed Time (sec)Level PZR (% of Total)10% RTP, EOL, 8 pcm/sec, Peak Value = 97.6 4 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-7c, Pressurizer Level Uncontrolled RCCA Bank Withdrawal at Power (PressurizerOverfillLimitingCase)
"This Figure has been deleted."
Rev. 25 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-8 Minimum DNBR Vs. Reactivity Insertion Rate, Rod Withdrawal from 60% Power
"This Figure has been deleted."
Rev. 25 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-9 Minimum DNBR Vs. Reactivity Insertion Rate, Rod Withdrawal from 10% Power
-* c z i 1.1 0 1.0 z 0 ;::: u 0.1 il ... -o.a I i 0.7 z 0.1 0.1 0 10 100 110 200 nMI ISICONDIJ 18v.7 WOLF CREEK UPDATED SAFETY ANALYSIS REPOR'l' FIGURE 15.4-10 NUCLEAR POWER TRANSIEN'l' AND CORE HEA'l' FLUX 'l'RANSIENT FOR DROPPED* ROD CLOSTER CONTROL ASSEMBLY -u.. 0 -w a: :;::) a: w CL :E w ... w CJ c a: w _, *w en en w >* -c( en -w a: :;::) en en W* a: > a: c( -a: *--***-------- WOLP CREEK 600 580 ....._-660 f-540 520 I I I 2400 2300 2200 2100 2000 1900 0 50 100 150 200 TIME (SECONDS) WOLF CREEK UPDATED SAFETY JOO\l,YSIS REPORT FIGURE 15.4-lla PRESSURIZER PRESSURE TRANSIENT AND CORE AVERAGE TEMPERATURE TRANSIENT FOR DROPPED ROD CLUSTER CONTROL ASSEMBLY
lu* 1!5 . lu" IDA* !D.2-\ liE(SECorm) Rev. 7 WOLF CREEK UPJl&ftl) SAI'nY ANALYSIS JU:PORT FIGORI 15.4-12 NUCLEAR POWER TRANSIENT FOR S'rAilTUP OF AN INAC!IVE REAC'l'OR COOLMT LOOP
- CREER ;:,; UPl'ATl:;J}
SArE't'Y REPORT *CORt ri.Ol'tl ttl.J\NS I ENT FOF. S"rARTU!F OF AN REACTOR COOLJ\NT I.OOP I ' I ' I
1.1000 10 40 Rev. 7 WOLF CREEK UPDJ\TED SAI'E'l'Y ANALYSIS REPORT FIGURE 15.4-14 PRESSURIZER PRESSURB TMHSIEHT FOR STARTUP OF AN INACTIVE REACTOR COOIJUn' LOOP . . liE (aU>>>JS) Rev. U FIGURE 15.4-15 CORE AVDAGE TEKPBRATURE TIWlSIEN'l' FOR STM'l'UP OF AN INACTIVE REACTOR COOLANT LOOP II S.l . 2 !PNIR lnl* , .. t.5 I 0 5 ...; --I l 10 ,, 20 nne (secondl) Rev. 7 WOLF CREEK UPDM'ED SAFETY .ANALYSIS IU:POR'l" nGORE 15.4-16 DNBR 'rlWISlEH'l' FOP. S'l'Al\TUP OF AN INACTIVE REACTOR COOLANT LOOP R PI M L 1.1 H G FED C 8 A ..... 1-7.9 a.a **** -***
- 7.7 'r-1.7 -7.3 *5.1 1-1.1 *3.11 1--5.3 -1.8 *** o.7 2.5 t.l **** -7.11 e.a -*** -a.s -1.2 f-t. I -*** 0.2 _,_, .. ... *3.1 1-1.1 ..... f-0.3 1-$.0 *** 2 t-1.0
- 5 3..2 3.11 3.& 2.7 5.1 6.0 0.7 10.6 s.e 17. I ..... 11.3 211.1 7.7 23.6 .. ., 11.1 17.6 &.5 CASE A lloY.7 WOLF CUltlt UPDABD SAF£1.'Y JUIALYSIS REPOa'l 2 3 IJ 5 6 7 8 I J 12 13 II& 15 riGOR& 15.4-17 1\EPl\ESEtftA'IIVE PDCD"l' CH1\NGB IN ,
- LOCAL ASSDIBLY AV&RAG8 POWER FOR \.,J Alf IBTDCIIAlfGE BETIIIIH A 1\EGIOlf 1 AND A REGICII 3 ASSEMBLY R P N M L K J H G FE DC B A -GA -4.1 * *2.8 *3.1 -3.8 -3.1 -3.8 -3.8 -3.8 -3.1 -3.4 *2.8 -3.2 *1.7 .z.z *1.0 o.o 1.2 o.o 3.2 0.3 -4.1 -2.0 -G.7 0.& 0.8 -4.1 1 -4.8 2 ..... -4.4 *2.8 1.4 3 4 -4.3 -4.8 *1.1 -5 *2.1 0.1 -8 *2.31 2.2 -' ' 11A 11.3 &.8 4.4 -8 &.2 18.7 5.4 -9 8.1 10 -2.2 8.1 8.8 -1 1 2.8 8.1 -. 2 1.1 10.3 1 3 3.2 6.0 1 4 1.& . & CASEB-1 :a.v.7 WOLF CREEK UPDM'ED SAFETY ANALYSIS REPORT FIGURE 15.4-18 REPRESEN"lATIVE PEP.CEN'l' CBAHGZ IN LOCAL ASSEMBLY AVERAGE P01ID !'OP. AN :nrrEP.CJIANGB BETIIEElf A REGION 1 AND A REGION 2 ASSEMBLY WITH THE BtJ:RHABLE POISOH RODS DING RETAINED BY !HE REGION 2 ASSEMBLY R P. I M L I .J N I F E D C I A 1.1 1.0 1.7 1.7 1.1 ' 0.2 *** o.o -o.7 -o.e o.a *1.0 lf -o.t -** 7 1-LS 0.7 -*** 2.3 -2.1 1.0 ** I 1.0 1.1 I. I '*' *** * ** 5.2 LZ 1.1 1.& 1-t. I *I. I -2.1 -2 ** -2.1 *2*' -z.a *** ll.t 1.1 0.7 ..o -0.3 -o.a -o.l -o.7 o.a -1.3 1-l.7 f-1,1 2.5 -o.a CASE 1*2 WOLF caEElC .... -o.t 2 3 " 5 6 7 a 9 10 II 12 I I I 3 ' 5 Rev.1 UPDATED SAFETY ANALYSIS REPC>aT FIGORZ 15.4-19 U:PRESEN'l'ATIVE PDCIN'r CHANGE IN LOCAL ASSEMBLY AV'DAGB P01ID FOR AH IN'l'DCIIANG&
BE'1'11ED A REGIO!f 1 AND A REGION 2 .ASSEMBLY WITH 'fH& BlJINABLE POISON RODS BEING omANS!EUED TO 'fBE REGION 1 l } ASSEMBLY '-' I P I M L I II I F E D C I A a.o -a.o ... , -o ** *Lt ..* Ll *LI .. , ' *LI **** * ** ILl *1.2 o.a '*' **** .... '*' ..... Ll *LI **** *Ll 4.1 **** * *** ..... 1.1 .. , ..... D<J .... .. ., ***
- LI *1.2 * *** 2.0
- Z.O *I,J' .. **** *LI '*' -o.t -o.s **** z.o ... CASE C WOLF CUEK *L2. **** . 2 3 " s e 7
- 9 10 II 12 13 ., IS bv. 1 UPDA'l'ED SAFETY ANALYSIS REPORT FIGURE 15.4-20 REPRESENTA!IVE PERCEHT CHANGE IJf LOCAL ASSEMBLY AVIMGE POWER 1'01. AN ENRICHMENT EIJ.OR (A REGIOH 2 ASSDIBLY LOADED IHTO '1'BE COR! CElft'ML POSITION)
. . a P IM \.I J I IF l D tl * *** **** .. , 1.1 **** *** 7.1 .... t.J *** 17.1 .... 2P.J 11.7 Ita. a [X U.l ... , *** .... *** II.J *II _,, *II 2 *II .. , .. , *13 3 *II " *II *II * ** 5 .... * ** 5
- II ... 7 0.1 *** *" *II *** I *II *II ! ... *II 10 *** ... .. *IJ " . t-1.7 .... 12 Z.l 1-7.0 13 7.0 *LJ ... , 116 Z.l 15 CASED Rev.7 . WOLF CREEK OPDA!ED SAFETY REPORT FIGOU 15.4-21 REPP.ESDrrA'riVB PDCEN'f CHUGB IN LOCAL ASSDIBLY AVEUG!! P01ID. FOR LOADING A REGION 2 ASSEMBLY INTO A 0 1\EGIOH 1 POSI'flOH NEAR THE CORE L } PERIPHERY
'-'
-1.5 & I 1 1 !:. .. I o.s 0 1 2 3 4 6 6 7 Tlnii(IIO) WOLF CREBX OPDATBD SAnTY ANALYSIS RBPORT FIGCRB 15.4-22 Nuclear Power Transient, BOL, BPP, Rod Bjection Accident Rev.10 6,000 .-------------------------, , 1,000 ,' -, 0 1 2 3 4 5 8 7 Tlme(uc) WOLF CRBBK UPDATED SAFETY ANALYSIS REPORT FIGURB 15.4-23 FUel Centerline, Fuel Average, and Cladding SUrface Temperature Transients, BOL, HPP, Rod Ejection Accident Rev.10 I.
0 1 2 3 4 5 8 7 Tlme(uc) WOLF CREEK UPDATED SAFE'1'Y ANAI.YSIS REPORT FIGURE 15.4-24 Nuclear Power Transient, EOL, HZP, Rod Ejection Accident Rev. 10 5,000 ,-----------------------, 4,000
.... *************
- .. -.. --........ -............ . .-------.....__.
--....... ............... -....._ *-***---..-...-. r "a 31000 .,.------.... _ -! , .... ' ..... "' I .,,..,_ : ' -----' ' I --....... __ _ 1,000 : I 0 1 2 3 .. 5 -:r-8 7 Time(MO) WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURB 15.4-25 Fuel Centerline, Fuel Average, and Cladding SUrface Temperature Transients, EOL, HZP, Rod Ejection Accident Rev. 10 2000 > a: c( Q 1500 z o-w-rnle -a:w Oa: 1000 !(:;, a::g """" Za: ""* (,:, 500 c( w 0 0 250 500 WOLF CREEK 750 1000 1250 1600 17&0 T'ME (SECONDS) Rev.12 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT Figure 15.4-28 STEAM GENERATOR SECONDARY PRESSURE TRANSIENT FOR ROD EJECTiON ANALYSIS WOLF CREEK 2000 *-*-*---*-*-------*-**-*-
- -**---*-**
-<l u; !: 1500 w a: ;:) en en w a: 1000 a. en (J a: 500 . -----* . . .. ' .. -----. _________ , ___ -* ... -....... -*--*** *--*-** .... --** *-*** R.ev.7 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.4-27 RCS PRESSURE TRANSIENT FOR ROD EJECTION ANALYSIS v: 10.0 -9.0 "'
- 0 8.0 X CD 7.0 _, =-6.0 0 _, "-loo= 5.0 < "" a:: 3.0 w 1-a= 2.0 c:::ll .... z 1.0 G 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 11.0 TIM£ (SECONDS x lo-3) Rav.7 WOLF CREEK UPDATED SAFETY ANALYSIS UPORT FIGURE 15.4-28 REACTOR COOLANT SYSTEM IN'l'EGRATED BREAK FLOW FOLLOWING A ROD EJECTION ACCIDENT WOLF CREEK 15.5 INCREASE IN REACTOR COOLANT INVENTORY Discussion and analysis of the following events are presented in this section:
- a. Inadvertent operation of the emergency core cooling system during power operation.
- b. Chemical and volume control system malfunction that increases reactor coolant inventory.
- c. A number of BWR transients. (Not applicable to WCGS).
These events, considered to be ANS Condition II, cause an increase in reactor coolant inventory. Section 15.0.1 contains a discussion of ANS classifications. 15.5.1 INADVERTENT OPERATION OF THE EMERGENCY CORE COOLING SYSTEM DURING POWER OPERATION 15.5.1.1 Identification of Causes and Accident Description Spurious emergency core cooling system (ECCS) operation at power could be caused by operator error or a false electrical actuation signal. A spurious
signal may originate from any of the safety injection actuation channels, as
described in Section 7.3. Following the actuation signal, the suction of the charging pumps is diverted from the volume control tank to the refueling water storage tank. The valves
isolating the boron injection tank from the centrifugal charging pumps and the
valves isolating the boron injection tank from the injection header then automatically open. The centrifugal charging pumps then inject RWST boric acid solution into the cold leg of each loop. The safety injection pumps also start automatically but provide no flow when the reactor coolant system (RCS) is at
normal pressure. The passive, accumulator safety injection system and the low
head, residual heat removal system also provide no flow at normal RCS pressure. A safety injection signal (SIS) normally results in a reactor trip followed by a turbine trip. However, it cannot be assumed that any single fault that actuates ECCS will also produce a reactor trip. If a reactor trip is generated
by the spurious SIS, the operator should determine if the spurious signal was transient or steady state in nature. The operator must also determine if the SIS should be blocked. For a spurious occurrence, the operator 15.5-1 Rev. 4 WOLF CREEK would terminate ECCS and maintain the plant in the hot shutdown condition. If the ECCS actuation instrumentation must be repaired, subsequent plant operation
would be in accordance with the Technical Specifications. If the reactor protection system does not produce an immediate trip as a result of the spurious SIS, the reactor experiences a negative reactivity excursion due to the injected boron, causing a decrease in reactor power. The power
mismatch causes a drop in Tavg and consequent coolant shrinkage. The pressurizer pressure and water level decrease. Load will decrease due to the
effect of reduced steam pressure on load after the turbine throttle valve is fully open. If automatic rod control is used, these effects will be lessened until the rods have moved out of the core. The transient is eventually terminated by the reactor protection system low pressurizer pressure trip or by
manual reactor trip. The time to trip is affected by initial operating conditions, including core burnup history, which affects initial boron concentration, rate of change of boron concentration, Doppler, and moderator coefficients. Recovery from the no reactor trip case is made in the same manner as described for the case where the SIS results directly in a reactor trip. The only difference is the lower Tavg and RCS pressure associated with the power
mismatch during the transient. The time at which reactor trip occurs is of no concern for this transient. At lower loads, coolant contraction will be slower, resulting in a longer time to trip. 15.5.1.2 Analysis of Effects and Consequences Method of Analysis The spurious operation of the ECCS is analyzed by employing the detailed digital computer program RETRAN02 (Ref. 3). The code simulates the neutron kinetics, RCS, pressurizer, pressurizer relief and safety valves, pressurizer spray, steam generator, steam generator safety valves, and the effect of the SIS. The program computes pertinent plant variables, including temperatures, pressures, and power level. Based on its expected frequency of occurrence, the inadvertent ECCS actuation at power is considered to be a Condition II event, a fault of moderate frequency. The specific criteria established for Condition II events include the following: a. Pressure in the reactor coolant and main steam systems should be maintained below 110% of the design values, b. Fuel cladding integrity shall be maintained by ensuring that the minimum DNBR remains above the 95/95 DNBR limit for PWRs, c. An incident of moderate frequency should not generate a more serious plant condition without other faults occurring independently. With respect to overpressurization, the inadvertent ECCS actuation at power event is bounded by the Loss of Load/Turbine trip events, in which assumptions are made to conservatively calculate the RCS and main steam system pressure transients. For the inadvertent ECCS actuation at power event, turbine trip occurs following reactor trip, whereas for the Loss of Load/Turbine Trip event, the turbine trip is the initiating fault. Therefore, the primary to secondary power mismatch and resultant RCS and main steam system heatup and pressurization transient are always more severe for the Loss of Load/Turbine Trip event. For this reason, it is not necessary to calculate the maximum RCS or main steam system pressure for the inadvertent ECCS actuation at power. 15.5-2 Rev. 17 WOLF CREEK Based on historical precedence, the inadvertent ECCS actuation at power event does not lead to a serious challenge of the DNB design basis. The decrease in core power and RCS average temperature more than offset the decrease in RCS pressure such that the minimum calculated DNBR occurs at the start of the transient. As such, no explicit analysis of the event has been performed to DNB concerns. The primary concern that results from an inadvertent actuation of the ECCS at power is that associated with pressurizer overfill. The pressurizer water volume increases as a result of the safety injection flow. This may eventually lead to filling of the pressurizer and subsequent water relief through the safety or relief valves. The passing of liquid through the pressurizer safety or relief valves could result in rupture of the pressurizer relief tank rupture disks, spilling radioactive coolant into the containment building, thereby escalating a Condition II event to a Condition III or IV event. Historically, Criterion c has been shown to be met by demonstrating that the pressurizer will not become water-solid. To prevent the pressurizer from becoming water-solid, operator action is ultimately required to terminate safety injection or mitigate the consequences of this event. Therefore, the event is analyzed to demonstrate that sufficient time is available for the appropriate operator actions to be taken to prevent filling the pressurizer. A bounding pressurizer overfill transient is presented representing maximum reactivity feedback. For calculational simplicity, zero injection line purge volume was assumed in this analysis, thus the boration transient begins
immediately when the appropriate valves are opened. Plant characteristics and initial conditions are further discussed in Section 15.0.3. The assumptions are as follows:
- a. Initial operating conditions Initial conditions with maximum uncertainties on power (+2%, vessel average temperature (-6.5°F), and pressurizer pressure (-30 psi) are assumed. The lower initial temperature results in a higher RCS coolant mass, causing a more severe pressurizer water volume transient.
- b. Reactivity feedback A large (absolute value) negative moderator temperature coefficient and a most-negative Doppler power coefficient are assumed.
- c. Reactor control The reactor was assumed to trip at the time of the SI signal.
Thus, the reactor control mode is of no consequence.
- d. Pressurizer heaters Pressurizer heaters are assumed to be inoperable. This assumption yields a higher rate of pressure drop.
- e. Boron Injection At the initiation of the event, two ECCS centrifugal charging pumps (CCPs) and a normal charging pump (NCP) inject RWST boron solution into the cold leg of each loop. 15.5-3 Rev. 17 WOLF CREEK
- f. Turbine load The reactor and turbine both trip at the time of SI actuation with
the turbine load dropping to zero simultaneously with the steam
flow. g. ECCS injection flowrates 105% of the maximum safeguards ECCS flow is delivered from two CCPs, plus flow from a NCP used for normal charging prior to the
occurrence of SI signal. All letdown is assumed isolated at the
initiation of the event. h. Reactor Trip An immediate reactor trip on the initiating SI signal to maximize pressurizer inventory is assumed. i. Operator Action to terminate SI The operator would take necessary action to terminate the safety injection flow within 8 minutes following event initiation. The
reduced operator action time is required to preclude the
possibility of a pressurizer water-solid condition and is supported
by plant operations through use of an emergency operating
procedure.
Major plant systems and equipment available for mitigation of transient and accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6. The actual parameters assumed and results are given in the respective
section/subsection. Table 15.0-6 incorporates events shown in the sequence
diagram, Figure 15.0-22. No single active failure in any of these systems or
equipment will adversely offset the consequences of the accident.
Results The calculated sequence of events is shown on Table 15.5-1.
Figures 15.5-1 through 15.5-3 show the transient response to inadvertent operation of ECCS during power operation.
Reactor trip occurs at event initiation followed by a rapid cooldown of the
RCS. Coolant contraction due to the decrease in reactor power and RCS
temperature results in a short-term reduction in pressurizer pressure and water
level. The temperature drop is mainly caused by the decrease in power but is
also affected by the addition of the cold SI flow. The combination of the RCS
heatup, due to residual heat generation, and ECCS injected flow causes the
pressure and level transients to rapidly turn around. Pressurizer water level
then increases steadily and reaches the peak water volume of 1789 ft 3 shortly after the ECCS flow is terminated. The pressurizer does not reach a water-solid condition, and hence, no water relief occurs through the pressurizer
safety or relief valves.
Recovery from this accident is discussed in Section 15.5.1.1.
15.5.1.3 Conclusions Results of the analysis show that the spurious ECCS operation with immediate
reactor trip meets all acceptance criteria for an ANS Condition II event.
If the reactor does not trip immediately, the low pressurizer pressure reactor
trip will be actuated. This trips the turbine and prevents excess cooldown, thereby expediting recovery from the incident.
15.5-4 Rev. 25 WOLF CREEK 15.5.2 CHEMICAL AND VOLUME CONTROL SYSTEM MALFUNCTION THAT INCREASES REACTOR COOLANT INVENTORY 15.5.2.1 Identification of Causes and Accident Description Increases in reactor coolant inventory caused by the chemical and volume control system may be postulated to result from operator error or a false
electrical signal. Transients examined in this section are characterized by increasing pressurizer level, increasing pressurizer pressure, and constant boron concentration. The transients analyzed in this section are done to demonstrate that there is adequate time for the operator to take corrective action to prevent filling the pressurizer.
An increase in reactor coolant inventory, which results from the addition of cold, unborated water to the RCS, is analyzed in Section 15.4.6, CHEMICAL AND VOLUME CONTROL SYSTEM MALFUNCTION THAT RESULTS IN A DECREASE IN BORON
CONCENTRATION IN THE REACTOR COOLANT. An increase in reactor coolant inventory which results from the injection of highly borated water into the RCS is analyzed in Section 15.5.1, INADVERTENT OPERATION OF THE EMERGENCY CORE COOLING
SYSTEM DURING POWER OPERATION. Transients postulated as a result of operator error or failure of the charging pump controller which increase primary side inventory will be automatically terminated by a high pressurizer level reactor trip before the pressurizer can be filled, thus these are not the worst cases. The most limiting case would result if charging was in automatic control and the pressurizer level channel being used for charging control failed in a low
direction. This would cause maximum charging flow to be delivered to the RCS and letdown flow would be isolated. The worst single failure for this event
would be another pressurizer level channel failing in an as is condition or a
low condition. This will defeat the reactor trip on two out of three high pressurizer level channels. To prevent filling the pressurizer the operator
must be relied upon to terminate charging. 15.5.2.2 Analysis of Effects and Consequences Method of Analysis The charging malfunction is analyzed by employing the detailed digital computer program LOFTRAN (Ref. 1). The code simulates the neutron kinetics, RCS, pressurizer, pressurizer relief and safety valves, pressurizer spray, steam
generator, steam generator safety valves, and the effect of the SIS. The
program computes pertinent plant variables, including temperatures, pressures, and power level. Four cases were analyzed;
- a. Minimum reactivity feedback with automatic pressurizer spray 15.5-5 Rev. 17 WOLF CREEK
- b. Minimum reactivity feedback without automatic pressurizer spray
- c. Maximum reactivity feedback with automatic pressurizer spray
- d. Maximum reactivity feedback without automatic pressurizer spray The assumptions incorporated in the analyses were as follows;
- a. Initial Operating Conditions The initial reactor power, RCS temperature, RCS pressure, and pressurizer level are assumed at their nominal values consistent with steady state full power operation
to perform an SCD analysis.
- b. Reactivity Coefficients
- 1. Minimum Reactivity Feedback Case
A most positive moderator temperature coefficient and a least negative Doppler-only power coefficient.
- 2. Maximum Reactivity Feedback Case A conservatively large negative moderator temperature coefficient and a most negative Doppler-only power
coefficient.
- c. Reactor Control A conservative analysis is performed assuming the reactor is in manual control. d. Charging System Maximum charging system flow based on RCS back pressure from one centrifugal charging pump is delivered to the
RCS. The charging flow is assumed to have the same boron concentration as the RCS.
- e. Reactor Trip
The transient is initiated by the pressurizer level channel which is used for control purposes failing low. As a worst single failure, another pressurizer level channel fails low, defeating the two out of three high
pressurizer level trip. Reactor trip on low pressurizer pressure is modeled in the cases presented herein. 15.5-6 Rev. 12 WOLF CREEK Results Figures 15.5-4 through 15.5-11 show the transient response due to the charging system malfunction. In the analyzed cases which model maximum reactivity feedback, core power and RCS average temperature remain relatively constant. In the cases which model minimum reactivity feedback, the core power initially decreases resulting in a reduction in RCS average temperature and pressure. A reactor trip ultimately occurs on low pressurizer pressure. Cases where the pressurizer spray is inoperable show the pressurizer level
increases at a relatively constant rate (following reactor trip for the minimum feedback case). This is because the pressurizer pressure initially rises very quickly to the pressure at which the relief valves open and remains there. Cases where the pressurizer spray is operable show the pressurizer level increases with varying rates. Spray actuation tends to keep the pressurizer pressure lower for several minutes, which allows the charging pumps to deliver more flow. Eventually, pressurizer pressure does increase enough to open the
relief valves. Times at which the operator would receive alarms are listed in Table 15.5-1.
15.5.2.3 Conclusions Results show none of the operating conditions during the transient approach core limits. The high pressurizer level trip has been defeated by failures, however, reactor trip on low pressurizer pressure occurs in some analyzed cases. The transient is ultimately terminated by the plant operators by isolating the ECCS injection and, thereby, terminating the pressurizer in-surge. The sequence of events presented in Table 15.5-1 show that the operators have sufficient time to take action necessary to prevent a pressurizer water-solid condition. 15.5.3 A NUMBER OF BWR TRANSIENTS
This section is not applicable to WCGS.
15.
5.4 REFERENCES
- 1. Burnett, T. W. T., et al., "LOFTRAN Code Description," WCAP-7907A, April 1984. 2. Stewart, C. W., et. al.,"VIPRE-01: A Thermal-Hydraulic Code for Reactor Cores," Battelle, Pacific Northwest Laboratories, EPRI NP-2511-CCM-A, August 1989. 3. McFadden, J. H., et. Al., RETRAN A Program for Transient Thermal Hydraulic Analysis of Complex Fluid Flow Systems, EPRI NP-1850-CCM-A, October 1984. 4. WCAP-11397-P-A, "Revised Thermal Design Procedure," A. J. Fiedland, et al., April 1989.
15.5-7 Rev. 12 WOLF CREEK TABLE 15.5-1 TIME SEQUENCE OF EVENTS FOR INCIDENTS WHICH RESULT IN AN INCREASE IN REACTOR COOLANT INVENTORY Accident Event Time (sec)Inadvertent actuation of ECC S injection begins 0.0 The ECC S during power Operation Control rod motion begins 2.0 (actuated on S I signal) Peak Pressurizer pressure 17.5 occurs AFW flow delivered to four 392 steam generators S afety injection flow 480 terminated (operator action) Peak pressurizer water ~600 volume occurs Chemical and volume Two pressurizer level 0.0 control system malfunc- channels fail low tion, minimum reactivity feedback, without pres- Maximum charging flow 0.0 surizer spray from one centrifugal charging pump is begun Letdown is isolated 0.0 Lo-lo pressurizer level alarm 0.0 Pressurizer relief 358. valve setpoint reached Hi pressurizer level 1388. alarm from the one working level channel Pressurizer fills 1572. Rev. 17 WOLF CREEK TABLE 15.5-1 (S heet 2) Accident Event Time (sec)Chemical and volume Two pressurizer level 0.0 control system mal- channels fail low function, minimum reac- tivity feed-back, with Maximum charging flow 0.0 pressurizer spray from one centrifugal charging pump is begun Letdown is isolated 0.0 Lo-lo pressurizer level 0.0 alarm Hi pressurizer level 1490. alarm from the one working level channel Pressurizer relief 1712. valve setpoint reached Chemical and volume Two pressurizer level 0.0 control system mal- channels fail low function, maximum reac-tivity feed-back, with- Maximum charging flow 0.0 out pressurizer spray from one centrifugal charging pump is begun Letdown is isolated 0.0 Lo-lo pressurizer level 0.0 alarm Pressurizer relief 77. valve setpoint reached Hi pressurizer level 1468. alarm from the one working level channel Pressurizer fills 1766. Rev. 7 WOLF CREEK TABLE 15.5-1 (S heet 3) Time Accident Event (sec)Chemical and volume Two pressurizer level
0.0 control
system mal-channels fail low function, maximum reac-tivity feed-back, with Maximum charging flow
0.0 pressurizer
spray from one centrifugal charging pump is begun Letdown is isolated 0.0 Lo-lo pressurizer level
0.0 alarm
Hi pressurizer level 916. alarm from the one working level channel Pressurizer relief 1400. valve setpoint reached Pressurizer fills 1704. Rev. 7 0.00.20.40.6 0.81.01.20100200300400500600Time (sec) Power (%)540 550 560 570 580 590 6000100200300400500600Time (sec) Temperature (F) Rev. 17 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.5-1 INADVERTENT OPERATION OF ECCS DURING POWER OPERATION 200 400 600 8001,0001,2001,400 1,600 1,800 2,0000100200300400500600Time (sec) Pressurizer Volume (ft 3)1,7001,800 1,9002,0002,1002,2002,300 2,4000100200300400500600Time (sec) Pressurizer Pressure (psia) Rev. 17 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.5-2 INADVERTENT OPERATION OF ECCS DURING POWER OPERATION 0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000100200300400500600Time (sec) Steam Flow (lbm/sec) 0 10 20 30 40 50 600100200300400500600Time (sec) ECCS Injection Flow (lbm/sec) Rev. 17 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.5-3 INADVERTENT OPERATION OF ECCS DURING POWER OPERATION r WOLF 2.,340 !:
- a.Do i 2,300 a.aaa 2,240 z,ooo ,---------------------------, 1,0oo
.. TIM£ (SECONDS) Rev. 7 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.5-4 CHEMICAL AND VOLUME CONTROL SYSTEM MALFUNCTION MAXIMUM REACTIVITY FEEDBACK WITH PRESSURIZER SPRAY 1.2 to I , .. b o.a t ..... I o .* : a.a,. 00 1500 'G:' auo -v i ... -1540 I S20 to-'" eooo WOLF CRUX I aoo aaa 1.000 1.800 I ,.ooo 1,800 T1ME (SECONDS) Rev. 7 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE. 15,5-5 CHEMICAL. AND VOLUME CONTROL SYSTEM MALFUNCTION MAXIMUM REACTIVITY FEEDBACK WitH PRESSURIZER SPRAY 2.3&0 .. I -2,340 r .... 2,300 1-.m . 2.210 2.2400 _I I -* 800 1.000 1.500 ,,eoo,-------------------------, *i' 1 * .00 1 ,.700 1'*.00 = 1.800
- 1.400 1::: 1' 100
'TIWC (D:COND.) Rev. 7 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.5 .. 6 CHEMICAL AND VOLUME CON'l'R.OL SYSTEM MALFUNCTION MAXIMUM REACTIVITY FEEDBACK WITHOUT PRESSURIZER SPl\AY ..
- G WOLF CAE£Jc 1.2 f* iu* 10.4 I 0.2 00 I l sao 1.CH)O 1.800 Tit<< (-CDNDa) Rev.* 1 WOLF CREEK UPDATED SAFETY ANALYSIS REPOaT FIGURE.lS.S-7 CHEMICAL AND VOLUME CONTROL SYSTEM MALFUNCTION MAXIMUM P.EAC1'IVITY FEEDBACK WITHOUT PRESSURIZER SPRAY
. woLP euzx 1,1100 ....... ----...... ....... --... 2,000.----------------------------., i 1,800 1 1.100 - 1,200 I 1.000 aoo i eoo ....... ----...... 500 1,000 1,5DO Tlt.IE (SECONDS) Rev. 7 WOLF CREEK UPnATED SAFETY ANALYSIS REPORT FIGURE 15.5.;.8 CHEMICAL AND VOLUME CONTROL SYSTEM MALFUNCTION MINIMUM REACTIVITY FEEDBACK WITH PRESSURIZEa SPRAY !.;
- I a2o Tlto4E (SECONDS) ltev. '7 WOLF CltEEK UPDA'l'ED SAFETY ANALYSIS REPORT FIGURE' 15.5-9 CHEMICAL AND VOLUME CONTR.OL SYSTEM MALFUNCTION MINIMUM REACTIVITY FEEDBACK WITH PRESSURIZER SPRAY 2.400 2,300 I I 2,.200 12,100 1**-, ** oo
....... ! 1,800 I UIOO -.1.400 ; 1,200 m I 1,ooo I 800 1!100 Rev. 7 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE CHEMICAL AND VOLUME CONTROL SYSTEM MALFUNCTION MINIMUM REACTIVITY FEEDBACK WI'l'BOUT PRESSURIZER SPRAY 0 WOLF CREEK 1.2 ?, r\ o.e i 0.0 t-i 0.4 t-0.2 -z Q 0 500 1,000 1,500 TIME (SECONDS) Rev 7 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.5-11 CHEMICAL AND VOLUME CONTROL SYSTEM MALFUNCTION MINIMUM REACTIVITY FEEDBACK WITHOUT PRESSURIZER SPRAY WOLF CREEK 15.6 DECREASE IN REACTOR COOLANT INVENTORY
Events which result in a decrease in reactor coolant inventory, as discussed in
this section, are as follows:
- a. Inadvertent opening of a pressurizer safety or relief
valve
- b. Break in instrument line or other lines from the reactor
coolant pressure boundary that penetrate the containment
- c. Steam generator tube rupture (SGTR)
- d. Spectrum of boiling water reactor (BWR) steam system
piping failures outside of the containment (Not
applicable to WCGS)
- e. Loss-of-coolant accident (LOCA) resulting from a spectrum
of postulated piping breaks within the reactor coolant
pressure boundary
- f. A number of BWR transients (Not applicable to WCGS)
All of the applicable accidents in this category have been analyzed. It has
been determined that the most severe radiological consequences will result from
the major LOCA of Section 15.6.5. Therefore, the LOCA is the design basis
accident. The LOCA CVCS letdown line break outside the containment and the SGTR
accident have been analyzed radiologically. All other accidents in this
section are bounded by these accidents.
15.6.1 INADVERTENT OPENING OF A PRESSURIZER SAFETY OR RELIEF
VALVE
15.6.1.1 Identification of Causes and Accident Description
An accidental depressurization of the reactor coolant system (RCS) could occur
as a result of an inadvertent opening of a pressurizer relief or safety valve.
Since a safety valve is sized to relieve approximately twice the steam flow
rate of a relief valve, and will therefore allow a much more rapid
depressurization upon opening, the most severe core conditions resulting from
an accidental depressurization of the RCS are associated with an inadvertent
opening of a pressurizer safety valve. Initially, the event results in a
rapidly decreasing RCS pressure until this pressure reaches a value
corresponding to the hot leg saturation pressure. At this time, the rate of
pressure decrease is reduced considerably. The pressure continues to decrease
throughout the transient. The effect of the pressure decrease would be to
15.6-1 Rev. 0 WOLF CREEK decrease power via the moderator density feedback, but the reactor control system (if in the automatic mode) functions to maintain the power essentially
constant throughout the initial stage of the transient. The average coolant
temperature decreases slowly, but the pressurizer level increases until reactor
trip.
The reactor may be tripped by the following reactor protection system signals:
- a. Overtemperature T b. Pressurizer low pressure
An inadvertent opening of a pressurizer safety or relief valve is classified as
an ANS Condition II event, a fault of moderate frequency. See Section 15.0.1
for a discussion of Condition II events.
15.6.1.2 Analysis of Effects and Consequences
Method of Analysis The inadvertent opening of a pressurizer safety valve transient is analyzed by employing the detailed digital computer program RETRAN-02 (Ref 3 in section 15.6.3.5). RETRAN-02 has been found acceptable by the NRC for use as a licensing basis safety analysis code. RETRAN-02 is a thermal-hydraulic systems
analysis code employing a one-dimensional, homogeneous equilibrium mixture
thermal-hydraulic model for the RCS, a point kinetics model for the reactor
core, special component and auxiliary models (ex., pumps, temperature
transport, non-equilibrium pressurizer) and control system models. The code
computes pertinent plant transient information including core power level, RCS
pressure and temperature. VIPRE-01 (Ref 5 in section 15.6.3.5) is used to evaluate the core thermal limits to determine DNBR. RETRAN-02 generated state
points are used as VIPRE-01 boundary conditions to perform a Statistical Core
Design (SCD) DNB analysis.
Plant characteristics and initial conditions are discussed in Section 15.0.3.
In order to give conservative results in calculating the departure from
nucleate boiling ratio (DNBR) during the transient, the following assumptions
are made:
- a. Initial conditions of nominal core power, reactor
coolant temperatures, and reactor coolant pressure
are assumed to perform an SCD DNB analysis (see
Section 15.0.3).
- b. A most positive moderator temperature coefficient of
reactivity is assumed. The spatial effect of the void
due to local or subcooled boiling, which tends to flatten
the core power distribution, is not considered in the
analysis with respect to reactivity feedback or core
power shape.
- c. A large (absolute value) Doppler coefficient of
reactivity such that the resultant amount of positive
feedback is conservatively high to retard any power
decrease due to moderator reactivity feedback.
15.6-2 Rev. 13 WOLF CREEK Major plant systems and equipment available for mitigation of transient and accident conditions which may be required to function to mitigate the effects of RCS depressurization caused by inadvertent safety valve opening are discussed in Section 15.0.8 and listed in Table 15.0-6. The actual parameters assumed and results are given in the respective section/subsection. Table 15.0-6 incorporates events shown in the sequence diagram, Figure 15.0-23. Normal reactor control systems are not required to function. The rod control
system is assumed to be in the automatic mode in order to hold the core at full
power longer and thus delay the trip. This is a worst case assumption; if the
reactor were in manual control, a trip could occur earlier on overtemperature
DT or low pressurizer pressure. The reactor protection system functions to
trip the reactor on the appropriate signal. No single active failure will
prevent the reactor protection system from functioning properly.
Results The system response to an inadvertent opening of a pressurizer safety valve is
shown on Figures 15.6-1 and 15.6-2. Figure 15.6-1 illustrates the nuclear
power transient following the depressurization. Nuclear power is maintained at
the initial value until reactor trip occurs on overtemperature DT. The
pressure decay transient and average temperature transient following the
accident are given in Figure 15.6-1. Pressure drops more rapidly when core
heat generation is reduced via the trip, and then slows once saturation
temperature is reached in the hot leg. The DNBR decreases initially, but
increases rapidly following the trip, as shown in Figure 15.6-2. The DNBR
remains above the safety analysis limit throughout the transient. The DNBR
design basis is described in Section 4.4.
The calculated sequence of events for the inadvertent opening of a pressurizer
safety or relief valve incident is shown on Table 15.6-1.
15.6.1.3 Conclusions
The results of the analysis show that the pressurizer low pressure and the
overtemperature DT reactor protection system signals provide adequate
protection against the RCS depressurization event.
15.6.2 BREAK IN INSTRUMENT LINE OR OTHER LINES FROM REACTOR
COOLANT PRESSURE BOUNDARY THAT PENETRATE CONTAINMENT
There are no instrument lines connected to the RCS that penetrate the
containment. There are, however, the grab sample lines from the hot legs of
reactor coolant loops 1 and 3, from the steam and liquid space of the
pressurizer, and from the 3-inch chemical and
15.6-3 Rev. 13 WOLF CREEK volume control system letdown line penetrating the containment. The grab sample lines are provided with normal closed isolation valves on both sides of the
containment wall and are designed in accordance with the requirements of GDC-
- 55.
The most severe pipe rupture with regard to radioactivity release during normal
plant operation is rupture of the chemical and volume control system letdown
line at a point outside of the containment. For such a break, the reactor
coolant letdown flow would have passed sequentially from the cold leg and
through the regenerative heat exchanger and letdown orifices. The letdown
orifice reduces the letdown line pressure from 2,235 psig to less than 600 psig
outside containment during normal plant operation when letdown flow is
maintained at a nominal 120 gpm. Increase in flow will occur due to a rupture of the letdown line downstream of the orifices. It has been determined that
the occurrence of a complete severance of the letdown line would result in a
loss of reactor coolant at the rate of 222 gpm.
Since the reactor makeup water transfer pumps are designed to deliver 120 gpm
to the boric acid blending tee, the capability of the reactor makeup system can
not maintain VCT level. The imbalance of the VCT outflow and inflow would
eventually result in water level dropping to VCT level Lo/Refueling Water
Sequence setpoint (5%) and the suction of the charging pump would automatically
be shifted from the VCT to the RWST. In addition, the calculated releases rate
is beyond the capacity of a single charging pump, which is capable of
delivering 150 gpm flow to the RCS under normal operating conditions, if the
RCP seal leakoff and any identified leakage are accounted for. The control
room operators would be alerted of the failure by a high charging flow alarm
and/or continuous VCT makeup and a slowly decreasing VCT and pressurizer level.
The high charging flow alarm procedure in conjunction with the plant off-normal
procedure for high RCS leakage would require letdown isolation inside the
containment which would terminate the coolant loss.
15.6.2.1 Radiological Consequences
15.6.2.1.1 Method of Analysis
15.6.2.1.1.1 Physical Model
The volatile fractions of the spilled reactor coolant are assumed to be
available for immediate release to the environment.
15.6.2.1.1.2 Assumptions and Conditions
The major assumptions and parameters used in the analysis are provided in Table
15.6-2 and summarized below:
- a. The reactor coolant iodine activity is based on the dose equivalent of 1.0 Ci/gm of I-131.
- b. The noble gas activity in the reactor coolant is based on 1-percent failed fuel.
- c. A total of 111,600 pounds of reactor coolant is spilled onto the floor of the auxiliary building. (Based on doubling the maximum flowrate of 222 gpm to account for backflow over a thirty minute release, followed by a ten second valve closure period).
- d. All of the noble gases in the spilled reactor coolant are released to the environment.
15.6-4 Rev. 25 WOLF CREEK
- e. Ten percent of the spill is assumed to flash. All of the iodine activity in the flashed fraction of the spill is
assumed to be released.
- f. No credit is taken for mixing and holdup of the releases
within the auxiliary building, nor are the auxiliary
building normal exhaust filters credited with reducing
the release. That is, the release is modeled as being
direct to the environment.
15.6.2.1.1.3 Mathematical Models Used in the Analysis
Mathematical models used in the analysis are described in the following
sections:
- a. The mathematical models used to analyze the activity
released during the course of the accident are described
in Appendix 15A.
- b. The atmospheric dispersion factors used in the analysis
were calculated based on the onsite meteorological
measurement programs described in Section 2.3 and provided in Table 15A-2.
- c. The thyroid inhalation and total body immersion doses to
a receptor at the exclusion area boundary or outer
boundary of the low-population zone were analyzed, using
the models described in Appendix 15A.
15.6.2.1.1.4 Identification of Leakage Pathways and Resultant
Leakage Activity
The reactor coolant spilled in the auxiliary building will collect in the floor
drain sumps. From there, it will be pumped to the radwaste treatment system.
Therefore, the only release paths that present a radiological hazard involve
the volatile fraction of spilled coolant.
Normally, gases released in the auxiliary building mix with the building
atmosphere and are gradually exhausted through the filtered building
ventilation system. The charcoal filters normally remove a very large fraction
of the airborne iodine in the building atmosphere. However, the ventilation
system is not designed to mitigate the consequences of an accident (e.g., it
might not survive an earthquake more severe than the operating-basis
earthquake), nor can the possibility of unplanned leakages from the auxiliary
building be eliminated; hence, no credit is taken for these effects reducing
the released activity.
15.6-5 Rev. 1 WOLF CREEK The evaporated radionuclides are assumed to be available immediately to the outside atmosphere. This activity is tabulated in Table 15.6-2.
15.6.2.1.2 Identification of Uncertainties and Conservatisms in
the Analysis
The principal uncertainties in the calculation of doses following a letdown
line rupture arise from the unknown extent of reactor coolant contamination by
radionuclides, the quantity of coolant spilled, the fraction of the spilled
activity that escapes the auxiliary building, and the environmental conditions
at the time. Each of these uncertainties is treated by taking worst-case or
extremely conservative assumptions.
The extent of coolant contamination assumed greatly exceeds the levels expected
in practice. The rupture is postulated in a seismic Category I, ASME Section
III, Class 2 piping system. It is assumed that the leak goes undetected for 30
minutes. It is expected that considerable holdup and filtration occurs in the
auxiliary building, but no credit is assumed.
The purpose of all these conservatisms is to place an upper bound on doses.
15.6.2.1.3 Conclusions
15.6.2.1.3.1 Filter Loadings
No filter is credited with the collection of radionuclides in this accident
analysis. The buildup on these filters (auxiliary building and control
building charcoal filters) that may be expected due to the adsorption of some
of the iodine is very small compared with the design capacity of these filters.
15.6.2.1.3.2 Dose to Receptor at the Exclusion Area Boundary and
Low-Population Zone Outer Boundary
The radiological consequences resulting from the occurrence of a postulated
letdown line rupture have been conservatively analyzed, using assumptions and
models described in previous sections.
The thyroid inhalation total-body immersion doses have been analyzed for the 0-
2 hour dose at the exclusion area boundary and for the duration of the accident
at the low-population zone outer boundary. The results are listed in Table
15.6-3. The resultant doses are within a small fraction of the guideline values
of 10 CFR 100.
15.6.3 STEAM GENERATOR TUBE RUPTURE (SGTR) The steam generator tube rupture (SGTR) examined is the complete severance of one single steam generator tube which results in the leakage of reactor coolant into the secondary side of the steam generator. The consequences of SGTR depend largely upon the ability of the operator to take the necessary actions to terminate the primary to secondary leakage. If the leakage continues for an extended period of time, the secondary side of the steam generator may become filled and water may enter the steamline. As a result, the release of liquid through the secondary side safety/relief valves to the atmosphere may occur that could result in an increase in the radiological doses.
Two SGTR scenarios are evaluated in order to ensure that operators can respond to the accident in a timely manner so as to minimize the resulting offsite releases and prevent overfilling of the effected steam line. Those scenarios are described below:
15.6-6 Rev. 22 WOLF CREEK Overfill Scenario: The overfill SGTR scenario assumes failures in the auxiliary feedwater (AFW) system such that if operators do not respond quickly enough to terminate feedwater, then the affected steam line may fill with water. The specific failure involves the control valve on the discharge side of the motor driven feedwater pump feeding the faulted steam generator. To maximize flow to the faulted steam generator, it is assumed that this valve fails in the wide-open position. Failure of this valve, coupled with the contribution from the turbine driven AFW pump, has the potential for overfilling the faulted steam generator and subsequently, relieve water via a safety valve. The radionuclide releases are maximized by a assuming the safety valve is stuck-open following water relief, with an effective flow area equal to 5% of the total safety valve flow area. Stuck-open ARV Scenario: The stuck-open ARV scenario assumes that when the faulted steam generator's atmospheric relief valve (ARV) is initially required to open, that it remains stuck open for 21.53 minutes. The basis for this time period includes consideration of the time the valve is stuck open until the time that an operator manually closes the associated block valve. Failure of the faulted steam generator's ARV thus maximizes offsite release by assuming a direct path to the atmosphere. The above cases are considered to be ANS Condition IV events, a limiting fault (USAR Section 15.0.1). It has been determined that the most severe
radiological consequences will result from the forced steam generator overfill
scenario with a stuck-open safety valve (Reference 2). Therefore, the
radiological consequences are reported for that limiting case only.
Major plant systems and equipment available for mitigation of transient and
accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6.
The actual parameters assumed and results are given in the respective
section/subsection. Table 15.0-6 incorporates events shown in the sequence
diagram, Figure 15.0-24.
15.6.3.1 STEAM GENERATOR TUBE RUPTURE WITH FAILURE OF FAULTED
STEAM GENERATOR AFW CONTROL VALVE
15.6.3.1.1 Identification of Cause and Accident Description
The accident examined is the complete severance of a single steam generator
tube. The accident is assumed to take place at power with the reactor coolant
contaminated with fission products corresponding to continuous operation with a
limited number of defective fuel rods. The accident leads to an increase in
the contamination of the secondary system due to the leakage of radioactive
coolant from the RCS. Loss of off-site power is assumed to occur coincident
with reactor trip. Discharge of activity to the atmosphere takes place via the
steam generator safety and/or atmospheric relief valves.
In view of the fact that the steam generator tube material is Inconel-600 and
is a highly ductile material, the assumption of a complete severance is
conservative. The more probable mode of tube failure would be one or more
minor leaks of undetermined origin. Activity in the steam and power conversion
system is subject to continual surveillance, and an accumulation of minor leaks
which exceed the limits established in the Technical Specifications is not
permitted during the unit operation.
15.6-7 Rev. 22 WOLF CREEK Following the occurrence of the SG tube rupture, the primary to secondary
leakage causes the pressurizer level and the RCS pressure to decrease. As the
RCS pressure continues to decrease, automatic reactor trip occurs on low pressurizer pressure or over-temperature delta-T(OTT) signal. Because of the assumed loss of offsite power, the steam dump system will not be available, and the secondary side pressure increases rapidly after reactor trip until the steam generator ARVs and/or SV lift to dissipate the energy. After reactor trip, the RCS pressure continues to decrease and the safety injection is
automatically initiated on low pressurizer pressure signal. Due to the assumed
loss of offsite power at the reactor trip, normal feedwater flow is terminated
and the AFW is initiated.
The analysis assumes failure of the AFW control valve on the discharge side of
the motor-driven AFW pump feeding the ruptured steam generator. It is assumed
that this valve fails in the wide-open position to maximize the flow to the
ruptured steam generator. Failure of this valve coupled with the contribution
from the turbine-driven AFW pump has a greater potential for overfilling the
ruptured steam generator.
The operator is expected to determine that a SGTR has occurred and to identify
and isolate the ruptured steam generator on a restricted time scale to minimize
contamination of the secondary system and ensure termination of radioactive
release to the atmosphere from the ruptured steam generator. The recovery
procedure then can be carried out on a time scale to ensure that break flow to
the secondary system is terminated.
Consideration of the indications provided at the control board, together with
the magnitude of the break flow, leads to the conclusion that the accident
diagnostics and isolation procedure can be completed so that pressure
equalization between primary and secondary side of the ruptured steam generator
can be achieved to stop the break flow.
Assuming normal operation of the various plant control systems, the following
sequence of events is initiated by a design basis tube rupture:
- a. Pressurizer low pressure and low level alarms are activated and charging pump flow increases in an attempt to maintain pressurizer level. On the secondary side, there is a steam flow/feedwater flow mismatch before trip
as feedwater flow to the ruptured steam generator is reduced due to the additional break flow being supplied to that loop.
- b. Decrease in RCS pressure (Figure 15.6-3a) due to continued loss of reactor coolant inventory leads to a reactor trip signal generated by low
pressurizer pressure or over-temperature Delta T. It is conservatively
postulated that loss of offsite power (LOOP) occurs when the reactor trips.
15.6-8 Rev. 7 WOLF CREEK The LOOP signal initiates auxiliary feedwater addition. Resultant plant
cooldown (Figures 15.6-3b and 15.6-3c) following reactor trip leads to a rapid
change of pressurizer level (Figure 15.6-3f), and the safety injection signal, initiated by low pressurizer pressure, follows soon after the reactor trip.
With the loss of offsite power occurring at the reactor trip, normal feedwater
is terminated and the auxiliary feedwater is being supplied to the steam
generators.
- c. The steam generator blowdown liquid monitor alarm and/or the condenser air discharge radiation monitor alarm will activate, indicating a sharp
increase in radioactivity in the secondary system. The alarms
automatically cause termination of steam generator blowdown.
- d. The reactor trip automatically trips the turbine, and if offsite power is available the steam dump valves open, permitting steam dump to the
condenser. In the event of a coincident loss of offsite power, as assumed
in the transient presented in this section, the steam dump valves would
automatically close to protect the condenser. The steam generator pressure (Figure 15.6-3d) would rapidly increase, resulting in steam discharge to
the atmosphere through the steam generator safety/atmospheric relief
valves. In Figure 15.6-3g, the steam flow is constant initially until
reactor trip, followed by turbine trip, which results in a large decrease
in flow, but a rapid increase in steam pressure to the safety/relief valve
setpoints.
- e. Following reactor trip, the continued action of auxiliary feedwater supply and borated safety injection flow (supplied from the refueling water
storage tank) provide a heat sink which absorbs the decay heat.
- f. Safety injection flow results in increasing the pressurizer water level (Figure 15.6-3f); the rate of which depends upon the amount of operating
auxiliary equipment.
- g. Following water relief through the ruptured steam generator safety valve, the ruptured steam generator pressure is uncontrollably decreasing (Figure
15.6-3d) and the operator is directed to enter the Emergency Operating
Procedure EMG C-31.
15.6.3.1.2 Analysis of Effects and Consequences
Method of Analysis An analysis was performed to determine the thermal and hydraulic transient for a postulated SGTR, which results in steam generator overfill. The amount of primary to secondary leakage and the mass releases to the atmosphere from both the ruptured and intact steam generators were determined from the occurrence of the tube rupture to the second RCS depressurization following the switchover from the Emergency Operating Procedure EMG E-3 to EMG C-31. The SGTR recovery actions to cooldown and depressurize the plant to cold shutdown were also simulated in the analysis. The analysis was performed using the RETRAN-3D computer code (Reference 6), operating in the RETRAN-02 mode.
15.6-9 Rev. 22 WOLF CREEK In estimating the mass transfer from the RCS through the broken tube, the
following assumptions are made:
- a. Reactor trip occurs automatically as a result of low pressurizer or
overtemperature Delta T. Loss of offsite power occurs at reactor trip.
- b. Auxiliary feedwater flow rate is allowed to vary with the fluctuation in
the faulted steam generator pressure. This results in higher AFW flow when the
faulted steam generator pressure decreases. Eight minutes following the
initiation of the safety injection signal, the AFW from the turbine driven AFW
pump to the ruptured steam generator is terminated by closing the un-failed AL-
HV valve. Eighteen minutes following the initiation of the safety injection
signal, the AFW from the motor-driven AFW pump to the ruptured steam generator
is terminated by locally closing the failed AL-HV valve. AFW flow to the
intact steam generators maintains the narrow range level between 6% and 50% as indicated in the Emergency Operating Procedure EMG E-3.
- c. Cooldown of the RCS is initiated at 30 minutes following the initiation of
the safety injection signal. It is assumed that steam is released through the
remaining three operable steam generator ARVs in the intact loops until the RCS
temperature of the core exit thermal couples corresponds to the ruptured SG
pressure as listed in the EMG E-3 procedure. Note that the analysis assumes
that the operators will continue to maintain the plant at that temperature for
the duration of the transient, consistent with the EMG E-3 procedure.
Technical Specification LCO 3.7.4 requires that all four steam generator ARVs shall be operable. With one of the required ARVs unavailable due to its
association with the ruptured steam generator, the remaining three ARVs are
available to ensure that subcooling can be achieved for the RCS.
- d. Following termination of the RCS cooldown, the RCS is depressurized by
opening a pressurizer PORV to assure an adequate coolant inventory prior to
terminating SI flow. Primary depressurization is initiated at 8 minutes
following the termination of the RCS cooldown and continues until the RCS
pressure is less than the ruptured steam generator pressure.
- e. Following the depressurization, termination of SI is delayed to ensure
enough liquid enters the ruptured steam generator steamline to force the safety
valve open and cause water relief. It is assumed that 5 minutes following the
termination of the RCS depressurization that the safety injection flow is
reduced to just one centrifugal charging pump. At 15 minutes following the
termination of the RCS depressurization, the one CCP is throttled back to 100
gpm and at 30 minutes following termination, letdown is initiated such that the
net flow due to SI and letdown depressurization is zero.
15.6-10 Rev. 22 WOLF CREEK The above assumptions are conservatively made to increase the probability for
faulted steam generator overfill and to maximize the radioactive releases to
the atmosphere.
Key Recovery Sequence
The recovery sequence to be followed consists of the following major operator
actions:
- a. Identification of the faulted steam generator
- b. Isolation of the faulted steam generator
- c. Assuring subcooling of the RCS fluid to approximately 50°F below the
faulted steam generator temperature
- d. Depressurization of the RCS to a value equal to the faulted steam generator
pressure
- e. Subsequent termination of safety injection flow
- f. Further cooldown and depressurization of the RCS to conditions suitable for
RHR initiation
Results In Table 15.6-1, the sequence of event are presented. These events include
postulated operator response times and normal plant response to the normal
plant setpoints. Primary and secondary system parameters are plotted as a
function of time in Figures 15.6-3a through 15.6-3j.
It is important to note that only steam is released from the ruptured steam generator, prior to steam generator overfill. However, after overfill occurs, the releases from the ruptured steam generator may be water and/or steam depending upon the conditions in the steam generator. After the water and steam mixture is discharged through the safety valves, a consequential failure of the safety valve was assumed. With a failed-open safety valve on the ruptured steam generator, the ruptured steam generator will continue to depressurize (Figure 15.6-3d). Thus, primary and secondary pressure equalization can not be achieved, and the primary to secondary leakage and release to the atmosphere will continue until cold shutdown conditions are reached. As depicted in Figure 15.6-3j, the faulted steam generator fills at approximately 1910 seconds. As a result, the overfilled steam generator water starts to enter the main steam line on the faulted loop and water/vapor mixture relief through the ruptured steam generator safety valve occurs at approximately 2635 seconds. Eventually, the 682 ft 3 steam line will be filled with water at approximately 4175 seconds. It should be noted that the steam lines have been statically analyzed to withstand all steam lines being completely filled with water.
15.6-11 Rev. 22 WOLF CREEK 15.6.3.2 STEAM GENERATOR TUBE RUPTURE WITH POSTULATED STUCK-OPEN
ATMOSPHERIC RELIEF VALVE
15.6.3.2.1 Identification of Causes and Accident Description
The accident description for this SGTR is identical to that discussed in
Section 15.6.3.1.1 with the exception that the ARV for the faulted steam
generator is assumed to remain open for 20 minutes following initial secondary
pressure relief, shortly after reactor trip.
In this SGTR scenario, the operator is expected to determine that a SGTR has
occurred, to recognize the failure of the ARV, to dispatch personnel to
manually isolate the ARV, and then to isolate the affected steam generator. In
this accident the failure of the ARV allows a longer period for radionuclide
release than otherwise expected.
The accident involves the complete severance of a single steam generator tube
with Loss of Offsite Power coincident with reactor trip. For a discussion of
normal operation of plant control systems to a design basis SGTR refer to
Section 15.6.3.1.1.
15.6.3.2.2 Analysis of Effects and Consequences
Methods of Analysis
An analysis was performed to determine the thermal and hydraulic transient for a postulated SGTR, which assumes failure of the faulted steam generator's ARV. The amount of primary to secondary leakage and the mass releases to the atmosphere from both the ruptured and intact steam generators were determined from the occurrence of the tube rupture to the second RCS depressurization following the switchover from the Emergency Operating Procedure EMG E-3 to EMG C-31. The SGTR recovery actions to cooldown and depressurize the plant to cold shutdown were also simulated in the analysis. The analysis was performed using the RETRAN-3D computer code (Reference 6), operating in the RETRAN-02 mode.
In estimating the mass transfer from the RCS through the broken tube, the
following assumptions are made:
- a. Reactor trip occurs automatically as a result of low pressurizer pressure or overtemperature Delta T. Loss of offsite power occurs at reactor trip.
- b. As pressures rise on the secondary side, the steam generator atmospheric relief valves (ARVs) open to release excess secondary pressure. Although the ARVs in the unaffected steam generator close within 7 minutes, the ARV for the faulted steam generator is assumed to remain open and steam release to continue for 21.53 minutes until the ARV block valve is manually closed.
15.6-12 Rev. 22 WOLF CREEK
- c. AFW is initially delivered at a rate of 250 gpm to each steam generator. AFW is maintained to assure that narrow range level in each steam generator exceeds 15%.
- d. Following ruptured steam generator isolation, cooldown is initiated when the narrow range in the ruptured steam generator is greater than 10% and its pressure exceeds 630 psia. Cooldown continues until RCS temperature is reduced to 50°F less than the ruptured steam generator saturation temperature.
- e. Reactor coolant system depressurization is initiated
5.6 minutes
after completion of cooldown. This timing is consistent with observed simulator exercises.
- f. After primary side depressurization is completed and SI termination criteria are met, a 9.8 minute time delay is assumed prior to SI termination.
- g. Following SI termination, the operators equalize pressure in the RCS and faulted SG in 20 minutes. During this time break flow in the faulted SG continues. After pressures are equalized, it is conservatively assumed that the transition to cold shutdown is made utilizing steam release to the atmosphere from the faulted SG.
Key Recovery Sequence
The recovery sequence to be followed consists of the following major operator
actions:
- a. Identification of the faulted steam generator
- b. Identification and manual closure of the stuck-open atmospheric relief valve
- c. Isolation of the faulted steam generator
- d. Assuring subcooling of the RCS fluid to approximately 50°F below the faulted steam generator temperature
- e. Depressurization of the RCS to a value equal to the faulted steam generator pressure
- f. Subsequent termination of safety injection flow
- g. Further cooldown and depressurization of the RCS to conditions suitable for RHR initiation.
Results In Table 15.6-1, the sequence of events are presented. These events include postulated operator response times and normal plant responses to the normal plant setpoints. Primary and secondary system parameters are plotted as a function of time in Figures 15.6-3k through 15.6-3t.
15.6-13 Rev. 22 WOLF CREEK 15.6.3.3 Radiological Consequences 15.6.3 3.1 Method of Analysis
The analysis of the radiological consequences of an SGTR considers the most severe release of secondary activity, as well as primary system activity leaked from the tube break. The inventory of iodine and noble gas fission product activity available for release to the environment depends on the primary to secondary coolant leakage rate, the percentage of defective fuel in the core, and the mass of steam discharged to the environment. The re-analysis of the radiological consequences of a postulated SGTR uses the guidelines provided in Regulatory Guide 1.195 (Reference 7) for assumptions and methods to calculate the offsite dose consequences. This involved changing three elements of the analysis of record methodology (Reference 1):
(1) The reanalysis uses thyroid dose conversion factors (DCFs) for inhalation of radionuclides based on the data provided in Table 2.1 of Federal Guidance Report 11, "Limiting Values of Radionuclide Intake and Air Concentration and Dose Conversion Factors for Inhalation, Submersion, and Ingestion". This is a departure from the more conservative DCF values listed in Regulatory Guide 1.109, which were used in the previous analysis of record, (2) The effective dose conversion factors, provided in Table III.1 of Federal Guidance Report 12, "External Exposure to Radionuclides in Air, Water, and Soil", are used to calculate the whole body doses. This deviates from the previous analysis of record, which used the more conservative DCF values listed in Regulatory Guide 1.109, and (3) The reanalysis uses a factor of 335 for the accident initiated iodine spike release rate, which is a departure from the more conservative factor of 500 modeled in the previous analysis of record.
These methodology changes reduce the magnitude of the accident source term and result in lower doses than would be obtained using the methodology previously presented in the SGTR with overfill analysis of record. However, the Regulatory Guide 1.195 source term methodology is recognized by the nuclear industry as having a better scientific basis and has been approved by the NRC for the design and licensing applications.
15.6.3.3.1.1 Physical Model
The evaluation of the radiological consequences of a postulated steam generator
tube rupture (SGTR) utilizes the results of the RETRAN analyses to calculate
releases of radioactive iodines and noble gases to the atmosphere to the time
of RHR cut-in conditions.
Concentrations of radioactivity in the RCS water and in the faulted and intact
steam generators are calculated utilizing release rates from the fuel, calculated mass flows and conventionally used partitioning coefficients between
the liquid and steam phases. These radioactivity concentrations and the
calculated releases of mass to the atmosphere yield the released activity.
Radiological consequences are calculated using atmospheric dispersion coefficients, breathing rates, and other aspects of conventional radiological consequence calculations.
15.6.3.3.1.2 Assumptions and Conditions
The major assumptions and parameters assumed in the analysis are itemized in
Table 15.6-4 and 15A-1 and are summarized below.
15.6-14 Rev. 22 WOLF CREEK a. The assumed reactor coolant iodine activity is determined for the following two cases:
Case 1 - An initial reactor coolant iodine activity equal to the dose equivalent of 60.0 Ci/gm of I-131 due to a pre-accident iodine spike caused by RCS transients prior to the SGTR.
Case 2 - An initial reactor coolant iodine activity equal to the dose equivalent of 1.0 Ci/gm of I-131 with an iodine spike that increases the escape rate from the fuel into the coolant by a
factor of 335 immediately after the accident. This increased escape rate is assumed for the duration of the accident.
- b. The noble gas activity in the reactor coolant is based on 1-percent failed fuel as provided in Table 11.1-5.
- c. The initial secondary coolant activity is based on the dose equivalent of 0.1 mCi/gm of I-131.
The following assumptions and parameters are used to calculate the activity
released and the offsite dose following an SGTR:
- a. The amount of discharge or reactor coolant in the secondary system as a function of time is as calculated by RETRAN analysis.
The analysis yields 195,371 pounds of reactor coolant transferred to the secondary side of the faulted steam generator.
- b. It is assumed that all of the iodine in the fraction of reactor coolant that flashes to steam upon reaching the secondary side is
released to the steam phase. No credit is taken for scrubbing.
- c. A 1-gpm primary-to-secondary leak is assumed to occur to the unaffected steam generators, through the accident sequence.
- d. All noble gas activity in the reactor coolant that is transported to the secondary system via the tube rupture and the primary-to-
secondary leakage is released to the atmosphere.
- e. The iodine partition fraction between the liquid and steam in the steam generator is assumed to be 0.01.
- f. The steam releases from the steam generators to the atmosphere are as calculated by RETRAN analysis and given in Table 15.6-4. The
total faulted feedwater flows to all steam generators are also
listed in Table 15.6-4.
- g. Radioactivity releases to the atmosphere are based on the concentrations of radioactivity in the steam phase times the
calculated amounts of steam release.
- h. No additional radioactivity releases occur after the initiation of RHR system cooling.
- i. Radioactive decay prior to the release of activity is considered.
No decay during transit or ground deposition is considered.
- j. Short-term accident atmospheric dispersion factors, breathing rates, and dose conversion factors are provided in Tables 15A-2, 15A-1, and 15.6-4, respectively.
15.6-15 Rev. 22 WOLF CREEK 15.6.3.3.1.3 Mathematical Models Used in the Analysis
Mathematical models used in the analysis are described in the following
sections:
- a. The mathematical models used to analyze the activity released during the course of the accident are described in Reference 1 and
- 2. b. The atmospheric dispersion factors used in the analysis were calculated based on the onsite meteorological measurements program, as described in USAR Section 2.3, and are provided in Table 15A-2. c. The thyroid inhalation immersion doses to a receptor at the exclusion area boundary and outer boundary of the low-population
zone were analyzed, using the models described in Appendix 15A.
15.6.3.3.1.4 Identification of Leakage Pathways and Resultant Leakage Activity
The activity released from the faulted steam generator, is released directly to
the environment by the atmospheric relief valves. The intact steam generators
discharge steam and entrained activity via the safety and atmospheric relief
valves until the time that initiation of the RHR system can be accomplished.
In addition, the steam release via the exhaust stack of the TDAFW pumps is also
considered in the SGTR dose consequences shown in Table 15.6-4. Since the
activity is released directly to the environment with no credit for plateout or
fall out, the results of the analysis are based on the most direct leakage
pathway available. Therefore, the resulting radiological consequences
represent a conservative estimate of the potential integrated dose to the
postulated SGTR.
15.6.3.3.2 Identification of Uncertainties and Conservatisms in
the Analysis
- a. Reactor coolant activities based on extreme iodine spiking effects are conservatively high.
- b. The assumed 1-gpm steam generator primary-to-secondary leakage is greater than that anticipated during normal operation.
- c. Tube rupture of the steam generator is assumed to be a double-ended severance of a single steam generator tube. This is a conservative
assumption, since the steam generator tubes are constructed of
highly ductile materials. The more probable mode of tube failure
is one or more minor leaks of undetermined origin. Activity in the
secondary steam system is subject to continual surveillance, and
the accumulation of activity from minor leaks that exceeds the
limits established in the technical specifications would lead to
reactor shutdown. Therefore, it is unlikely that the total amount
of activity considered available for release in this analysis would
ever be realized.
15.6-16 Rev. 22 WOLF CREEK
- d. The coincident loss of offsite power with the occurrence of an SGTR is a conservative assumption. In the event of the
availability of offsite power, the condenser dump valves will open, permitting steam dump to the condenser. This will reduce the
amount of steam and entrained activity discharged directly to the
environment from the unaffected steam generators.
- e. The radiological consequences have been based on a worst-case scenario, i.e., forced steam generator overfill with a stuck-open
safety valve.
- f. The meteorological conditions which may be present at the site during the course of the accident are uncertain. However, it is
unlikely that meteorological conditions assumed will be present
during the course of the accident for any extended period of time.
Therefore, the radiological consequences evaluated, based on the
meteorological conditions assumed, are conservative.
15.6.3.3.3 Conclusions
15.6.3.3.3.1 Filter Loadings
The only ESF filtration system considered in the analysis which limits the
consequences of the steam generator tube rupture is the control room filtration
system. Activity loadings on the control room charcoal filter are based on
flow rate through the filter, concentration of activity at the filter inlet, and filter efficiency.
Activity in the control room filter as a function of time has been evaluated
for the LOCA, Section 15.6.5. Since the control room filters are capable of
accommodating the potential design-basis LOCA fission product iodine loadings, more than adequate design margin is available with respect to postulated SGTR
accident releases.
15.6.3.3.3.2 Doses to Receptor at the Exclusion Area Boundary
Consistent with the current methodology for evaluating radiological consequences of a postulated SGTR, along with the changes mentioned in Section 15.6.3.3.1, the offsite (Exclusion Area Boundary and Low Population Zone) doses to the thyroid and whole body have been calculated, using the RADTRAD 3.03 computer code (Reference 8). The results of the dose calculations are presented in Table 15.6-5. As can be seen from this table, the calculated radiological consequences of a postulated steam generator tube failure accident do not exceed: (1) the exposure guidelines as set forth in 10 CFR Part 100, Section 11 for the accident with an assumed pre-accident iodine spike, and (2) a small fraction (i.e., 10%) of these exposure guidelines, for the accident with an equilibrium iodine concentration in combination with an assumed accident initiated iodine spike.
15.6.3.4 Conclusions
A steam generator tube rupture will cause no subsequent damage to the RCS or
the reactor core. An orderly recovery from the accident can be completed, even
assuming simultaneously loss of offsite power.
15.6-17 Rev. 22 WOLF CREEK 15.6.
3.5 REFERENCES
- 1. Letter SLNRC 86-1, Petrick, N. A., SNUPPS to Denton, H. R.
(NRC), "Steam Generator Single-Tube Rupture Analysis for
SNUPPS Plants - Callaway and Wolf Creek", dated
January 8,1986.
- 2. Letter WM 87-0145, Withers, B. D. WCNOC to US NRC, "Response
to RAI Regarding the SGTR Overfill Case Analysis", dated
May 15, 1987.
- 3. McFadden, J. H., et al, "RETRAN A Program for Transient
Thermal Hydraulic Analysis of Complex Fluid Flow Systems",
EPRI-NP-1850-CCM-A, October 1984.
- 4. Letter from NRC to Withers, B. D., "Safety Evaluation Report for the Wolf Creek Generating Station Steam Generator Tube Rupture Analysis", TAC No.
57363, dated May 7, 1991.
- 5. Stewart, C. W., et. al., "VIPRE-01: A Thermal-Hydraulic Code for Reactor Cores," Battelle, Pacific Northwest Laboratories, EPRI NP-2511-CCM-A, August 1989.
- 6. Paulsen, M. P., et. al., "RETRAN-3D: A Program for Transient Thermal-Hydraulic Analysis of Complex Fluid Flow Systems," EPRI NP-7450(A). July 2001. 7. Regulatory Guide 1.195, "Methods and Assumptions for Evaluating Radiological Consequences of Design Basis Accidents at Light-Water Nuclear Power Reactors," May 2003.
- 8. NUREG/CR-6604, "RADTRAD: A Simplified Model for Radionuclide Transport and Removal and Dose Estimation," S. L. Humphreys et. al., November 1998.
15.6.4 SPECTRUM OF BWR STEAM SYSTEM PIPING FAILURES OUTSIDE OF
CONTAINMENT
This section is not applicable to WCGS.
15.6.5 LOSS-OF-COOLANT ACCIDENTS RESULTING FROM A SPECTRUM OF
POSTULATED PIPING BREAKS WITHIN THE REACTOR COOLANT
PRESSURE BOUNDARY
15.6.5.1 Identification of Causes and Frequency Classification
A loss-of-coolant accident (LOCA) is the result of a pipe rupture of the
reactor coolant system (RCS) pressure boundary. For the analysis reported
here, a small break is defined as a rupture of the RCS piping with a cross-
sectional area less than 1.0ft 2 , in which the normally operating charging system flow is not sufficient to sustain pressurizer level and pressure. A
small break LOCA is classified as an ANS Condition III event (an infrequent
fault), as defined in Section 15.0. A major break (large break) is defined as
a rupture with a total cross-sectional area equal to or greater than 1.0ft
- 2. This event is considered an ANS Condition IV event, a limiting fault, in that
it is not expected to occur during the life of a plant but is postulated as a
conservative design basis.
The Acceptance Criteria for the LOCA are described in 10 CFR 50.46 as follows:
A. The calculated peak fuel element clad temperature shall not exceed the requirement of 2200°F.
15.6-18 Rev. 22 WOLF CREEK B. The amount of fuel element cladding that reacts chemically with water or steam to generator hydrogen, shall not exceed 1 percent of the total
amount of Zircaloy in the fuel cladding.
C. The clad temperature transient is terminated at a time when the core geometry is still amenable to cooling. The localized cladding oxidation
limit of 17 percent is not exceeded during or after quenching.
D. The core remains amenable to cooling during and after the break.
E. The core temperature is reduced and decay heat is removed for an extended period of time, as required by the long-lived radioactivity
remaining in the core.
These criteria were established to provide a significant margin in emergency
core cooling system (ECCS) performance following a LOCA. WASH-1400 (USNRC
1975) Reference 2) presents a study in regards to the probability of occurrence
of RCS pipe ruptures.
In all cases, small breaks (Less than 1.0 ft.
- 2) yield results with more margin to the Acceptance Criteria Limits than large breaks.
Major plant systems and equipment available for mitigation of transient and
accident conditions are discussed in Section 15.0.8 and listed in Table 15.0-6.
The actual parameters assumed and results are given in the respective
section/subsection. Table 15.0-6 incorporates events shown in the sequence
diagram, Figure 15.0-25.
15.6.5.2 Sequence of Events and Systems Operations
Should a major pipe break occur, depressurization of the RCS results in a
pressure decrease in the pressurizer. The reactor trip signal subsequently
occurs when the pressurizer low pressure trip setpoint is reached. A safety
injection signal is generated when the appropriate setpoint (high containment
pressure or low pressurizer pressure) is reached. These countermeasures limit
the consequences of the accident in two ways:
A. Reactor trip and borated water injection supplement void formation in
causing rapid reduction of power to the residual level corresponding to fission
product decay heat. No credit is taken in the LOCA analysis for the boron
content of the injection water. However, an average RCS/sump mixed boron
concentration is calculated and verified on a cycle-specific basis to ensure
that the post-LOCA core remains subcritical. In addition, the insertion of
control rods to shut down the reactor is neglected in the large break analysis, but is credited in the post-LOCA subcriticality evaluation. Details on the
method for assuring post-LOCA subcriticality is discussed in Section
15.6.5.3.4.
B. Injection of borated water provides for heat transfer from the core and
prevents excessive clad temperatures.
15.6-19 Rev. 29 WOLF CREEK Description of the Large Break LOCA Transient Before the break occurs, the RCS (Reactor Coolant System) is assumed to be operating normally at full power in an equilibrium condition, i.e., the heat generated in the core is being removed via the secondary system. A large break is assumed to open instantaneously in one of the main RCS cold leg pipes. Immediately following the cold leg break, a rapid system depressurization occurs along with a core flow reversal due to a high discharge of sub-cooled fluid into the broken cold leg and out of the break. The fuel rods go through departure from nucleate boiling (DNB) and the cladding rapidly heats up, while the core power decreases due to voiding in the core. The hot water in the core, upper plenum, and upper head flashes to steam, and subsequently the cooler water in the lower plenum and downcomer begins to flash. Once the system has depressurized to the accumulator pressure, the accumulator begins to inject cold borated water into the intact cold legs. During the blowdown period, a portion of the injected Emergency Core Cooling System (ECCS) water is calculated to be bypassed around the downcomer and out of the break. The bypass period ends as the system pressure continues to decrease and approaches the containment pressure, resulting in reduced break flow and consequently, reduced core flow. As the refill period begins, the core continues to heat up as the vessel begins to fill with ECCS water. This phase continues until the lower plenum is filled, the bottom of the core begins to reflood, and entrainment begins. During the reflood period, the core flow is oscillatory as ECCS water periodically rewets and quenches the hot fuel cladding, which generates steam and causes system re-pressurization. The steam and entrained water must pass through the vessel upper plenum, the hot legs, the steam generators, and the reactor coolant pumps before it is vented out of the break. This flow path resistance is overcome by the downcomer water elevation head, which provides the gravity driven reflood force. The pumped cold leg injection ECCS water aids in the filling of the vessel and downcomer, which subsequently supplies water to maintain the core and downcomer water levels and complete the reflood period. The time sequence of events for the PCT limiting Large Break LOCA case is given in Table 15.6-10.
15.6-20 Rev. 29 WOLF CREEK Description of Small-Break LOCA Transient
As contrasted with the large break, the blowdown phase of the small break
occurs over a longer time period. Thus, for a small-break LOCA there are only
three characteristic stages, i.e., a gradual blowdown in which the decrease in
water level is checked, core recovery, and long-term recirculation.
15.6.5.3 Core and System Performance
15.6.5.3.1 Mathematical Model
The requirements of an acceptable ECCS evaluation model are presented in 10 CFR 50.46 and Appendix K of 10 CFR 50 (Reference 10). Large Break LOCA Evaluation Model General: When the Final Acceptance Criteria (FAC) governing the loss-of-coolant accident (LOCA) for Light Water Reactors was issued in 10 CFR 50.46 (Reference 10), both the Nuclear Regulatory Commission (NRC) and the industry recognized that stipulations of Appendix K were highly conservative. That is, using the then accepted analysis methods, the performance of the Emergency Core Cooling System (ECCS) would be conservatively underestimated, resulting in predicted peak cladding temperatures (PCT's) much higher than expected. At that time, however, the degree of conservatism in the analysis could not be quantified. As a result, the NRC began a large-scale confirmatory research program with the following objectives: 1. Identify, through separate effects and integral effects experiments, the degree of conservatism in those models required in the Appendix K rule. In this fashion, those areas in which a purposely prescriptive approach was used in the Appendix K rule could be quantified with additional data so that a less prescriptive future approach might be allowed. 2. Develop improved thermal-hydraulic computer codes and models so that more accurate and realistic accident analysis calculations could be performed. The purpose of this research was to develop an accurate predictive capability so that the uncertainties in the ECCS performance and the degree of conservatism with respect to the Appendix K limits could be quantified. Since that time, the NRC and the nuclear industry have sponsored reactor safety research programs directed at meeting the above two objectives. The overall results have quantified the conservatism in the Appendix K rule for LOCA analyses and confirmed that some relaxation of the rule can be made without a loss in safety to the public. It was also found that some plants were being restricted in operating flexibility by overly conservative Appendix K requirements. In recognition of the Appendix K conservatism that was being quantified by the research programs, the NRC adopted an interim approach for evaluation methods. This interim approach is described in SECY-83-472 (Reference 15). The SECY-83-472 approach retained those features of Appendix K that were legal requirements, but permitted applicants to use best-estimate thermal-hydraulic models in their ECCS evaluation model. Thus, SECY-83-472 represented an important step in basing licensing decisions on realistic calculations, as opposed to those calculations prescribed by Appendix K. 15.6-21 Rev. 29 WOLF CREEK In 1988, the NRC Staff amended the requirements of 10 CFR 50.46 and Appendix K, "ECCS Evaluation Models", to permit the use of a realistic evaluation model to analyze the performance of the ECCS during a hypothetical LOCA. This decision was based on an improved understanding of LOCA thermal-hydraulic phenomena gained by extensive research programs. Under the amended rules, best estimate thermal-hydraulic models may be used in place of models with Appendix K features. The rule change also requires, as part of the LOCA analysis, an assessment of the uncertainty of the best estimate calculations. It further requires that this analysis uncertainty be included when comparing the results of the calculations to the prescribed acceptance criteria of 10 CFR 50.46. Further guidance for the use of best estimate codes is provided in Regulatory Guide 1.157 (Reference 16). To demonstrate use of the revised ECCS rule, the NRC and its consultants developed a method called the Code Scaling, Applicability, and Uncertainty (CSAU) evaluation methodology (Reference 24). This method outlined an approach for defining and qualifying a best estimate thermal-hydraulic code and quantifying the uncertainties in a LOCA analysis (Figure 15.6-5). A LOCA evaluation methodology for three and four loop pressurized water reactor (PWR) plants based on the revised 10 CFR 50.46 rules was developed by Westinghouse with the support of EPRI and Consolidated Edison and has been approved by the NRC (Reference 6). More recently, Westinghouse developed an alternative uncertainty methodology called ASTRUM, which stands for Automated Statistical Treatment of Uncertainty Method (Reference 9). This method is still based on the CQD methodology and follows the steps in the CSAU methodology. However, the uncertainty analysis (Element 3 in the CSAU) is replaced by a technique based on order statistics. The ASTRUM methodology replaces the response surface technique with a statistical sampling method where the uncertainty parameters are simultaneously sampled for each case. The ASTRUM methodology has received NRC approval for referencing in licensing applications in WCAP-16009-P-A (Reference 9). The ASTRUM methodology requires the execution of 124 transients to determine a bounding estimate of the 95th percentile (with 95% confidence level) of the Peak Cladding Temperature (PCT), Local Maximum Oxidation (LMO), and Core Wide Oxidation (CWO) to satisfy the 10 CFR 50.46 criteria. This analysis is in accordance with the applicability limits and usage conditions defined in Section 13-3 of WCAP-16009-P-A (Reference 9) as applicable to the ASTRUM methodology. Section 13-3 of WCAP-16009-P-A (Reference 9) was found to acceptably disposition each of the identified conditions and limitations related to WCOBRA/TRAC and the CQD uncertainty approach per Section 4.0 of the ASTRUM Final Safety Evaluation Report (SER) appended to this Topical Report. The Best-Estimate LBLOCA analysis and associated model for Wolf Creek is plant-specific. The Wolf Creek ASTRUM LBLOCA uses a plant-specific adaptation of the ASTRUM methodology that includes explicit modeling of fuel thermal conductivity degradation (TCD), as well as a larger range for rod internal pressure (RIP) uncertainty. Additionally the ASTRUM LBLOCA analysis was performed using heat transfer multipliers different than those used in the as-approved ASTRUM methodology. These heat transfer multiplier distribution changes have been reported to the NRC in Reference 29. Development of WCOBRA/TRAC Computer Code: The COBRA/TRAC code was originally developed at Pacific Northwest Laboratory (Reference 1) by combining the COBRA-TF code (Reference 8) and the TRAC-PD2 codes (Reference 3). The COBRA-TF code, which has the capability to model three-dimensional flow behavior in a reactor vessel, was incorporated into 15.6-22 Rev. 29 WOLF CREEK TRAC-PD2 to replace its vessel model. TRAC-PD2 is a systems transient code designed to model all major components in the primary system. Westinghouse continued the development and validation of COBRA/TRAC through the FLECHT-SEASET program (Reference 4). To allow the code to model phenomena specific to plants with upper plenum injection, Westinghouse made modifications and improvements to COBRA/TRAC and renamed the new version WCOBRA/TRAC Mod 4 (Reference 5). Westinghouse continued the development of WCOBRA/TRAC to extend its application to three- and four-loop Westinghouse Pressurized Water Reactors (PWR's) with cold-leg injection with version MOD7A, Revision 1. This computer code is described in detail in a WCAP-12945-P-A, referred to as the Code Qualification Document (CQD) (Reference 6) as well as WCAP-16009-P-A, which describes the ASTRUM methodology (Reference 9). WCAP-16009-P-A (Reference 9) states that the ASTRUM methodology is based on the frozen version of WCOBRA/TRAC MOD7A, Revision 6. WCOBRA/TRAC MOD7A, Revision 8 was used for the execution of the ASTRUM Uncertainty Studies for Wolf Creek. The confirmatory analysis (paragraph "Determination of Plant Operating Conditions") was executed with WCOBRA/TRAC MOD7A Revision 7. The Nuclear Regulatory Commission (NRC) approved Westinghouse Best-Estimate Loss-of-Coolant Accident (BELOCA) ASTRUM methodology (Reference 9) based on the PAD 4.0 fuel performance code (Reference 28). PAD 4.0 was licensed without explicitly considering fuel thermal conductivity degradation (TCD) with burnup. Explicit modeling of TCD in the fuel performance code leads directly to increased fuel temperatures (pellet radial average temperature) as well as other fuel performance related effects beyond beginning-of-life. Since PAD provides input into the large-break LOCA analysis, this will tend to increase the stored energy at the beginning of the simulated large-break LOCA event. This in turn leads to an increase in Peak Cladding Temperature (PCT) if there is no provision to credit off-setting effects. In addition, a different fuel thermal conductivity model in WCOBRA/TRAC and HOTSPOT was used to more accurately model the fuel temperature profile when accounting for TCD. In order to mitigate the impact of the increasing effect of pellet TCD with burnup, the large-break LOCA evaluation of second/third cycle fuel utilizing reduced peaking factors from those shown in USAR Table 15.6-9. The reduced peaking factors are limited to the following application: burndown credit for the hot rod and hot assembly is taken for higher burnup fuel in the second/third cycle of operation. The Wolf Creek peaking factor values utilized in this analysis are shown in Table 15.6-9B. Note that the beginning to middle of life values are the Table 15.6-9 values. Evaluation of the fuel in its second/third cycle of irradiation is beyond the first cycle considered in the approved ASTRUM Evaluation Model (EM), but was considered in the analysis when explicitly modeling TCD to demonstrate that conformance to the acceptance criteria is met for the second/third cycle fuel. In addition to the standard uncertainty calculations, the Wolf Creek LBLOCA analysis sampled a larger rod internal pressure (RIP) uncertainty than originally included in the ASTRUM methodology (Reference 9). It was discovered that the as-approved sampling range did not bound the plant-specific rod internal pressure uncertainties for Wolf Creek. Therefore, the approved sampling range was expanded to bound the Wolf Creek plant-specific data. WCOBRA/TRAC combines two-fluid, three-field and multi-dimensional fluid equations used in the vessel with one-dimensional drift-flux equations used in the loops to allow a complete and detailed simulation of a PWR. This best-estimate computer code contains the following features:
- 1. Ability to model transient three-dimensional flows in different geometries inside the vessel
- 2. Ability to model thermal and mechanical non-equilibrium between phases
- 3. Ability to mechanistically represent interfacial heat, mass, and momentum transfer in different flow regimes 15.6-23 Rev. 29 WOLF CREEK
- 4. Ability to represent important reactor components such as fuel rods, steam generators, reactor coolant pumps, etc. The two-fluid formulation uses a separate set of conservation equations and constitutive relations for each phase. The effects of one phase on another are accounted for by interfacial friction and heat and mass transfer interaction terms in the equations. The conservation equations have the same form for each phase; only the constitutive relations and physical properties differ.
Dividing the liquid phase into two fields is a convenient and physically accurate way of handling flows where the liquid can appear in both film and droplet form. The droplet field permits more accurate modeling of thermal-hydraulic phenomena, such as entrainment, de-entrainment, fallback, liquid pooling, and flooding. WCOBRA/TRAC also features a two-phase, one-dimensional hydrodynamic formulation. In this model, the effect of phase slip is modeled indirectly via a constitutive relationship that provides the phase relative velocity as a function of fluid conditions. Separate mass and energy conservation equations exist for the two-phase mixture and for the vapor. The reactor vessel is modeled with the three-dimensional, three-field model, while the loops, major loop components, and safety injection points are modeled with the one-dimensional model. All geometries modeled using the three-dimensional model are represented as a matrix of cells. The number of mesh cells used depends on the degree of detail required to resolve the flow field, the phenomena being modeled, and practical restrictions such as computing costs and core storage limitations. The equations for the flow field in the three-dimensional model are solved using a staggered difference scheme on the Eulerian mesh. The velocities are obtained at mesh cell faces, and the state variables (e.g., pressure, density, enthalpy, and phasic volume fractions) are obtained at the cell center. This cell is the control volume for the scalar continuity and energy equations. The momentum equations are solved on a staggered mesh with the momentum cell centered on the scalar cell face. The basic building block for the mesh is the channel, a vertical stack of single mesh cells. Several channels can be connected together by gaps to model a region of the reactor vessel. Regions that occupy the same level form a section of the vessel. Vessel sections are connected axially to complete the vessel mesh by specifying channel connections between sections. Heat transfer surfaces and solid structures that interact significantly with the fluid can be modeled with rods and unheated conductors. One-dimensional components are connected to the vessel. The basic scheme used also employs the staggered mesh cell. The one-dimensional components consist of all the major components in the primary system, such as pipes, pumps, valves, steam generators, and the pressurizer. The one-dimensional components are represented by a two-phase, five-equation, drift flux model. This formulation consists of two equations for the conservation of mass, two equations for the conservation of energy, and a single equation for the conservation of momentum. Closure for the field equations requires specification of the interphase relative velocities, interfacial heat and mass transfer, and other thermodynamic and constitutive relationships. Methodology: WCAP-16009-P-A (Reference 9) provides ASTRUM methodology and also includes a description of the code models and their implementation. Volumes II and III of the CQD (Reference 6) presented a detailed assessment of the computer code WCOBRA/TRAC through comparisons to experimental data. From this assessment, a quantitative estimate was obtained of the code's ability to predict peak clad temperatures (PCT's) in a PWR large-break loss-of-coolant accident (LOCA). Modeling of a PWR introduced additional uncertainties, which were identified and discussed in Section 21 of the CQD Volume IV (Reference 6). A list of key 15.6-24 Rev. 29 WOLF CREEK LOCA parameters was compiled as a result of these studies. Models of several PWRs were used to perform sensitivity studies and establish the relative importance of these parameters. The final step of the best-estimate methodology, in which all the important uncertainties of the LOCA parameters are accounted for to estimate PCT, local maximum oxidation (LMO), and core-wide oxidation (CWO) at 95-percent probability. The methodology is summarized below: - Plant Model Development In this step, a WCOBRA/TRAC model of the plant is developed. A high level of noding detail is used to ensure an accurate simulation of the transient. Specific guidelines are followed to assure that the model is consistent with models used in the code validation. This results in a high level of consistency among plant models, with some plant-specific modeling dictated by hardware differences such as in the upper plenum of the reactor vessel or the Emergency Core Cooling System (ECCS) injection configuration. - Determination of Plant Operating Conditions In this step, the expected or desired operating range of the plant to which the analysis is to be applied is established using information supplied by the utility. The parameters considered are based on a "key LOCA parameters" list that was developed as part of the methodology. A set of these parameters, at mostly nominal values, is chosen as initial conditions to the plant model. A transient is run utilizing these parameters and is known as the "initial transient." Next, several confirmatory runs are made, which vary a subset of the key LOCA parameters over their expected operating range in one-at-a-time sensitivities. Because certain parameters are not included in the uncertainty analysis, these parameters are set at their bounding condition. This analysis is commonly referred as the confirmatory analysis. The typical four sets of parameters evaluated in the confirmatory analysis are: High average temperature (Tavg) versus Low Tavg, High Steam Generator Tube Plugging (SGTP) level versus Low SGTP, High relative power in the low power peripheral assemblies (PLOW) versus Low PLOW, and Loss of Offsite Power (LOOP) versus no-LOOP. The most limiting input conditions, based on these confirmatory runs, are then combined into the model that will represent the limiting state for the plant, which is the starting point for the assessment of uncertainty. The confirmatory configuration analysis was performed previous to the ASTRUM uncertainty analysis prior to the identification of the TCD issue and associated PAD data. However, since the effects of TCD, analysis input changes (i.e., safety injection flow), and code version change (i.e., WC/T MOD7A, Revision 7 to WC/T MOD7A, Revision 8) were judged to have a negligible impact on the confirmatory study results, the limiting plant configuration (referred to as the Reference Transient) was judged to remain the same. - Assessment of Uncertainty The ASTRUM methodology is based on order statistics. The technical basis of the order statistics is described in Section 11 of WCAP-16009-P-A (Reference 9). The determination of the PCT uncertainty, LMO uncertainty, and CWO uncertainty relies on a statistical sampling technique. According to the statistical theory, 124 WCOBRA/TRAC calculations are necessary to assess against the three 10 CFR 50.46 criteria (PCT, LMO, and CWO). The uncertainty contributors are sampled randomly from their respective distribution for each of the WCOBRA/TRAC calculations. The list of uncertainty parameters, which are randomly sampled for each WCOBRA/TRAC calculation, includes initial conditions, power distributions, and model uncertainties. The time in the cycle, break type (split or double-ended guillotine), and break size for the split break are also sampled as uncertainty contributors within the ASTRUM methodology. 15.6-25 Rev. 29 WOLF CREEK Results from the 124 calculations are tallied by ranking the PCT from highest to lowest. A similar procedure is repeated for LMO and CWO. The highest rank of PCT, LMO, and CWO will bound 95 percent of their respective populations with 95-percent confidence level. - Plant Operating Range The plant operating range over which the uncertainty evaluation applies is defined. Depending on the results obtained in the above uncertainty evaluation, this range may be the desired range established in step 2, or may be narrower for some parameters to gain additional margin. Small Break LOCA Evaluation Model The NOTRUMP and LOCTA-IV computer codes are used in the analysis of LOCA due to
small breaks in the RCS. The NOTRUMP computer code is a one-dimensional
general network code consisting of a number of advanced features. Among these
features are the calculation of thermal nonequilibrium in all fluid volumes, flow regime-dependent drift flux calculations with counter-current flow
limitations, mixture level tracking logic in multiple-stacked fluid nodes, and
regime-dependent heat transfer correlations. Also, safety injection into the
broken loop is modeled using the COSI condensation model (Reference 13). The
NOTRUMP small break LOCA emergency core cooling system (ECCS) evaluation model
was developed to determine the RCS response to design basis small break LOCAs
and to address the NRC concerns expressed in NUREG-0611, "Generic Evaluation of
Feedwater Transients and Small Break Loss-of-Coolant Accidents in Westinghouse
Designed Operating Plant." In NOTRUMP, the RCS is nodalized into volumes
interconnected by flowpaths. the broken loop is modeled explicitly with the
intact loops lumped into a second loop. The transient behavior of the system
is determined from the governing conservation equations of mass, energy, and
momentum applied throughout the system. A detailed description of NOTRUMP is
given in Reference 11, 12 and 13.
The use of NOTRUMP in the analysis involves, among other things, the
representation of the reactor core as heated control volumes with an associated
bubble rise model to permit a transient mixture height calculation. The
multinode capability of the program enables an explicit and detailed spatial
representation of various system components. In particular, it enables a
proper calculation of the behavior of the loop seal during a loss-of-coolant
transient.
Cladding thermal analyses are performed with the LOCTA-IV (Reference 7) code
which uses the RCS pressure, fuel rod power history, steam flow past the
uncovered part of the core, and mixture height history from the NOTRUMP
hydraulic calculations as input.
Figure 15.6-47 presents the hot rod axial power shape utilized to perform the
small-break analysis. This power shape represents a distribution of power
versus core height and was chosen because it maximizes the integral power at
the top half of the core where peak cladding temperature (PCT) occurs and
minimizes the power in the bottom half of the core, which reduces liquid swell
due to void formation thus providing a deeper core uncovery. This power shape
is skewed to the top of the core with the peak local power occurring at about
the 10-foot core elevation.
This is limiting for the small-break analysis, because of the core uncovery
process for small breaks. As the core uncovers, the cladding in the upper
elevation of the core heats up and is sensitive to the local power at that
elevation. The cladding temperatures in the lower elevation of the core, below
the two-phase mixture height, remain low. The peak clad temperature occurs
above 10 feet.
Schematic representation of the computer code interface is given in Figure
15.6-6.
15.6-26 Rev. 29 WOLF CREEK The small-break analysis was performed with the approved Westinghouse ECCS Small Break Evaluation Model with NOTRUMP (References 7, 11, 12, and 13).
15.6.5.3.2 Input Parameters and Initial Conditions
Large Break Analysis Input Parameters: The expected PCT and its uncertainty developed are valid for a range of plant operating conditions. The range of variation of the operating parameters has been accounted for in the uncertainty evaluation. Table 15.6-9 summarizes the operating ranges for Wolf Creek as defined for the proposed operating conditions, which are supported by the Best-Estimate LBLOCA analysis. Table 6.2.1-65 summarizes the LBLOCA containment data used for calculating containment pressure. If operation is maintained within these ranges, the LBLOCA results developed in this report are considered to be valid. Note that some of these parameters vary over their range during normal operation within a fuel cycle (e.g., accumulator temperature) and other parameters are typically fixed during normal operation within a fuel cycle (full-power Tavg). Small Break Specific Input Parameters and Initial Conditions
Significant input parameters are given in Table 15.6-9A.
For the small break LOCA (SBLOCA) analysis, loss of offsite power (LOOP) is
assumed, which results in the limiting single failure assumption of the loss of
one Emergency Diesel Generator (EDG) and a subsequent loss of one train of
pumped Emergency Core Cooling System (ECCS). The SBLOCA analysis assumes that
reactor trip occurs coincident with the LOOP, which results in the following: (a) Reactor Coolant Pump (RCP) trip and coastdown and (b) Steam Dump System
being inoperable.
The SBLOCA analysis is performed with a high nominal vessel average temperature (Tavg) value of 588.4 F and minimum auxiliary feedwater (AFW) flow rate of 210 gpm/SG. The high Tavg value chosen is evaluated to be applicable over the
range of nominal vessel average temperature values (570.7 F to 588.4 F) and the minimum AFW flow rate is evaluated to be applicable over a range of AFW flow rates (210-250 gpm/SG).
The safety injection (SI) system consists of gas pressurized accumulator tanks
and pumped injection systems. The accumulators are modeled to inject borated
water into the RCS when the RCS depressurizes to 583 psia. Minimum ECCS
availability is assumed for the analysis from one centrifugal charging pump (CCP), one SI pump and one RHR pump. Assumed pumped SI characteristics as a
function of RCS pressure used as boundary conditions in the analysis are shown
in Table 15.6-14 and corresponding Figure 15.6-46 for break sizes less than
8.75 inches and Table 15.6-14A and corresponding Figure 15.6-46A for the 8.75
inch break case. For the break sizes less than 8.75 inches the broken loop
safety injection flow is assumed to spill to RCS pressure and for the 8.75 inch
break case the broken loop safety injection flow is assumed to spill to the
containment back pressure of 0 psig. The ECCS was assumed to be delivering to
the RCS 39 seconds after the generation of the SI signal. This delay includes
time required for sensor response, diesel generator startup and emergency power
bus loading in case of a loss of offsite power coincident with an accident.
15.6.5.3.3 Results
Large Break LOCA Results The Wolf Creek PCT/LMO/CWO-limiting transients are double-ended cold leg guillotine break which analyzes conditions that fall within those listed in Table 15.6-9. Traditionally, cold leg breaks have been limiting for large break LOCA. This location is the one where flow stagnation in the core appears most likely to occur. Scoping studies with WCOBRA/TRAC have confirmed that the cold leg remains the limiting break location (WCAP-12945-P-A) (Reference 6). 15.6-27 Rev. 29 WOLF CREEK Engineering Inspection: The Large Break LOCA transient can be conveniently divided into a number of time periods in which specific phenomena are occurring. For a typical large break, the blowdown period can be divided into the critical heat flux (CHF) phase, the upward core flow phase, and the downward core flow phase. These are followed by the refill, reflood and long term cooling phases. The important phenomena occurring during each of these phases are discussed as follows. Plot results for the PCT limiting Transient are shown in Figures 15.6-7 through 15.6-21.
- 1. Critical Heat Flux (CHF) Phase:
Immediately following the cold leg rupture, the fluid discharged at the break is subcooled and high break flow rates are observed. During this early period the core flow reverses, the fuel rods go through Departure from Nucleate Boiling (DNB) and the cladding rapidly heats up while voiding in the core rapidly causes the fission power to drop. Figure 15.6-7 shows the HOTSPOT maximum cladding temperature and WC/T PCT in the core as a function of time, while Figure 15.6-8 provides the location of the peak cladding temperatures for the hot rod versus time. The regions of the RCS with the highest initial temperatures (core, upper plenum, and hot legs) begin to flash to steam during this period. This phase is terminated when the water in the lower plenum and downcomer begins to flash (Figures 15.6-13 and 15.6-17, respectively).
- 2. Upward Core Flow Phase:
Heat transfer is improved as the lower plenum fluid is pulled into the core. This effect may be enhanced if the pumps are not degraded (thus for cases with offsite power available), or the break discharge rate is reduced because the fluid is saturated at the break. Figure 15.6-9 shows the break flow rates for the vessel side and pump side. If pumps are highly degraded (as is the case for this PCT/CWO limiting Transient since a Loss-of-Offsite power (LOOP) is modeled at beginning of transient), or the break flow is large, the cooling effect due to upward flow may not be significant. The intact loop remains in single-phase liquid flow for a few seconds (Figure 15.6-10), resulting in enhanced upward core flow cooling. This phase ends as the lower plenum mass is depleted, the loop flow becomes two-phase and the pump head degrades.
- 3. Downward Core Flow Phase:
Downward flow in the core increases as the pump head continues to degrade (due to increased voiding and pump coastdown). The break flow then begins to dominate and pull flow down through the core, up the downcomer to the broken cold leg, and out the break. Figure 15.6-11 shows the vapor flow near the top of the core of the Hot Assembly Channel. While liquid and entrained liquid flows provide core cooling, the vapor flow near the top core best illustrates this phase of core cooling. This period may be enhanced by flow from the upper head. Once the system has depressurized to the accumulator pressure, the accumulators begin to inject cold borated water into the intact cold legs (Figure 15.6-14). During this period, due to steam upflow in the downcomer, a portion of the injected ECCS water is calculated to be bypassed around the downcomer and out the break. As the system pressure continues to fall, the break flow and the downward core flow are reduced. The system pressure (Figure 15.6-12) reaches the containment pressure (Figure 15.6-21) at the end of this last period of the blowdown phase, around 21 seconds. During this phase, the core begins to heat up as the system reaches containment pressure and the vessel begins to fill with Emergency Core Cooling System (ECCS) water.
- 4. Refill Phase:
Following the blowdown phase, the core experiences a nearly adiabatic heat-up as the lower plenum fills with ECCS water (Figure 15.6-13). This period is characterized by a rapid increase in cladding temperatures at all elevations due to the lack of liquid and steam flow in the core region. This phase ends when the ECCS water fills the lower plenum (Figure 15.6-13) and enters the 15.6-28 Rev. 29 WOLF CREEK core. At this time, a quench front is established and advances along the core and entrainment begins, with a resulting improvement in heat transfer. Figures 15.6-14, 15.6-15 and 15.6-16 show the liquid flows from the accumulator and the safety injection for an intact loop.
- 5. Reflood Phase:
During the early reflood phase, the accumulators begin to empty and nitrogen enters the system (Figure 15.6-14). The nitrogen surge forces water into the core, which then boils, causing system re-pressurization and the lower core region begins to quench. The repressurization is illustrated by the increase in downcomer liquid level (Figure 15.6-17). During this time, core cooling may increase due to vapor generation and liquid entrainment. During the reflood period, the core flow is oscillatory as cold water periodically rewets and quenches the hot fuel cladding, which generates steam and causes system re-pressurization. The steam and entrained water must pass through the vessel upper plenum, the hot legs, the steam generators and the reactor coolant pumps before it is vented out of the break. This flow path resistance is overcome by the downcomer water elevation head, which provides the gravity driven reflood force. From the later stage of blowdown to the beginning of reflood, the accumulators rapidly discharge borated cooling water into the RCS, filling the lower plenum and contributing to the filling of the downcomer. The pumped ECCS water aids in the filling of the downcomer and continue throughout the reflood period. Figures 15.6-17 and 15.6-18 show the downcomer and core liquid levels, respectively. Figure 15.6-19 shows the vessel fluid mass. As the quench front progresses further into the core, the PCT location moves higher towards the top core region. Figure 15.6-8 shows the movement of the PCT location. At approximately 90 seconds, after the accumulator injection is terminated, the stored energy in the vessel structures causes the downcomer and lower plenum water to start boiling, as illustrated, for example, by the lower plenum collapsed liquid level in Figure 15.6-13. The boiling of the downcomer and liquid plenum water causes a reduction in the downcomer, core levels, and vessel mass as the two-phase mixture level swell pushes water out of the break (see Figure 15.6-9). The downcomer boiling phenomenon is heavily affected by the containment pressure (which influences the steam density and the saturation temperature of the downcomer and lower plenum). The effect of downcomer boiling can be noticed on the PCT transient, although the general trend of decreasing cladding temperature is maintained, and the cladding temperatures remain lower than the limiting values observed earlier during the reflood period. As the transient progresses, continued injection of ECCS water refills the downcomer and core, removes the vessel metal mass stored energy, and leads to an increase in the vessel fluid mass. The quench time is approximately 310 seconds (Figure 15.6-7). Post Analysis of Record Evaluation: An evaluation of IFBA fuel including the effects of pellet TCD was performed, and shows that non-IFBA fuel bounds IFBA fuel. In addition to the analyses presented in this section, evaluations and reanalyses may be performed in the future as needed to address computer code errors and emergent issues, or to support plant changes. The issues or changes are evaluated, and the impact on the Peak Cladding Temperature (PCT) is determined. The resultant increase or decrease in PCT is applied to the analysis of record PCT for the large break LOCA. The current PCT presented in Table 15.6-11 is demonstrated to be less than the 10 CFR 50.46(b) requirement of 2200 o F. In addition, 10 CFR 50.46 requires that licensees assess and report the effect of changes to or errors in the evaluation model used in the large break LOCA analysis. These reports constitute addenda to the analysis of record provided in the USAR until the overall changes become significant as defined by 10 CFR 50.46. If the assessed changes or errors in the evaluation model results in significant changes in calculated PCT, a schedule for formal reanalysis or other action as needed to show compliance will be addressed in the report to the NRC. 15.6-29 Rev. 29 WOLF CREEK Finally, the criteria of 10 CFR 50.46 require that holders and users of the evaluation models establish a number of definitions and processes for assessing changes in the models or their use. Westinghouse, in consultation with the PWR Owner's Group (PWROG), has developed an approach for compliance with the reporting requirements. This approach is documented in WCAP-13451 (Reference 27), Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting. Wolf Creek Nuclear Operating Corporation provides the NRC with annual and 30-day reports, as applicable. Wolf Creek Nuclear Operating Corporation intends to provide future reports required by 10 CFR 50.46 consistent with the approach described in WCAP-13451.
Conclusions:
It must be demonstrated that there is a high level of probability that the limits set forth in 10 CFR 50.46 are met. The demonstration that these limits are met is as follows: (b)(1) The limiting PCT corresponds to a bounding estimate of the 95 th percentile PCT at the 95-percent confidence level. Since the resulting PCT for the limiting case is 1900 o F, the analysis confirms that 10 CFR 50.46 acceptance criterion (b)(1), i.e., "Peak Cladding Temperature less than 2200 o F", is demonstrated. The results are shown in Table 15.6-11. (b)(2) The maximum cladding oxidation corresponds to a bounding estimate of the 95 th percentile LMO at the 95-percent confidence level. Since the resulting LMO for the limiting case is 4.21 percent, the analysis confirms that 10 CFR 50.46 acceptance criterion (b)(2), i.e., "Local Maximum Oxidation of the cladding less than 17 percent of the total cladding thickness before oxidation", is demonstrated. The results are shown in Table 15.6-11. (b)(3) The limiting core-wide oxidation corresponds to a bounding estimate of the 95 th percentile CWO at the 95-percent confidence level. The limiting Hot Assembly Rod (HAR) total maximum oxidation is 0.1352 percent. A detailed CWO calculation takes advantage of the core power census that includes many lower power assemblies. Because there is significant margin to the regulatory limit, the CWO value can be conservatively chosen as that calculated for the limiting HAR. A detailed CWO calculation is therefore not needed because the outcome will always be less than the HAR value. Since the resulting CWO is 0.1352 percent, the analysis confirms that 10 CFR 50.46 acceptance criterion (b)(3), i.e., "Core-Wide Oxidation less than 1 percent", is demonstrated. The results are shown in Table 15.6-11. (b)(4) 10 CFR 50.46 acceptance criterion (b)(4) requires that the calculated changes in core geometry are such that the core remains amenable to cooling. This criterion has historically been satisfied by adherence to criteria (b)(1) and (b)(2), and by assuring that fuel deformation due to combined LOCA and seismic loads is specifically addressed. Criteria (b)(1) and (b)(2) remain in effect for BE LOCA applications. The approved methodology (WCAP-12945-P-A) (Reference 6) specifies that effects of LOCA and seismic loads on core geometry do not need to be considered unless grid crushing extends beyond the 44 assemblies in the low-power channel. This situation remains unchanged with the application of the ASTRUM methodology (Reference 9). (b)(5) 10 CFR 50.46 acceptance criterion (b)(5) requires that long-term core cooling be provided following the successful initial operation of the ECCS. Long-term cooling is dependent on the demonstration of continued delivery of cooling water to the core. The manual or automatic actions that are currently in place to maintain long-term cooling remain unchanged with the application of the ASTRUM methodology (Reference 9). Based on the ASTRUM Analysis results (Table 15.6-11), it is concluded that Wolf Creek continues to maintain a margin of safety to the limits prescribed by 10 CFR 50.46. 15.6-30 Rev. 29 WOLF CREEK The maximum calculated peak clad temperature for all small breaks analyzed is 936°F. The results of the analyses given in Table 15.6-12 are well below all Acceptance Criteria limits of 10 CFR 50.46, and in all cases are not limiting
when compared to the results presented for large breaks.
15.6.5.3.4 Post-LOCA Long-Term Core Cooling/Subcriticality
10CFR50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light
Water Nuclear Power Reactors" paragraph (b) item (5) sets forth the
requirements for post-LOCA long-term core cooling. To satisfy the
requirements, the core is maintained in a shutdown state solely by the soluble
boron contained in the ECCS water after a LOCA because credit for the shutdown provided by the control rods was not taken for cold leg breaks 3.0 ft 2 , or hot leg breaks 1.0 ft 2. Since safety injection flow is drawn from the sump following switchover from the RWST, the containment sump post-LOCA boron concentration must be higher than the boron concentration required to ensure
subcritical conditions.
To determine if the requirements for post-LOCA long-term core cooling
subcriticality are met, a calculation is performed for each reload to determine
the boron concentration required to keep the core subcritical (K eff < 1.0) and the mixed mean boron concentration (MMBC) of the post-LOCA sump water. This
calculation, documented in the cycle-specific Reload Safety Analysis Checklist (RSAC), confirms that the post-LOCA sump MMBC exceeds the core critical boron
concentration, thereby ensuring the reload core remains subcritical. Note:
The post-LOCA long-term core cooling critical boron concentration is determined
at the most reactive time in life, assuming an all rods out (ARO) no Xenon condition and a post-LOCA fluid temperature range of 68-212 F. All sources of water that may eventually reside in the containment sump at cold leg recirculation switchover time and their respective pre-accident boron
concentrations are considered.
Westinghouse has identified a potential safety issue concerning core
recriticality following a large break cold leg break LOCA (Reference 19). The
potential safety issue is that during hot leg switchover the core will be
flushed with a diluted sump solution, which may cause the core to return to
criticality. The sump solution would become diluted as boron accumulates in
the core during the core leg recirculation phase due to core boiling. The
accumulation of boron in the core prevents the boron from being displaced to
the sump which leads to a diluted sump solution.
However, a generic assessment (Reference 19) concludes that for any given plant
and fuel cycle, the boron worth of the inserted control rods plus the
equivalent boron worth due to the presence of Xenon at the time of hot leg
switchover, would offset any reasonable calculation of sump dilution. As
documented in WCAP-15704 (Reference 20), it was demonstrated that control rods
will insert following a licensing basis cold leg LOCA for 3-loop and 4-loop
Westinghouse plant designs. Thus, the negative reactivity credit associated
with control rods can be applied when evaluating recriticality at the time of
switchover to hot leg ECCS recirculation.
Consequently, post-LOCA subcriticality will continue to be confirmed using sump
boron calculations that do not consider sump dilution, but also use the
conservative assumptions of ARO and no Xenon at the most reactive time in life, with an assumed post-LOCA core/fluid temperature in the range of 68-212 F.
15.6-31 Rev. 29 WOLF CREEK 15.6.5.4 Radiological Consequences
15.6.5.4.1 Method of Analysis
The analysis of the radiological consequences of a postulated LOCA uses the
recommended dose conversion factors (DCFs) as follows:
(1) The analysis uses thyroid dose conversion factors (DCFs) for inhalation
of radionuclides based on the data provided in Table 2.1 of Federal
Guidance Report 11, "Limiting Values of Radionuclide Intake and Air
Concentration and Dose Conversion Factors for Inhalation, Submersion, and Ingestion". This is a departure from the more conservative DCF
values listed in Regulatory Guide 1.109, which were used in the previous
analysis of record, (2) The effective dose conversion factors, provided in Table III.1 of
Federal Guidance Report 12, "External Exposure to Radionuclides in Air, Water, and Soil", are used to calculate the whole body doses.
This deviates from the previous analysis of record, which used the more
conservative DCF values listed in Regulatory Guide 1.109, and using these DCFs
results in lower dose then would be obtained using the DCFs previously
presented in the LOCA analysis of record.
15.6.5.4.1.1 Containment Leakage Contribution
PHYSICAL MODEL - Following a postulated double-ended rupture of a reactor
coolant pipe with subsequent blowdown, the ECCS limits the clad temperature to
well below the melting point and ensures that the reactor core remains intact
and in a coolable geometry, minimizing the release of fission products to the
containment. However, to demonstrate that the operation of a nuclear power
plant does not represent any undue radiological hazard to the general public, a
hypothetical accident involving a significant release of fission products to
the containment is evaluated.
It is assumed that 100 percent of the noble gases and 50 percent of the iodine
equilibrium core saturation fission product inventory is immediately released
to the containment atmosphere. Of the iodine released to the containment, 50
percent is assumed to plateout onto the internal surfaces of the containment or
adhere to internal components. The remaining iodine and the noble gas activity
are assumed to be immediately available for leakage from the containment.
Once the gaseous fission product activity is released to the containment
atmosphere, it is subject to various mechanisms of removal which operate
simultaneously to reduce the amount of activity in the containment. The
removal mechanisms include radioactive decay, containment sprays, and
containment leakage. For the noble gas fission products, the only removal
processes considered in the containment are radioactive decay and containment
leakage.
- a. Radioactive Decay - Credit for radioactive decay for
fission product concentrations located within the
containment is assumed throughout the course of the
accident. Once the activity is released to the
environment, no credit for radioactive decay or
deposition is taken.
- b. Containment Sprays - The containment spray system is
designed to absorb airborne iodine fission products
within the containment atmosphere. To enhance the
iodine-removal capability of the containment sprays, sodium hydroxide is added to the spray solution. The
spray effectiveness for the removal of iodine is
dependent on the iodine chemical form.
15.6-32 Rev. 29 WOLF CREEK
- c. Containment Leakage - The containment leaks at a rate of
0.2 volume
percent/day as incorporated as a Technical
Specification requirement at peak calculated internal
containment pressure for the first 24 hours and at 50
percent of this leak rate for the remaining duration of
the accident. The containment leakage is assumed to be
directly to the environment.
ASSUMPTIONS AND CONDITIONS - The major assumptions and parameters assumed in
the analysis are itemized in Tables 15A-1 and 15.6-6.
In the evaluation of a LOCA, all the fission product release assumptions of
Regulatory Guide 1.4 have been followed. The following specific assumptions
were used in the analysis. Table 15.6-7 provides a comparison of the analysis
to the requirements of Regulatory Guide 1.4.
- a. The reactor core equilibrium noble gas and iodine
inventories are based on long-term operation at the
ultimate core power level of 3,565 MWt.
- b. One hundred percent of the core equilibrium radioactive
noble gas inventory is immediately available for leakage
from the containment.
- c. Twenty-five percent of the core equilibrium radioactive
iodine inventory is immediately available for leakage
from the containment.
- d. Of the iodine fission product inventory released to the
containment, 91 percent is in the form of elemental
iodine, 5 percent is in the form of particulate iodine, and 4 percent is in the form of organic iodine.
- e. Credit for iodine removal by the containment spray system
is taken, starting at time zero and continuing until a
decontamination factor of 100 for the elemental and
particulate species has been achieved.
- f. The following iodine removal constants for the con-
tainment spray system are assumed in the analysis:
Elemental iodine 10.0 hr -1 Organic iodine 0.0 hr -1 Particulate iodine 0.45 hr -1
- g. The following parameters were used in the two-region
spray model:
Fraction of containment sprayed - 0.85
Fraction of containment unsprayed - 0.15
Mixing rate (cfm) between sprayed and unsprayed
regions - 85,000
15.6-33 Rev. 29 WOLF CREEK Section 6.5 contains a detailed analysis of the sprayed
and unsprayed volumes and includes an explanation of the
mixing rate between the sprayed and unsprayed regions.
- h. The containment is assumed to leak at 0.2 volume
percent/day during the first 24 hours immediately
following the accident and 0.1 volume percent/day
thereafter.
- i. The containment leakage is assumed to be direct
unfiltered to the environment.
- j. The ESF filters are 90 percent efficient in the removal
of all species of iodine.
MATHEMATICAL MODELS USED IN THE ANALYSIS - Mathematical models used in the
analysis are described in the following sections:
- a. The mathematical models used to analyze the activity
released during the course of the accident are described
in Section 15A.2.
- b. The atmospheric dispersion factors used in the analysis
were calculated, based on the onsite meteorological
measurements program described in Section 2.3 and are
provided in Table 15A-2.
- c. The thyroid inhalation total-body immersion doses to a
receptor exposed at the exclusion area boundary and the
outer boundary of the low population zone were analyzed, using the models described in Sections 15A.2.4 and
15A.2.5, respectively.
- d. Buildup of activity in the control room and the
integrated doses to the control room personnel are
analyzed, based on models described in Section 15A.3.
IDENTIFICATION OF LEAKAGE PATHWAYS AND RESULTANT LEAKAGE ACTIVITY - For
evaluating the radiological consequences of a postulated LOCA, the resultant
activity released to the containment atmosphere is assumed to leak directly to
the environment.
No credit is taken for ground deposition or radioactive decay during transit to
the exclusion area boundary or LPZ outer boundary.
15.6.5.4.1.2 Radioactive Releases Due to Leakage from ECCS and
Containment Spray Recirculation Lines
15.6-34 Rev. 29 WOLF CREEK Subsequent to the injection phase of ESF system operation, the water in the
containment recirculation sumps is recirculated by the residual heat removal, centrifugal charging and safety injection pumps, and the containment spray
pumps. Due to the operation of the ECCS and the containment spray system, most
of the radioiodine released from the core would be contained in the containment
sump. It is conservatively assumed that a leakage rate of 2 gpm from the ECCS
and containment spray recirculation lines exists for the duration of the LOCA.
This leakage would occur inside the containment as well as inside the auxiliary
building. For this analysis, all the leakage is assumed to occur inside the
auxiliary building. Only trace quantities of radioiodine are expected to be
airborne within the auxiliary building due to the temperature and pH level of
the recirculated water. However, 10 percent of the radioiodine in the leaked
water is assumed to become airborne. This airborne iodine is assumed to be
released immediately to the environment from the unit vent, via the safety
grade filters associated with the auxiliary building emergency exhaust system.
No credit is taken for holdup or mixing in the auxiliary building; however, mixing and holdup in the containment sumps are included in the determination of
radioactive material releases and radioiodine removal through radioactive decay
for this leakage pathway.
Radiological Consequences of ECCS/CS Recirculation Line Leakage - The
assumptions used to calculate the amount of radioiodine released to the
environment are given in Table 15.6-6. The dose models are presented in
Section 15.A. The offsite doses at the site boundary and LPZ and the doses to
control room personnel from this pathway are given in Table 15.6-8.
15.6.5.4.1.3 Radioactive Releases Due to Operation of Containment Mini-Purge System
The containment mini-purge is designed to reduce the containment noble gas
concentration. The containment mini-purge system will be operated during power
operation if access to the containment is desired. The containment mini-purge
isolation valves are automatically closed upon a containment purge isolation
signal should a LOCA occur during containment purging when the reactor is at
power. The radioactive release via containment mini-purge will exist until the
containment isolation signal is received and the valves can be closed. Exhaust
from the containment is processed through the containment purge exhaust system
filter absorber train prior to discharge through the unit vent.
The maximum time for the purge valve closure is limited to five seconds to
assure that the purge valves would be closed before the onset of fuel failures
following a LOCA. Therefore, the source terms used in the radiological
consequences calculation is based on the fission product activity in the
primary coolant with consideration of pre-existing iodine spike. The
containment mini-pure system is assumed to be isolated within 5 seconds
following the initiation of the accident. The release rate from the
containment mini-purge system is assumed at 4680 cfm. Filter efficiency of 90%
for the removal of all species of iodine is assumed. Credit for iodine removal
by the containment spray system is not assumed in the analysis for activity
release via containment mini-purge system.
From the safety analysis perspective, it is acceptable to use either the
shutdown purge or mini-purge during refueling operations. This conclusion is
based on an assumption used in the fuel handling accident (FHA) involving the
radioactive material relief rate. To comply with Reg. Guide 1.25, all of the
gap activity in the damaged rods is assumed as a result of a FHA, to be
released and escape to the environment over a two-hour time period. The
analysis does not assume pathway, only that all the radioactivity is released
15.6-35 Rev. 29 WOLF CREEK from containment within a two hour period in some fashion. Thus the operation of a particular purge system, mini or shutdown is not of importance in the
analysis. This assumption translates into a very large air exhaust rate.
Therefore, the difference between the large volume containment shutdown purge
(20,000 cfm) and mini-purge (4,000 cfm) would have no impact on the calculated
dose consequences.
15.6.5.4.1.4 Radioactive Releases Due to Leakage from the Containment Sump to the RWST
The leakage pathway is from the containment recirculation sump through ECCS
boundary valves back to the RWST, which is vented to the atmosphere. It is
assumed that the activity released to the holdup system (in this case, the
containment recirculation sump) instantaneously diffuses to uniformly occupy
the sump volume. Removal mechanisms from the sump include decay and release (i.e., leakage) to the RWST.
It is assumed that 10% of the radioiodine leaked to the RWST becomes airborne, mixes with the RWST air volume, and is released to the environment. Credit is taken for radioactive decay in the RWST. The leakage rate from containment
sump to the RWST is assumed at 3.8 gpm for the duration of the accident. The RWST air volume is assumed to be 400,000 gallons. Other assumptions used to calculate the amount of radioiodine released to the environment are the same as
in the calculation for ECCS recirculation leakage inside the auxiliary
building.
15.6.5.4.2 Identification of Uncertainties and Conservatisms in
the Analysis
The uncertainties and conservatisms in the assumptions used to evaluate the
radiological consequences of a LOCA result principally from assumptions made
involving the amount of the gaseous fission products available for release to
the environment and the meteorology present at the site during the course of
the accident. The most significant of these assumptions are:
- a. The ECCS is designed to prevent fuel cladding damage that
would allow the release of the fission products contained
in the fuel to the reactor coolant. Severe degradation
of the ECCS (i.e., to the unlikely extent of simultaneous
failure of redundant components) would be necessary in
order for the release of fission products to occur of the
magnitude assumed in the analysis.
- b. The release of fission products to the containment is
assumed to occur instantaneously.
- c. It is assumed that 50 percent of the iodines released to
the containment atmosphere is plated-out onto the
internal surfaces of the containment or adheres to
15.6-36 Rev. 29 WOLF CREEK internal components; however, it is estimated that the removal of airborne iodines by various physical phenomena
such as adsorption, adherence, and settling could reduce
the resultant doses by a factor of 3 to 10 (Ref. 24).
- d. The activity released to the containment atmosphere is
assumed to leak to the environment at the containment
leakage rate of 0.2-volume percent/day for the first 24
hours and 0.1-volume percent/day thereafter. The initial
containment leakage rate is based on the peak calculated
internal containment pressure anticipated after a LOCA.
The pressure within the containment actually decreases
with time. Taking into account that the containment leak
rate is a function of pressure, the resultant doses could
be reduced by a factor of 5 to 10 (Ref. 24).
- e. The meteorological conditions assumed to be present at
the site during the course of the accident are based on
X/Q values, which are expected to be exceeded 5 percent
of the time. This condition results in the poorest
values of atmospheric dispersion calculated for the
exclusion area boundary and the LPZ outer boundary.
Furthermore, no credit has been taken for the transit
time required for activity to travel from the point of
release to the exclusion area boundary and LPZ outer
boundary. Hence, the radiological consequences evaluated
under these conditions are conservative.
15.6.5.4.3 Conclusions
15.6.5.4.3.1 Filter Loadings
No recirculating or single-pass filters are used for fission product cleanup
and control within the containment following a postulated LOCA. The only ESF
filtration systems expected to be operating under post-LOCA conditions are the
control room HVAC system and the auxiliary building emergency exhaust
filtration system.
Activity loadings on the control room charcoal adsorbers are based on the
flowrate through the adsorber, the concentration of activity at the adsorber
inlet, and the adsorber efficiency. Based on the radioactive iodine release
assumptions previously described, the assumption that 25 percent of the core
inventory of isotopes I-127 and I-129 is available for release from the
containment atmosphere and the assumption that the charcoal adsorber is 100
percent efficient, the calculated filter loadings are in accordance with
Regulatory Guide 1.52, which limits the maximum loading to 2.5 mg of iodine per
gram of activated charcoal.
15.6-37 Rev. 29 WOLF CREEK 15.6.5.4.3.2 Doses to a Receptor at the Exclusion Area Boundary
and Low Population Zone Outer Boundary
The potential radiological consequences resulting from the occurrence of the
postulated LOCA have been conservatively analyzed, using assumptions and models
described in previous sections.
The total-body dose due to immersion and the thyroid dose due to inhalation
have been analyzed for the 0-2 hour dose at the exclusion area boundary and for
the duration of the accident at the LPZ outer boundary. The results are listed
in Table 15.6-5. The resultant doses are within the guideline values of 10 CFR
100.
15.6.5.4.3.3 Doses to Control Room Personnel
Radiation doses to control room personnel following a postulated LOCA are based
on the ventilation, cavity dilution, and dose model discussed in Section 15A.3.
Control room personnel are subject to a total-body dose due to immersion and a
thyroid dose due to inhalation. These doses have been analyzed, and are
provided in Table 15.6-8. The resultant doses are within the limits
established by GDC-19.
15.6.6 A NUMBER OF BWR TRANSIENTS
This section is not applicable to WCGS.
15.
6.7 REFERENCES
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NUREG/CR-3046.
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- 3. Liles, D. R., et al., 1981, "TRAC-PD2, An Advanced Best-Estimate Computer Program for Pressurized Water Reactor Loss-of-Coolant Accident Analysis,"
NUREG/CR-2054.
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- 5. Dederer, S. I., et al., 1988, "Westinghouse Large-Break LOCA Best-Estimate Methodology - Volume 2: Application to Two-Loop PWRs Equipped with Upper Plenum Injection - Addendum 1: Responses to NRC Questions," WCAP-10924-P-A, Revision 2.
- 6. Bajorek, S. M., et al., 1998, "Code Qualification Document for Best-Estimate LOCA Analysis," WCAP-12945-P-A, Volume 1, Revision 2 and Volumes 2 through 5, Revision 1, and WCAP-14747 (Non-Proprietary).
- 7. Bordelon, F. M., et al., "LOCTA-IV Program: Loss-of-Coolant Transient Analysis," WCAP-8301 (Proprietary) and WCAP-8305 (Non-Proprietary), June 1974.
- 8. Thurgood, M. J., et al., 1980, "COBRA-TF Development," 8th Water Reactor Safety Information Meeting.
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- 12. Lee, N. et al., "Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP Code," WCAP-10054-P-A (Proprietary), August 1985.
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Loop and COSI Condensation Model, "WCAP-10054-P-A, Addendum 2, Revision 1, July 1977.
- 14. Special Report NS-NRC-85-3025(NP), "BART-WREFLOOD Input Revision." 15. Information Report from W.J. Dircks to the Commissioners, "Emergency Core Cooling System Analysis Methods," SECY-83-472, November 17, 1983.
- 16. "Best Estimate Calculations of Emergency Core Cooling System Performance,"
Regulatory Guide 1.157, USNRC, May 1989.
- 17. Salvatori, R., "Westinghouse ECCS - Plant Sensitivity Studies," WCAP-8340 (Proprietary) and WCAP-8356 (Non-Proprietary), July 1974.
- 18. Deleted
- 19. Deleted
- 20. WCAP-15704, Control Rod Insertion Following a Cold Leg LOCA, Generic Analyses for 3-Loop and 4-Loop Plants, October, 2001.
- 21. DiNunno, J. J., et al., "Calculation of Distance Factors for Power and Test Reactor Sites," TID-14844, Division of Licensing and Regulation, AEC, Washington, D.C., 1962.
- 22. USNRC NUREG-0409, "Iodine Behavior in a PWR Cooling System Following a Postulated Steam Generator Tube Rupture Accident," by Postma A. K. and Tam
P. S., dated January 1978.
- 23. NEI 04-07, Rev. 0, "Pressurized Water Reactor Sump Performance Evaluation Methodology" December 2004, Volume 1 and Volume 2.
- 24. EPA Federal Guidance Report No. 11, 1988, "Limiting Values of Radionuclide Intake and Air Concentration and dose Conversion Factors for Inhalation, Submersion, and Ingestion"
- 25. EPA Federal Guidance Report No. 12, 1993, "External Exposure to Radionuclides in ait, Water, and Soil"
- 26. Boyack, B., et. al., 1989, "Quantifying Reactor Safety Margins: Application of Code Scaling Applicability and Uncertainty (CSAU) Evaluation Methodology to a Large Break Loss-of-Coolant-Accident,"
NUREG/CR-5249.
- 27. Ivey J. S., Young M. Y., "Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting," WCAP-13451, October 1992. 28. Foster J. P. et al., "Westinghouse Improved Performance Analysis and Design Model (PAD 4.0)," WCAP-15063-P-A, Revision 1 with Errata (Proprietary), July 2000.
- 29. Gresham, J.A. et al., "Submittal of "Westinghouse Report for Changes to Heat Transfer Multiplier Uncertainty Distributions Used in the Approved BE LBLOCA Methodology" (Proprietary/Non-Proprietary)," LTR-NRC-14-1, January 2014. 15.6-39 Rev. 29 WOLF CREEK TABLE 15.6-1 TIME SEQUENCE OF EVENTS FOR INCIDENT WHICH RESULTS IN A DECREASE IN REACTOR COOLANT INVENTORY Time Accident Event (sec)Inadvertent opening of a pressurizer safety valve Safety valve opens fully 0.01 Overtemperature DT reactor trip setpoint 26.7 reached Turbine Trip 29.2 Steam generator tube rupture:
Failed-open auxiliary
feedwater control valve and safety valve Tube Rupture Occurs 0.0 Reactor Trip Signal 153.9 Reactor Trip (Rod Motion) 155.9 Auxiliary Feedwater Injection 183.9 Safety Injection Signal 204.1 Safety Injection (Pump Start) 219.1 Terminate Auxiliary Feedwater 684.1 to Faulted SG by closing unfailed AL-HV valve Terminate Auxiliary Feedwater 1284.1 to Faulted SG by locally closing failed AL-HV valve Initiate RCS Cooldown 2004.1 Terminate RCS Cooldown 2388.2 Water Relief Through SG Safety 2692.0 Valve Initiate RCS Depressurization 2868.2 Terminate RCS Depressurization 3032.8 Terminate Safety Injection 3334.0 (except 1 CCP) Throttle CCP flow to 100 gpm 3932.8 Establish Letdown 4832.8 Pressure Equalization 6214.9 Rev. 22 WOLF CREEK TABLE 15.6-1 (sheet 2) Time Accident Event (sec)Steam generator tube rupture: Failed-open automatic relief valve Tube Rupture Occurs 0.0 Reactor Trip, RCP Trip 143.0 Faulted ARV Fails Open 145.3 MFIV Closure Begins 145.0 MFIV Closure Ends 160.0 Safety Injection (Pump Start) 315.7 Identify/Isolate Faulted SG 1582.7 Initiate RCS Cooldown 3376.7 Terminate RCS Cooldown 3923.9 Initiate RCS Depressurization 4259.9 Terminate RCS Depressurization 4525.5 Terminate Safety Injection 5113.8 Pressure Equalization ~6000.0 Rev. 22 WOLF CREEK TABLE 15.6-2 PARAMETERS USED IN EVALUATING THE RADIOLOGICAL CONSEQUENCE OF THE CVCS LETDOWN LINE RUPTURE OUTSIDE OF CONTAINMENT
I. Source Data
- a. Core power level, MWt 3,565
- b. Reactor coolant iodine Dose equivalent of activity 1.0 Ci/gm of I-131
- c. Reactor coolant noble gas Based on 1-percent activity failed fuel. See Table 11.1-5.
II. Atmospheric Dispersion Factors See Table 15A-2.
III. Activity Release a. Break flow rate, gpm 444 b. Duration, secs 1810 c. Fraction of iodine activity in the spill that is
airborne 0.10 d. Activity released to the environment Isotope 0-2 hr (Ci)
I-131 3.70 I-132 3.89 I-133 6.47 I-134 8.47E-01 I-135 3.72 Xe-131m 1.73E+02 Xe-133m 2.71E+02 Xe-133 1.47E+04 Xe-135m 1.92E+01 Xe-135 4.89E+02 Xe-137 3.39 Xe-138 2.52E+01 Kr-83m 2.59E+01 Kr-85m 1.11E+02 Kr-85 4.76E+02 Kr-87 6.65E+01 Kr-88 2.05E+02 Kr-89 1.58
Rev. 25 WOLF CREEK TABLE 15.6-3 RADIOLOGICAL CONSEQUENCES OF A CVCS LETDOWN LINE BREAK OUTSIDE OF CONTAINMENT
Doses (rem) Exclusion Area Boundary (0-2 hr) Thyroid, 3.91e-1 Whole body 4.43e-2
Low Population Zone Outer Boundary (duration) Thyroid, 5.22e-2 Whole body 5.91e-3
Rev. 25
WOLF CREEK Table 15.6-4 PARAMETERS USED IN EVALUATING THE RADIOLOGICAL CONSEQUENCES OF A STEAM GENERATOR TUBE RUPTURE WITH FORCED OVERFILL I. Source Data a. Core power level, MWt 3636.3 (1)b. Steam generator tube leakage, gpm 1 (2)c. Reactor coolant iodine activity: 1. Case 1 Pre-accident iodine spike per Standard Review Plan 15.6.3. A pre-accident reactor transient
has occurred which raised the
primary coolant I-131
equivalent concentration to the
maximum value permitted by
Technical Specifications (60 Ci/gm).2. Case 2 Accident initiated iodine spike per Standard Review Plan
15.6.3. An iodine spike occurs
concurrently with reactor trip
where the release rate from the
fuel rods increases to a value
335 time greater than the release rate corresponding to the I-131 equivalent
concentration at the equilibrium value (1 Ci/gm)stated in the Technical Specifications.d. Reactor coolant noble Based on 1% failed fuel as gas activity provided in USAR Table 11.1-5. e. Secondary system Dose equivalent of 0.1 Ci/gminitial activity of I-131 f. Reactor coolant mass, lbs 4.964E+5 g. Steam generator mass (each), lbs 1. Water 9.884E+4 2. Steam 8.269E+3 h. Offsite power Lost at reactor trip Rev. 22 WOLF CREEK Table 15.6-4 (Sheet 2) i. Primary-to-secondary Break flow continues throughout leakage duration the transient, due to primary-secondary pressure inequalities, although most of the flow is terminated beyond the end of the second depressurization at approximately 6200 seconds (3).II. Atmospheric Dispersion Factor The atmospheric dispersion factors used are the same as those listed in USAR Table
15A-2.III. Activity Release Data a. Faulted steam generator 1. Reactor coolant discharged 195,371 to steam generator, lbs 2. Flashed reactor coolant Discussion below The fraction of the primary-to-secondary leakage that flashes to steam is defined as, X(t), where h avg (t) - h f (t) X(t) = ___________________ h g (t) - h f (t)and where h g(t) = saturated vapor specific enthalpy corresponding to the faulted steam generator water temperature, h f(t) = saturated liquid specific enthalpy corresponding to the faulted steam generator water temperature. The value h avg (t) is the average specific enthalpy and is defined as: [G HL (t)*h HL (t)] + [G CL (t)*h CL (t)] h avg = _____________________________________ G HL (t) + G CL (t)Where h HL(t) = specific enthalpy of the fluid from the hot leg, h CL(t) = specific enthalpy of the fluid from the cold leg, Rev. 22 WOLF CREEK Table 15.6-4 (sheet 3) G HL(t) = leakage flow from the hot leg to the faulted steam generator, G CL(t) = leakage flow from the cold leg to faulted steam generator. 3. Iodine partition factor 1.0 for flashed fraction of reactor coolant 4. Steam release to atmosphere, lbs 0-2 hours 140,406 (4)2 hour-RHR cut-in 120,960 (4)conditions5. Iodine carryover factor 0.01 for the non-flashed fraction of reactor coolant that mixes with the initial iodine activity in the steam generator b. Intact steam generators 1. Primary-to-secondary 4004 (2)leakage, lbs 2. Flashed reactor coolant, 0 percent3. Feedwater flow rate, lbs 0-2 hours 1,020,231 2 hours-RHR cut-in 280,800 conditions4. Steam release to atmosphere, lbs 0-2 hours 309,069 2-hours-RHR cut-in 299,520 conditions5. Iodine carryover factor 0.01 6. Transient end time The WCNOC analysis to force SGTR steam generator overfilling was carried out until RHR cut-in conditions
were achieved at 28,800 seconds.Rev. 22 WOLF CREEK Table 15.6-4 (sheet 4) c. Steam release from the 19,334 turbine-driven AFW pump turbine, lbs IV Dose Conversion Factors Nuclide Whole Body Thyroid Rem-m 3/Ci-sec Rem/Ci I-131 6.73E-02 1.08E+06 I-132 4.14E-01 6.44E+03 I-133 1.09E-01 1.80E+05 I-134 4.81E-01 1.07E+03 I-135 2.95E-01 3.13E+04 Kr-83m 5.55E-06 NA Kr-85m 2.77E-02 NA Kr-85 4.40E-04 NA Kr-87 1.52E-01 NA Kr-88 3.77E-01 NA Kr-89 3.23E-01 NA Xe-131m 1.44E-03 NA Xe-133m 5.07E-03 NA Xe-133 5.77E-03 NA Xe-135m 7.55E-02 NA Xe-135 4.40E-02 NA Xe-137 3.03E-02 NA Xe-138 2.13E-01 NA Rev. 22 WOLF CREEK Table 15.6-4 (sheet 5) Notes:1. This value is 102% of the guaranteed core thermal power output. This power level was chosen to maximize steam generator overfill, and thus the radiological consequences resulting from the overfill were calculated
from the results of this model. 2. A constant 1 gpm primary-to-secondary leakage with an assumed density of 62.4 lbm/ft 3 , is assumed to occur to the unaffected steam generators, for the duration of the event. 3. Steam generator overfill was forced by delaying the termination of safety injection to provide enough liquid in the faulted steam generator steam line to force safety valve opening and liquid relief. The extended SI flow time caused the primary pressure to remain high, thus the primary/secondary pressure remained unequal and allowed for break flow to
continue for an extended period of time. 4. The SGTR with Forced Overfill analysis assumed that at liquid relief through the faulted steam generator steam line safety valve, the valve
would fail open with an effective flow area of 5%, with consequent
continued secondary blowdown until RHR cut-in conditions were reached. Rev. 22 WOLF CREEK TABLE 15.6-5 RADIOLOGICAL CONSEQUENCES OF A STEAM GENERATOR TUBE RUPTURE Case 1 Dose (rem) Exclusion Area Boundary (0-2 hr) Thyroid 51.769 Whole body 0.226 Low Population Zone (duration) Thyroid 7.192 Whole body 0.034 Case 2 Exclusion Area Boundary (0-2 hr) Thyroid 22.797 Whole body 0.132 Low Population Zone (duration) Thyroid 4.825 Whole body 0.025 Case 1 - Pre-accident iodine spike per SRP 15.6.3 Case 2 - Concurrent iodine spike per SRP 15.6.3 Rev. 23 WOLF CREEK TABLE 15.6-6 PARAMETERS USED IN EVALUATING THE RADIOLOGICAL CONSEQUENCES OF A LOSS-OF-COOLANT-ACCIDENTI. Source Data a. Core power level, MWt 3,565 b. Burnup, full power days per cycle 510
- c. Percent of core activity initially airborne in the containment 1. Noble gas 100 2. Iodine 25 d. Percent of core activity in containment sump @ 0.47 hours 1. Noble gases 0 2. Iodine 50 e. Core inventories Table 15A-3 f. Iodine distribution, percent 1. Elemental 91 2. Organic 4
- 3. Particulate 5 II. Atmospheric Dispersion Factors See Table 15A-2 III. Activity Release Data a. Containment leak rate, volume percent/day
- 1. 0-24 hours 0.20 2. 1-30 days 0.10 b. Percent of containment leakage that is unfiltered 100 c. Credit for containment sprays 1. Spray iodine removal constants (per hour) a. Elemental 10.0 b. Organic 0.0 c. Particulate 0.45 Rev. 23 WOLF CREEK TABLE 15.6-6 (Sheet 2) 2. Maximum iodine decontamination factors for the containment atmospherea. Elemental 100 b. Organic 0
- c. Particulate 100 3. Sprayed volume, percent 85 4. Unsprayed volume, percent 15 5. Sprayed-unsprayed mixing rate, CFM 85,000 6. Containment volume, ft 3 2.5E+6 d. Activity released to containment Isotope Curies I-131 2.37E+7 I-132 3.43E+7
I-133 4.88E+7
I-134 5.38E+7 I-135 4.58E+7 Xe-131m 1.01E+6
Xe-133m 6.06E+6
Xe-133 1.95E+8 Xe-135m 3.77E+7 Xe-135 4.70E+7
Xe-137 1.71E+8 Xe-138 1.64E+8
Kr-83m 1.24E+7
Kr-85m 2.67E+7
Kr-85 1.02E+6 Kr-87 5.16E+7
Kr-88 7.28E+7
Kr-89 8.94E+7 e. ECCS recirculation leakage 1. Leak rate (0.47 hours-30 day), gpm 2.0 Rev. 23 WOLF CREEK TABLE 15.6-6 (Sheet 3) 2. Iodine inventory in sump @ 0.47 hour, curies I-131 4.72E+7 I-132 5.94E+7 I-133 9.60E+7 I-134 7.41E+7 I-135 8.71E+7 3. Sump volume, gal. 460,000 4. Fraction iodine airborne 0.1 5. ESF filter efficiency, % 90.0 IV. Control room parameters Tables 15A-1 and 15A-2 Rev. 23 WOLF CREEK TABLE 15.6-7 DESIGN COMPARISON TO THE REGULATORY POSITIONS OF REGULATORY GUIDE 1.4 "ASSUMPTIONS USED FOR EVALUATING THE POTENTIAL RADIOLOGICAL CONSEQUENCES OF A LOSS OF COOLANT ACCIDENT FOR PRESSURIZED WATER REACTORS," REVISION 2, JUNE 1974 Regulatory Guide 1.4 Position Design
- 1. The assumptions related to the release of radioactive material from
the fuel and containment are as
follows: a. Twenty-five percent of the 1a. Complies. equilibrium radioactive iodine in-
ventory developed from maximum full
power operation of the core should
be assumed to be immediately avail-
able for leakage from the primary
reactor containment. Ninety-one
percent of this 25 percent is to be
assumed to be in the form of elemental
iodine, 5 percent of this 25 percent in the form of particulate iodine, and 4 percent of this 25 percent in
the form of organic iodides.
- b. One hundred percent of equi- 1b. Complies.
librium radioactive noble gas inven-
tory developed from maximum full
power operation of the core should
be assumed to be immediately avail-
able for leakage from the reactor containment.
- c. The effects of radiological 1c. Complies. Credit decay during holdup in the contain- for radioactive
ment or other buildings should be decay is taken taken into account. until the activity
is assumed to be
released.
- d. The reduction in the amount 1d. Complies.
S ee Table of radioactive material available for 15.6-6 for reduction leakage to the environment by con- taken.
tainment sprays, recirculating filter
systems, or other engineered safety
features may be taken into account, but the amount of reduction in con-centration of radioactive materials should be evaluated on an individual
case basis. Rev. 0 WOLF CREEK TABLE 15.6-7 (S heet 2) Regulatory Guide 1.4 Position Designe. The primary reactor contain- 1e. Complies. ment should be assumed to leak at the leak rate incorporated or to be incor-
porated as a technical specification
requirement at peak accident pressure
for the first 24 hours, and at 50
percent of this leak rate for the
remaining duration of the accident.
Peak accident pressure is the
maximum pressure defined in the
technical specifications for con-tainment leak testing. 2. Acceptable assumptions for atmo- 2a. Complies. Atmo- spheric diffusion and dose conversion spheric dispersion are: factors were cal-
- a. The 0-8 hour ground level culated based on the release concentrations may be reduced onsite meteorologi-by a factor ranging from one to a cal measurement pro- maximum of three (see Figure 1) for grams described in additional dispersion produced by the S ection 2.3.
turbulent wake of the reactor building
in calculating potential exposures.
The volumetric building wake correc-tion, as defined in section 3-3.5.2
of Meteorology and Atomic Energy 1968, should be used only in the 0-8 hour
period; it is used with a shape factor
of 1/2 and the minimum cross-sectional
area of the reactor building only.
- b. No correction should be made 2b.
S ame as 2a above. for depletion of the effluent plume of
radioactive iodine due to deposition
on the ground, or for the radiological
decay of iodine in transit.
- c. For the first 8 hours, the 2c. Complies.
S ee Table breathing rate of persons offsite 15A-1 should be assumed to be 3.47 x 10 -4 cubic meters per second. From 8 to 24 hours following the accident, the
breathing rate should be assumed to be 1.75 x 10 -4 cubic meters per second. After that until the end of the accident, the breathing rate should be assumed to be 1.75 x 10 -4 cubic meters per second. After that until the end of the accident, the rate should be assumed to be 2.32 x 10 -4 cubic meters Rev. 1 WOLF CREEK TABLE 15.6-7 (S heet 3) Regulatory Guide 1.4 Position Design per second. (These values were devel-oped from the average daily breathing
rate [2 x 10 7 cm3/day] assumed in the report of ICRP, Committee II-1959.)
- d. The iodine dose conversion 2d. The dose conversion
factors are given in ICRP Publication factors provided in
2, Report of Committee II, "Permis- Regulatory Guide
sible Dose for Internal Radiation," 1.109 are used.
1959. S ee Table 15A-4.
- e. External whole body doses 2e. The dose factors
should be calculated using "Infinite given in Regulatory
Cloud" assumptions, i.e., the dimen- Guide 1.109, for sions of the cloud are assumed to be noble gases; for large compared to the distance that iodine whole body
the gamma rays and beta particles dose factors with
travel. " S uch a cloud would be con- 5cm body tissue sidered an infinite cloud for a re- attenuation; and for ceptor at the center because any beta-skin dose
additional [gamma and] beta emitting factors with credit
material beyond the cloud dimensions for attenuation
would not alter the flux of [gamma in the dead skin
rays and] beta particles to the re- layer, are used.
ceptor" (Meteorology and Atomic S ee Table 15A-4. Energy, S ection 7.4.1.1-editorial additions made so that gamma and beta emitting material could be
considered). Under these conditions the rate of energy absorption per unit volume is equal to the rate of
energy released per unit volume.
For an infinite uniform cloud con-
taining curies of beta radioactivity per cubic meter the beta dose in air
at the cloud center is: Doo = 0.457 E _ The surface body dose rate from beta emitters in the infinite cloud can be
approximated as being one-half this amount (i.e., Doo = 0.23 E_)For gamma emitting material the dose rate in air at the cloud center is: x D 507.0 From a semi-infinite cloud, the gamma
dose rate in air is: x D 25.0 Rev. 19 WOLF CREEK TABLE 15.6-7 (S heet 4) Regulatory Guide 1.4 Position Design Where D oo= beta dose rate from an infinite cloud (rad/sec) D oo= gamma dose rate from an infinite cloud (rad/sec) E_ = average beta energy per disintegration (Mev/dis) E_ = average gamma energy per disintegration (Mev/dis) = concentration of beta or gamma emitting isotope in the cloud (curie/m 3)f. The following specific 2f.1 S ee response to 2e. assumptions are acceptable with re-spect to the radioactive cloud dose
calculations:
(1) The dose at any dis-
tance from the reactor should be
calculated based on the maximum con-
centration in the plume at that dis-
tance taking into account specific
meteorological, topographical, and
other characteristics which may affect
the maximum plume concentration.
These site related characteristics
must be evaluated on an individual
case basis. In the case of beta
radiation, the receptor is assumed to
be exposed to an infinite cloud at
the maximum ground level concentra-
tion at that distance from the reactor.
In the case of gamma radiation, the
receptor is assumed to be exposed to
only one-half the cloud owing to the
presence of the ground. The maximum
cloud concentration always should be
assumed to be at ground level.
(2) The appropriate average 2f.2 S ee response to 2e.
beta and gamma energies emitted per
disintegration, as given in the Table
of Isotopes, S ixth Edition, by C. M. Lederer, J. M. Hollander, I. Perlman; Rev.1 WOLF CREEK TABLE 15.6-7 (S heet 5) Regulatory Guide 1.4 Position Design University of California, Berkeley; Lawrence Radiation Laboratory;
should be used.
- g. The atmospheric diffusion model should be as follows:
(1) The basic equation for 2g.1 S hort-term accident atmospheric diffusion from a ground atmospheric dispersion level point source is: factors were calculated
based on onsite /Q = 1 u y meteorological data measurement programs
described in S ection Where 2.3. These factors are for ground level = the short term average releases and are centerline value of the based on Regulatory
ground level concentration Guide 1.145 method-(curie/meter
- 3) ology and represent Q = amount of material re- the worst of the leased (curie/sec) 5 percent site u = windspeed (meter/sec) meteorology and the y = the horizontal standard 0.5 percent worst deviation of the plume sector meteorology.
(meters) [
S ee Figure V-1, Page 48, Nuclear S afety , June 1961, Volume 2, Number 4, "Use of Routine Meteororo-
logical Observations for Estimating Atmospheric Dis-
persion," F.A. Gifford, Jr.] z = the vertical standard devi-ation of the plume (meters)
[
S ee Figure V-2, Page 48, Nuclear S afety , June 1961, Volume 2, Number 4, "Use of Routine Meteorological Obser-
vations for Estimating At-mospheric Dispersion," F.A. Gifford, Jr.] (2) For time periods of 2g.2 S ee response to 2g.1 greater than 8 hours the plume should above.
be assumed to meander and spread
uniformly over a 22.5° sector. The resultant equation is: /Q = 2.032 z ux Rev. 1 WOLF CREEK TABLE 15.6-7 (S heet 6) Regulatory Guide 1.4 Position Design Where x = distance from point of re-lease to the receptor; other
variables are as given in
g(1).
(3) The atmospheric dif- 2g.3 S ee response to 2g.1 fusion model 2 for ground level re- above.
leases is based on the information in the following table. Time Following Accident Atmospheric Conditions 0-8 hours Pasquill Type F, wind-speed 1 meter/sec, uni-
form direction 8-24 hours Pasquill Type F, wind-speed 1 meter/sec, vari-
able direction within a
22.5° sector 1-4 days (a) 40% Pasquill Type D, windspeed 3 meter/sec
(b) 60% Pasquill Type F, windspeed 2 meter/sec
(c) wind direction vari-
able within a 22.5º sector 4-30 days (a) 33.3% Pasquill Type C, windspeed 3 meter/sec
(b) 33.3% Pasquill Type D, windspeed 3 meter/sec
(c) 33.3% Pasquill Type F, windspeed 2 meter/sec
(d) Wind direction 33.3%
frequency in a 22.5°
sector (4) Figures 2A and 2B give 2g.4 S ee response to 2g.1 the ground level release atmospheric above. diffusion factors based on the para-
meters given in g(3). Rev. 0 WOLF CREEK TABLE 15.6-8 Radiological Consequences of a Loss-of-Coolant-Accident
Total Reported Doses (rem) Regulatory Limits (rem) I. Exclusion Area Boundary (0-2 hr) Thyroid 61.95 300 Whole body 1.18 25 II. Low Population Zone Outer Boundary(0-30 day) Thyroid 95.59 300 Whole body 0.41 25 III. Control Room (0-30 day)
Thyroid 17.99 30 Whole body 0.15 5 Beta-skin 3.29 30
Rev. 26
WOLF CREEK TABLE 15.6-9 Major Plant Parameter Assumptions Used in the BELOCA Analysis for Wolf Creek Parameter Value Plant Physical Description SG Tube Plugging 10% Plant Initial Operating Conditions Reactor Power 3565 MWt (+ 2% uncertainty) Peaking Factors See Table 15.6-9B Axial Power Distribution See Figure 15.6-22 Fluid Conditions T AVG 570.7 - 4.0 o F T AVG 588.4 + 4.0 o F Pressurizer Pressure 2250 - 50 psia P RCS 2250 + 50 psia Reactor Coolant Flow 90,324 gpm/loop Accumulator Temperature 50 o F T ACC 120 o F Accumulator Pressure 582.8 psia P ACC 696.6 psia Accumulator Water Volume 818 ft 3 V ACC 881 ft 3 Accumulator Boron Concentration 2300 ppm Accident Boundary Conditions Single Failure Assumptions Loss of one ECCS train Safety Injection Flow See Table 15.6-13 Safety Injection Temperature 37 o F TSI 120 o F Safety Injection Initiation Delay Time 27 sec. (with offsite power) 39 sec. (without offsite power) Containment Pressure Bounded (minimum); see Figure 15.6-20
Rev. 29 WOLF CREEK TABLE 15.6-9A Input Parameters Used in the Small LOCA Analysis License Core Power 1 (100% power) (MWth) 3565 Peak Linear Power 1 (KW/ft) 13.909 Total Peaking Factor [F T Q]2.50 Axial Peaking Factor [F z]1.5151 Hot Channel Enthalpy Rise Factor [FH]1.65 Maximum Assembly Average Power[P HA]1.469 Power Shape Figure 15.6-47 Fuel Type/Assembly Array 17x17 Standard RFA-2 Zirlo+2, 1.5X IFBA, IFM Accumulator Water Volume (ft 3/accumulator) 850 Accumulator Tank Volume (ft 3/accumulator) 1350 Accumulator Gas Pressure, Minimum (psia) 583 Safety Injection Pumped Flow Figures 15.6-46 & 15.6-46A, Tables 15.6-14 & 15.6-14A Containment Parameters See Section 6.2.1.5 Initial Loop Flow (gpm/loop) 90324 Nominal Vessel Average Temperture (F) 570.7 -588.4 Reactor Coolant Pressure 2 (psia) 2300 Steam Pressure (psia) 938.89 Steam Generator Tube Plugging Level (%) 10 AFW Flow Rate (gpm/steam generator) 210 -250 Notes:(1) Two percent is added to this power to account for calorimetric uncertainty. Reactor coolant pump heat is not modeled in LOCA Analysis.(2) This pressure includes 50 psi for measurement uncertainty. Rev. 22 WOLF CREEK TABLE 15.6-9B Summary of Peaking Factor Burndown Analyzed by the Best-Estimate Large-Break LOCA Analysis for Wolf Creek Hot Rod Burnup (MWD/MTU) FdH (with uncertainties) FQ Transient (with uncertainties) FQ Steady-state (without uncertainties) 0 1.65 2.50 2.121 30000 1.65 2.50 2.121 60000 1.525 2.25 1.906 62000 1.525 2.25 1.906 Note: Full Table is used for 2 nd Cycle, values at Burnup=0 were utilized for 1 st Cycle Rev. 29 WOLF CREEK TABLE 15.6-10 Wolf Creek Best Estimate Large Break Sequence of Events for the Limiting PCT Case in seconds Start of Transient
0.0 Safety
Injection Signal 6.0 Accumulator Injection Begins 10.0 End of Blowdown 21.0 Bottom of Core Recovery 30.0 Accumulator Begins to Empty 34.0 Safety Injection Begins 45.0 PCT Occurs 70.0 Quench Time (WCOBRA/TRAC) 310.0 End of Transient 350.0
Rev. 29 WOLF CREEK TABLE 15.6-10 (Sheet 2)
Deleted
Rev. 29 WOLF CREEK TABLE 15.6-10A Time Sequence of Events for Small Break LOCA Break Size 2-inch 3-inch 4-inch 6-inch 8.75-inch Break Initiation 0 0 0 0 0 Reactor Trip Signal 112.02 40.29 22.75 9.71 7.16 Safety Injection Signal 121.62 48.85 30.40 15.08 8.77 Safety Injection Begins (1)160.62 87.85 69.40 54.08 47.77 Loop Seal Clearing Occurs (2)1166 418 248 55 17 Accumulator Injection N/A N/A 954 385 175 Top of Core Uncovered N/A 875 713 422 N/A Peak Clad Temperature Occurs N/A 1236.6 1033.5 462.6 N/A Top of Core Recovered (3)2233 1401 470 (3)RWST Low Level (4)1980 1943 1908 1793 1547 Notes:(1) Safety Injection (SI) is assumed to begin 39 seconds after the SI signal.(2) Loop seal clearing is considered to occur when the broken loop seal vapor flow rate is sustained above 1 lbm/s (3) For the cases where core recovery is greater than the transient time, basis for transient termination can be concluded based on some or all of the following: (1) The RCS system pressure is decreasing which will increase SI flow, (2) Total RCS system mass is increasing due to SI flow exceeding break flow, and (3) Core mixture level has begun to increase and is expected to continue for the remainder of the accident.(4) The analysis assumes minimum usable RWST volume (239, 324 gal) before the low-1 RWST water level signal for switchover to cold leg recirculation is reached. Rev. 22 WOLF CREEK TABLE 15.6-11 Wolf Creek Best Estimate Large Break LOCA Results 10 CFR 50.46 Requirement Value Criteria 95/95 PCT (o F) 1900 < 2200 95/95 LMO (1) (%) 4.21 < 17 95/95 CWO (2) (%) 0.1352 < 1 Notes: (1) LMO - Local Maximum Oxidation (2) CWO - Core Wide Oxidation Rev. 29
WOLF CREEK TABLE 15.6-12 SMALL BREAK LOCA RESULTS FUEL CLADDING DATA Break Size (in) 2 (1)3 4 4 (w/Annular Pellets)6 8.75 (3)PCT ( F)895.8 935.5 935.6 621.7 PCT Elevation (ft) 10.75 11.0 11.0 11.5 Hot Rod Burst Time (sec) No Burst No Burst N o Burst No Burst Hot Rod Burst Elevation (ft)(2)N/A N/A N/A N/A Max. Local transient ZrO 2 Reaction (%) 0.01 0.01 0.01 0.01 Max. Local ZrO 2 Elev. (ft) 11.00 11.00 11.00 11.50 Core-Wide Avg. ZrO 2 (%) N/A1.01.01.01.0 N/A Notes:(1) There is no core uncovery for the 2-inch case. (2) None of the SBLOCTA calculations exhibited rod burst (hot rod or hot assembly average rod). (3) The core only uncovers for a minimal time and does not warrant SBLOCTA calculations. Rev. 22 WOLF CREEK TABLE 15.6-13 Safety Injection Flow for BE Large Break LOCA Analysis RCS Pressure (psig) HHSI RCS P ressure (psig) IHSI and RHR Combined Injecting (gpm) Intact Loops Spilling (gpm) Broken Loop Injecting (gpm) Intact Loops Spilling (gpm) Broken Loop 0 287 103 0 3563 1209 20 285 104 20 3285 1295 40 283 105 40 2992 1379 60 281 106 60 2679 1462 80 279 107 80 2340 1543 100 277 108 100 1965 1625 120 274 109 120 1532 1709 140 272 110 140 989 1800 160 270 111 160 397 1875 180 268 112 180 393 1876 200 266 113 200 389 1876 300 255 117 300 369 1880 400 244 122 400 347 1883 500 232 126 500 325 1887 600 217 190 600 302 1890 700 197 200 700 277 1894 800 177 210 800 250 1898 900 156 219 900 220 1937 1000 135 229 1000 180 1943 1100 113 238 1100 135 1949 1200 90 247 1200 81 1956 1300 67 256 1300 6 1964 1400 42 265 1400 0 1964 1500 15 274 - - - 1600 0 280 - - -
Rev. 29 WOLF CREEK TABLE 15.6-14 Pumped Safety Injection (SI) Flow Rate Assumed for 2 - 6 Inch Small Breaks Broken Loop SI Flows (Spill to RCS Pressure) CCP
- SIP*RHRP*RCS Pressure (psig)Injecting (gpm)Intact Loops Spilling (gpm)Broken Loop RCS Pressure (psig)Injecting (gpm)Intact Loops Spilling (gpm)Broken Loop RCS Pressure (psig)Injecting (gpm)Intact Loops Spilling (gpm)Broken Loop 0 317.48 112.59 0 444.82 154.97 0 2834.19 1075.76 100 309.44 109.74 100 429.33 149.57 20 2660.73 1009.97 200 301.32 106.87 200 413.26 143.97 40 2477.16 940.33 300 293.09 103.95 300 396.55 138.15 60 2280.95 865.91 400 284.76 101.00 400 379.11 132.07 80 2068.49 785.32 500 276.27 97.99 500 360.82 125.69 100 1834.31 696.50 600 267.61 94.92 600 341.54 118.98 120 1569.20 595.91 700 258.77 91.79 700 321.09 111.85 140 1254.38 476.48 800 249.72 88.58 800 299.20 104.22 150 1065.81 404.92 900 240.41 85.29 900 275.52 95.97 155 959.33 364.53 1000 230.86 81.90 1000 249.49 86.90 160 839.61 319.10 1100 221.00 78.41 1100 220.21 76.69 170 534.36 203.24 1200 210.79 74.79 1200 185.98 64.77 175 295.67 112.61 1300 200.18 71.03 1300 142.84 49.74 180 0.00 0.00 1400 189.13 67.12 1400 72.76 25.32 1500 177.55 63.01 1420 40.00 13.91 1600 165.35 58.69 1440 0.00 0.00 1800 138.49 49.17 1500 0.00 0.00 2000 106.72 37.91 2235 55.68 19.82 2300 34.70 12.38 2350 11.76 4.22 2400 0.00 0.00*1 train operating Rev. 22 WOLF CREEK TABLE 15.6-14A Pumped Safety Injection (SI) Flow Rate Assumed for 8.75 inch Accumulator Line Break Broken Loop SI Flows (Spill to Containment Pressure, 0 psig)
CCP
- SIP*RHRP*RCS Pressure (psig)Injecting (gpm)Intact Loops Spilling (gpm)Broken Loop RCS Pressure (psig)Injecting (gpm)Intact Loops Spilling (gpm)Broken Loop RCS Pressure (psig)Injecting (gpm)Intact Loops Spilling (gpm)Broken Loop 0 317.48 112.59 0 444.82 154.97 0 2834.19 1075.76 100 301.07 122.40 100 424.60 159.61 20 2579.31 1163.27 200 284.72 131.75 200 403.66 164.22 40 2310.43 1248.78 300 268.39 140.72 300 381.93 168.80 60 2023.36 1333.04 400 252.01 149.36 400 359.28 173.35 80 1712.00 1416.88 500 235.50 157.73 500 335.54 177.90 100 1366.47 1501.38 600 218.82 165.85 600 310.53 182.44 120 967.94 1588.36 700 201.92 173.76 700 283.99 187.00 140 464.71 1683.57 800 184.73 181.49 800 255.56 191.59 150 186.62 1726.84 900 167.18 189.06 900 224.71 196.24 155 7.15 1751.62 1000 149.19 196.49 1000 190.63 200.98 160 0.00 1752.56 1100 130.67 203.80 1100 151.88 205.88 170 0.00 1752.56 1200 111.45 211.03 1200 105.54 211.07 175 0.00 1752.56 1300 91.40 218.18 1300 43.25 216.89 180 0.00 1752.56 1400 70.27 225.28 1380 0.00 220.15 1500 47.68 232.37 1400 0.00 220.15 1600 23.08 239.49 1650 9.73 243.09 1700 0.00 246.13 1800 0.00 250.38 2000 0.00 251.94*1 train operating Rev. 22 1.a,...----------------------, ::11,400 r------------------------, 1,ooo
..
- s. I aeo *** l**a n*'7* g*70
.. TIME Rev.12 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6*1 NUCLEAR POWER, PRESSURIZER PRESSURE AND REACTOR COOLANT AVERAGE TEMPERATURE FOR INADVERTENT OPENING OF A PRESSURIZER SAFETY VALVE 3.2 3.1 3 2.9 2.8 E 2.7 !§52.6 2.5 2.4 2.3 2.2 2.1 0 4 8 12 18 20 24 28 Time (seconds) Rev.12 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-2 DNBR TRANSIENT FOR INADVERTENT OPENING OF A PRESSURIZER SAFETY VALVE
Figure 15.6-3A
8001000120014001600 180020002200 2400 01000200030004000500060007000Time (seconds) Pressurizer Pressure (psia)Reactor TripInitiate SITerminate AFWInitiate RCS CooldownTerminate RCS CooldownInitiate DepressurizationTerminateDepressurizationTerminate SI (except ofr 1 CCP)Throttle CCP FlowEstablish Letdown
Rev. 25 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3A: PRESSURIZER PRESSURE TRANSIENT SGTR FORCED OVERFILL WITH STUCK-OPEN STEAM GENERATOR SAFETY VALVE 10020030040050060070001000200030004000500060007000Time (seconds) Faulted Loop RCS Temperature (F)Hot LegCold Leg REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3B: FAULTED LOOP RCS TEMPERATURE TRANSIENTS SGTR FORCED OVERFILL WITH STUCK-OPEN STEAM GENERATOR SAFETY VALVE 40045050055060065001000200030004000500060007000Time (seconds) Intact Loop RCS Temperatures (F)Hot LegCold Leg REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3C: INTACT LOOP RCS TEMPERATURE TRANSIENTS SGTR FORCED OVERFILL WITH STUCK-OPEN STEAM GENERATOR SAFETY VALVE 400500 600 7008009001000 110012001300 140001000200030004000500060007000Time (seconds)SG Pressure (psia)Reactor TripTerminate AFW toRuptured SGTerminate RCS CooldownInitiate RCS CooldownWater ReliefIntact SGRuptured SG REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3D: STEAM GENERATOR PRESSURE TRANSIENTS SGTR FORCED OVERFILL WITH STUCK-OPEN STEAM GENERATOR SAFETY VALVE 460480 500 520 54056058001000200030004000500060007000Time (seconds)SG Temperature (F)Terminate AFW toRuptured SGInitiate RCSCooldownTerminate RCSCooldownIntact SGRuptured SGReactor Trip REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3E: STEAM GENERATOR TEMPERATURE TRANSIENTS SGTR FORCED OVERFILL WITH STUCK-OPEN STEAM GENERATOR SAFETY VALVE 10 15 20 25 30 35 4001000200030004000500060007000Time (seconds) Pressurizer Water Level (ft)Initiate SIInitiate RCSCooldownTerminate RCSCooldownTerminate SIThrottel SI (except for 1 CCP)Establish Letdown REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3F: PRESSURIZER WATER LEVEL TRANSIENT SGTR FORCED OVERFILL WITH STUCK-OPEN STEAM GENERATOR SAFETY VALVE -200 02004006008001000 120001000200030004000500060007000Time (seconds) Faulted SG Steam Flow (lbm/sec) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3G: FAULTED STEAM GENERATOR STEAM FLOW TRANSIENT SGTR FORCED OVERFILL WITH STUCK-OPEN STEAM GENERATOR SAFETY VALVE 0 20 40 60 80100 120 14001000200030004000500060007000 Time (seconds) Faulted SG AFW Flow Rate (lbm/sec)ReactorTripIsolate AFW Ruptured SG (Closeunfailed AL-HV valve)Isolate AFW Ruptured SG (Close failed AL-HV valve REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3H: FAULTED STEAM GENERATOR AFW FLOW TRANSIENT SGTR FORCED OVERFILL WITH STUCK-OPEN STEAM GENERATOR SAFETY VALVE 0 5 10 15 20 25 30 35 40 45 5001000200030004000500060007000Time (seconds)Break Flow (lbm/sec)Initiate SITerminate AFW toRuptured SGInitiate RCS DepressurizationInitiate RCS CooldownTerminate SIThrottle CCP FlowEstablish LetdownTerminate RCSDepressurizationTerminate RCS cooldaown REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3I: FAULTED STEAM GENERATOR BREAK FLOW TRANSIENT SGTR FORCED OVERFILL WITH STUCK-OPEN STEAM GENERATOR SAFETY VALVE 2000250030003500 4000450050005500600001000200030004000500060007000Time (seconds) Faulted SG Mixture Volume (ft3) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3J: FAULTED STEAM GENERATOR MIXTURE VOLUME TRANSIENT SGTR FORCED OVERFILL WITH STUCK-OPEN STEAM GENERATOR SAFETY VALVE 2400 -*-Reactor Trip 2200 2000 ... ; 1800 e "' .. 1600 a. \ lnlUate St "' i 1400 1200 1000 800 0 1000 2000 / -Terminate Sl (except tor 1 CCP) Terminate RCS Cooldown / Terminate DepressuriZation 3000 4000 5000 6000 7000 Time (seconds) REV. 22 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3K: PRESSURIZER PRESSURE TRANSIENT SGTR W/ STUCK-OPEN ATMOSPHERIC RELIEF VALVE 700r----------------------------------------------------------. 600 500 Hot Leg e :I r! 8. 400 t/) u a: 300 \ \ . \? \___; 200 0 1000 2000 3000 4000 5000 6000 7000 Time (seconds) REV. 22 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3L: FAULTED LOOP RCS TEMPERATURE SGTR W/ STUCK-OPEN ATMOSPHERIC RELIEF VALVE
500 !!;: 550 e 3 I!! ! 500 " 450 Hot leg '. '\_____ . ./ \; Coldleg 0 1000 2000 3000 4000 5000 6000 7000 Time (seeonds) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3M: INTACT LOOP RCS TEMPERATURE TRANSIENT SGTR W/ STUCK-OPEN ATMOSPHERIC RELIEF VALVE 1400r--------------------------------------------------------------, 1300 1200 1100 s 1000 S: I!! :::1 900 ::1 e IL CJ 800 Ill 700 600 500 400 0 /Reactor Trip I I . Rup1Ured SG \ i 1000 I Tenninate RCS Intact SG f Cooldown -..... f----ARV lsolaled 2000 3000 4000 5000 6000 7000 nme(seconds) REV. 22 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3N: STEAM GENERATOR PRESSURE TRANSIENT SGTR W/ STUCK-OPEN ATMOSPHERIC RELIEF VALVE
560 540 !£ 520 l E {! 500 C) Ill 480 460 440 0 --Reactor Trip \ 1000 2000 3000 Terminate RCS Cool down Ruptured SG lntactSG 4000 5000 6000 7000 llme (seconds) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-30: STEAM GENERATOR TEMPERATURE TRANSIENT SGTR W/ STUCK-OPEN ATMOSPHERIC RELIEF VALVE 40.00 35.00 30.00 ........-Reactor Trip :: i 25.00 > !l J!l 20.00 j "' i 15.00 0.. 10.00 5.00 "-.Initiate Sl 0.00 0 1000 2000 Tenninate RCS Cooldown 3000 4000 5000 6000 7000 Time REV. 22 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3P: PRESSURIZER WATER LEVEL TRANSIENT SGTR W/ STUCK-OPEN ATMOSPHERIC RELIEF VALVE 1200 -1000 800 u .. "' 600 e g / ARVOpen ;:;:: E 400 ., !I !/) 200 0 1000 -200 l I ARV Isolated 2000 3000 4000 5000 6ooo 7Cpo Time (seconds) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-30: FAULTED STEAM GENERATOR STEAM FLOW TRANSIENT SGTR W/ OPEN ATMOSPHERIC RELIEF VALVE 100.,.-------------------------------,100 90 90 80 80 g 70 70 "' ';so l u: 50 c( :;: 40 AFW Flowrate ... 30 30 20 20 10 10 0 1000 2000 3000 4000 5000 -*60110
- 7000 Time (seconds)
REV. 22 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3R: FAULTED STEAM GENERA TOR AFW AND NR LEVEL TRANSIENT SGTR WI STUCK-OPEN ATMOSPHERIC RELIEF VALVE 50 40 u "' 1 30 .... ... .. ! Ill 20 10 / Terminate RCS Cooldown Terminate RCS / Depressurization 0 1000 2000 3000 4000 5000 6000 7000 Time (seconds) REV. 22 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3S: FAULTED STEAM GENERATOR TOTAL BREAK FLOW TRANSIENT SGTR W/ STUCK-OPEN ATMOSPHERIC RELIEF VALVE 5900 5400 4900 4400 .. E .: 3900 3400 i Cl (/) 2900 2400 1900 1400 +--...:::::::=:::;::::::::.. __ -,.----,-------.------r----r------1 0 1000 2000 3000 4000 5000 6000 7000 Time !seconds) REV. 22 WOLFCREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-3T: FAULTED STEAM GENERATOR MIXTURE VOLUME TRANSIENT SGTR WI STUCK-OPEN ATMOSPHERIC RELIEF VALVE R E V. 29 U P DA TE D S A FET Y ANA L Y S I S R E P O R T W O L F CREE K F IGU R E 15.6-5 EVA L UA T ION METHODO LOGYAND UN C E R T A I N T Y (C SAU)COD E S C A L I NG, A PP L I C A B I L I T Y , N 0 T R u M p L 0 . c T CORI PRIIIURI. CORI 'LOW. MIXTURI \.lVII.. AND 'VIL 11100 A IOWIII MIITORY 0 < TIMI < CORI CGVUID RGURE1i.M CODE INTERFACE DE8CIIIP110III FOR SMALL BREAK MODa . ' ' ... ,
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-7 HOTSPOT Cladding Temperature Transient and WC/T PCT for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-8 PCT Elevation for the Hot Rod for the Limiting RCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-9 Break Flow for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-10 Void Fraction in the Reactor Coolant Pumps for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-11 Vapor Flow in the Hot Assembly Channel for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-12 Pressurizer Pressure for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-13 Lower Plenum Collapsed Liquid Level for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-14 Accumulator Injection Flow for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-15 Safety Injection Flow (HHSI) for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-16 Safety Injection Flow (IHSI+RHR) for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-17 Downcomer Collapsed Liquid Level for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-18 Collapsed Liquid Level in Core Average Channel for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-19 Vessel Liquid Mass for the Limiting PCT Case
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-21 Analysis vs. Calculated Containment Backpressure
REV. 2 9 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-22 Wolf Creek BELOCA Analysis Axial Power Shape Operating Space Envelope
REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-31 REACTOR COOLANT SYSTEM PRESSURE (4-INCH BREAK) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-32 CORE MIXTURE HEIGHT (4-INCH BREAK) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-33 CLAD TEMPERATURE TRANSIENT AT PEAK TEMPERATURE ELEVATION (4-INCH BREAK) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-33AMAXIMUM LOCAL ZRO 2 THICKNESS (%) (4-INCH BREAK) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-34 STEAM MASS FLOW RATE OUT TOP OF CORE (4-INCH BREAK) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-34A TOP CORE EXIT VAPOR TEMPERATURE (4-INCH BREAK) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-35 CLAD SURFACE HEAT TRANSFER COEFFICIENT AT PEAK TEMPERATURE ELEVATION (4-INCH BREAK) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-36FLUID TEMPERATURE AT PEAK CLAD TEMPERATURE ELEVATION (4-INCH BREAK) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-36ATOTAL BREAK FLOW & SAFETY INJECTION FLOW (4-INCH BREAK) REV. 22 WOLF CREEK UPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-36B TOTAL REACTOR COOLANT SYSTEM MASS (4-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-37REACTOR COOLANT SYSTEM PRESSURE (2-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-38REACTOR COOLANT SYSTEM PRESSURE (3-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-39REACTOR COOLANT SYSTEM PRESSURE (6-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-39AREACTOR COOLANT SYSTEM PRESSURE (8.75-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-40 CORE MIXTURE HEIGHT (2-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-41 CORE MIXTURE HEIGHT (3-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-42 CORE MIXTURE HEIGHT (6-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-42A CORE MIXTURE HEIGHT (8.75-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-44 CLAD TEMPERATURE TRANSIENT AT PEAK TEMPERATURE ELEVATION (3-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-45 CLAD TEMPERATURE TRANSIENT AT PEAK TEMPERATURE ELEVATION (6-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-45AMAXIMUM LOCAL ZRO 2 THICKNESS (%) (3-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-45BMAXIMUM LOCAL ZRO 2 THICKNESS (%) (6-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-45C TOP CORE EXIT VAPOR TEMPERATURE (2-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-45D TOP CORE EXIT VAPOR TEMPERATURE (3-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-45E TOP CORE EXIT VAPOR TEMPERATURE (6-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-45F TOP CORE EXIT VAPOR TEMPERATURE (8.75-INCH BREAK) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-46PUMPED SAFETY INJECTION FLOW RATE, FAULTED LOOP INJECTS TO RCS PRESSURE (2-6 INCH BREAKS) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-46APUMPED SAFETY INJECTION FLOW RATE, FAULTED LOOP SPILL TO CONTAINMENT PRESSURE (0 PSIG) (2-6 INCH BREAKS) REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-47 HOT ROD AXIAL POWER SHAPE REV.22 WOLF CREEKUPDATED SAFETY ANALYSIS REPORT FIGURE 15.6-48CORE POWER (INCLUDING RESIDUAL FISSION) AFTER REACTOR TRIP (APPLIES TO ALL SMALL BREAKS) WOLF CREEK 15.7 RADIOACTIVE RELEASE FROM A SUBSYSTEM OR COMPONENT
This class of accident can be caused by any of the following events:
- a. Radioactive gas waste system leak or failure - this is
an ANS Condition III event.
- b. Radioactive liquid waste system leak or failure - this
is an ANS Condition III event.
- c. Postulated radioactive release due to liquid tank
failures - this is an ANS Condition IV event.
- d. Fuel handling accident - this is an ANS Condition IV event.
- e. Spent fuel cask drop accidents - this is an ANS
Condition III event.
All of the accidents in this section have been analyzed. It has been
determined that the most severe radiological consequences will result from the
fuel handling accident analyzed in Section 15.7.4.
15.7.1 RADIOACTIVE WASTE GAS DECAY TANK FAILURE
15.7.1.1 Identification of Causes This accident is an infrequent fault. Its consequences are considered in this
section. The accident is defined as an unexpected and uncontrolled release of
radioactive xenon and krypton fission product gases stored in a waste gas decay tank as a consequence of a failure of a single gas tank or associated piping.
15.7.1.2 Sequence of Events and System Operations During a refueling shutdown, the radioactive gases are stripped from the
primary coolant and are stored in the gas decay tanks. After the transfer has
been completed, the tank is assumed to fail. This releases all of the contents of the tank to the radwaste building. Also, since the tanks are isolated from
each other, the only radioactivity released is from the failed tank. For
conservatism, the tank is assumed to fail after 40 years, releasing the peak
inventory expected in the tank.
15.7-1 Rev. 0 WOLF CREEK 15.7.1.3 Core and System Performance
This accident occurs when the reactor is in the shutdown condition. There is
no impact on the core or its system performance.
15.7.1.4 Barrier Performance The only barrier between the released activity and the environment is the
radwaste building. During the course of this accident, the radwaste building
is assumed to remain intact. This means that the only method of release is through the radwaste building ventilation system.
15.7.1.5 Radiological Consequences 15.7.1.5.1 Method of Analysis
15.7.1.5.1.1 Physical Model
Radioactive waste gas decay tanks are used in the design to permit the decay of
radioactive gases as a means of reducing or preventing the release of
radioactive materials to the atmosphere. To evaluate the radiological
consequences of the gaseous waste processing system, it is postulated that
there is an accidental release of the contents of one of the waste gas decay
tanks resulting from a rupture of the tank or from another cause, such as
operator error or valve malfunction. The gaseous waste processing system is so
designed that the tanks are isolated from each other during use, limiting the
quantity of gas released in the event of an accident by preventing the flow of radioactive gas between the tanks.
The principal radioactive components of the waste gas decay tanks are the noble
gases krypton and xenon, the particulate daughters of some of the krypton and
xenon isotopes, and trace quantities of halogens. The maximum amount of waste
gases stored in any one tank occurs after a refueling shutdown, at which time
the waste gas decay tanks store the radioactive gases stripped from the reactor
coolant.
The maximum content of a gas decay tank which is conservatively assumed for the
purpose of computing the noble gas inventory available for release given in
Table 15.7-3. Rupture of the waste gas decay tank is assumed to occur
immediately upon completion of the waste gas transfer, releasing the entire
contents of the tank to the radwaste building. For the purposes of evaluating
the accident, it is assumed that all the activity is released directly to the environment during the 2-hour period immediately following the accident.
15.7-2 Rev. 0 WOLF CREEK 15.7.1.5.1.2 Assumptions and Conditions
The major assumptions and parameters assumed in the analysis are itemized in
Table 15.7-3.
In the evaluation of the waste gas decay tank rupture, the fission product
accumulation and release assumptions of Regulatory Guide 1.24 have been used.
Table 15.7-1 provides a comparison of the assumptions used in the analysis to
those of Regulatory Guide 1.24. The assumptions related to the release of
radioactive gases from the postulated rupture of a waste gas decay tank are:
- a. The reactor has been operating at full core power with 1
percent defective fuel, and a shutdown to cold condition
has been conducted prior to the accident.
- b. All noble gas activity has been removed from the reactor
coolant system and transferred to the gas decay tank
that is assumed to fail.
- c. The maximum content of the waste gas decay tank was
conservatively assumed to calculate the isotopic
activities given in Table 15.7-3 for the accumulated
radioactivity in the gaseous waste processing system
after 40 years' operation and immediately following
plant shutdown. The source term determination does
take into account degassing of the reactor coolant
system at shutdown.
- d. The failure is assumed to occur immediately upon completion of the waste gas transfer, releasing the entire contents of the tank to the radwaste building.
- e. The dose is calculated as if the release were from the
radwaste building at ground level during the 2-hour
period immediately following the accident. No credit
for radioactive decay is taken.
- f. The control building and control room ventilation systems are configured in the normal power generation lineup at the time of the accident and remain in this configuration for the duration of a postulated tank failure event. That is, the control room ventilation isolation signal will not be actuated and consequently, the control room emergency ventilation system is not assumed to operate following the initiation of the accident.
15.7.1.5.1.3 Mathematical Models Used in the Analysis
The mathematical models used in the analysis are described in the following
sections:
- a. The mathematical models used to analyze the activity
released during the course of the accident are described
in Appendix 15A.
- b. The atmospheric dispersion factors used in the analysis
were calculated based on the onsite meteorological
measurement programs described in Section 2.3.
15.7-3 Rev. 26 WOLF CREEK
- c. The thyroid inhalation and total-body immersion doses to
a receptor at the exclusion area boundary or outer
boundary of the low-population zone were analyzed, using
the models described in Appendix 15A, Sections 15A.2.4 and 15A.2.5, respectively.
15.7.1.5.1.4 Identification of Leakage Pathways and Resultant
Leakage Activity
For the purposes of evaluating the radiological consequences due to the
postulated waste gas decay tank rupture, the resultant activity is
conservatively assumed to be released directly to the environment during the 2-
hour period immediately following the occurrence of the accident. This is a
considerably higher release rate than that based on the actual building exhaust ventilation rate. Therefore, the results of the analysis are based on the most conservative pathway available.
15.7.1.5.2 Identification of Uncertainties and Conservatisms
in the Analysis
The uncertainties and conservatisms in the assumptions used to evaluate the
radiological consequences of a waste gas decay tank rupture result from
assumptions made involving the release of the waste gas from the decay tank and
the meteorology present at the site during the course of the accident.
- a. The accumulated activity in the gaseous waste processing
system after 40 years' operation and immediately
following plant shutdown with zero decay assumed to be
in the waste gas decay tank is based on 1 percent failed fuel, which is eight times greater than that assumed under normal operating conditions.
- b. It is assumed that the waste gas decay tank fails
immediately after the transfer of the noble gases from
the reactor coolant to the waste gas decay tank is
complete. These assumptions result in the greatest
amount of noble gas activity available for release to
the environment.
- c. The noble gas activity contained in the ruptured waste
gas decay tank was assumed to be released over a 2-hour
period immediately following the accident. This is a
conservative assumption. If the contents of the tank
were assumed to mix uniformly with the volume of air
within the radwaste building where the decay tanks are
located, then, using the actual building exhaust
ventilation rate, a considerable amount of holdup
time would
15.7-4 Rev. 0 WOLF CREEK be gained. However, no credit for radioactive decay is taken. This reduces the amount of noble gas activity released to the environment
due to natural decay. Also no credit for iodine removal by the non-
safety grade radwaste building HVAC charcoal adsorbers has been taken.
- d. The meteorological conditions which may be present at
the site during the course of the accident are
uncertain. However, it is highly unlikely that
meteorological conditions assumed will be present during
the course of the accident for any extended period of
time. Therefore, the radiological consequences
evaluated, based on the meteorological conditions
assumed, will be conservative. 15.7.1.5.3 Conclusions
15.7.1.5.3.1 Filter Loading
Since the accumulated iodine activity in the waste gas decay tanks is
negligible, filter loading due to a waste gas decay tank rupture does not
establish the necessary design margin for the radwaste building exhaust or the
control room intake filters. Hence, the respective filter loadings were not
evaluated.
15.7.1.5.3.2 Dose to Receptor at the Exclusion Area Boundary
and the Low-Population Zone Outer Boundary
The radiological consequences resulting from the occurrence of a postulated waste gas decay tank rupture have been conservatively analyzed using the RATRAD code, based on assumptions and models described in previous sections. The analysis results show that the radiological consequences of the postulated waste gas decay tank failure do not exceed a small fraction (i.e., 10 percent) of the exposure limits set forth in 10 CFR 100 for offsite doses and well below the dose acceptance criteria specified in SRP Section 6.4, and GDC-19 for the control room, even with no credit taken for the CREVS and its actuation instrumentation. The results are listed in Table 15.7-4 15.7.2 RADIOACTIVE LIQUID WASTE SYSTEM LEAK OR FAILURE
15.7.2.1 Identification of Causes
This is an infrequent fault because, although it is unlikely to happen, the
potential for release of significant amounts of radioactivity is present. The
accident may be caused by an equipment malfunction or tank failure or rupture.
15.7-5 Rev. 26 WOLF CREEK 15.7.2.2 Sequence of Events and System Operation
The radioactive liquid tank is assumed to fail. This releases a maximum of 80
percent of the tank capacity to the equipment compartment.
15.7.2.3 Core and System Performance This accident does not affect the core or the core system performance.
15.7.2.4 Barrier Performance
There are no barriers to the release of radioactivity from the radwaste
building.
15.7.2.5 Radiological Consequences 15.7.2.5.1 Method of Analysis
15.7.2.5.1.1 Physical Model
The liquid radwaste tanks are used as a means of collecting waste to be: 1)
processed through the liquid radwaste system, 2) pumped to the Solid Radwaste
System, or 3) discharged from the plant. To evaluate the radiological
consequences of the liquid waste processing system, it is postulated that there
is an accidental release of the contents of one of the tanks.
Table 11.1-6 provides an inventory and the concentrations of stored
radioactivity in all the liquid tanks. In the analyses, it is assumed that the
liquid contents of the tank are released to the radwaste building and, subsequently, the airborne activity is released to the environment during the 2-hour period immediately following the tank failure.
Two tanks have been analyzed for this accident, and the radiological
consequences for both tanks are provided. The boron recycle holdup tank was
selected because it contained the maximum total inventory, and therefore, the highest whole body exposures. In addition a hypothetical tank containing the maximum possible amount of iodine was analyzed in order to determine the thyroid exposures. Although the primary spent resin tank contains the highest inventory of airborne and soluble iodine, it is considered extremely unlikely that all the iodine activity will become airborne in case the tank fails. The
assumptions, conditions, and mathematical models described in this section are
identical for both tanks, except as stated.
15.7.2.5.1.2 Assumptions and Conditions
The major assumptions and parameters assumed in this analysis are listed below
and in Tables 15.7-5 and 15A-1:
- a. The isotopic inventory of the ruptured tank is taken
from Table 11.1-6, and is based on 1-percent failed
fuel. The isotopic inventory of the ruptured hypothetical tank is also based on 1-percent failed fuel, but was calculated assuming that all of the iodine in the streams entering the liquid radwaste system are concentrated in a hypothetical tank where the only means of depletion is radioactive decay. These input streams are shown on USAR Figure 11.1A-2 sheets 2, 3, and 4.
15.7-6 Rev. 14 WOLF CREEK
- b. The tank failure is assumed to occur when the contents
of the tank are at a maximum.
- c. The doses are calculated as if the release were from the radwaste building at ground level during the 2-hour
period immediately following the accident. No credit is
taken for radioactive decay during holdup in the tank or
in transit to the site boundary.
- d. For the boron recycle holdup tank 100 percent of all noble gas activity in the tank is released while 10 percent of the iodine activity is released as airborne activity. 100 percent of all iodine activity is released from the hypothetical liquid waste tank.
- e. Credit for iodine removal by non-safety grade radwaste
building HVAC charcoal adsorber is not taken.
15.7.2.5.1.3 Mathematical Models Used in the Analysis
- a. The mathematical models used to analyze the activity
released during the course of the accident are described
in Appendix 15A.
- b. The atmospheric dispersion factors used in the analysis
were calculated, based on the onsite meteorological
measurement programs described in Section 2.3, and are
provided in Table 15A-2.
- c. The thyroid inhalation dose and total-body immersion dose to a receptor at the exclusion area boundary or
outer boundary of the low-population zone were analyzed, using the models described in Appendix 15A, Sections
15A.2.4 and 15A.2.5, respectively.
15.7.2.5.1.4 Identification of Leakage Pathways and
Resultant Leakage Activity
For the purposes of evaluating the radiological consequences due to the
postulated liquid radwaste tank rupture, the resultant activity is
conservatively assumed to be released directly to the environment during the 2-
hour period immediately following the occurrence of the accident. This is a
considerably higher release rate than that based on the actual building exhaust
ventilation rate. Therefore, the results of the analysis are based on the most conservative pathway available.
15.7-7 Rev. 14 WOLF CREEK 15.7.2.5.2 Identification of Uncertainties and Conservatisms
in the Analysis
The uncertainties and conservatisms in the assumptions used to evaluate the radiological consequences of the liquid radwaste tank rupture result from
assumptions made involving the release of the radioactivity from the tanks and
the meteorology assumed for the site.
- a. It was assumed that the liquid radwaste tank fails when
the inventory in the tank is a maximum. This assumption
results in the greatest amount of activity available for
release to the environment.
- b. The contents of the ruptured tank are assumed to be released over a 2-hour period immediately following the accident. If the contents of the tank were assumed to
mix uniformly with the volume of air within the radwaste
building where the tanks are located, then, using the
actual building exhaust ventilation rate, a considerable
amount of holdup time would be gained. This reduces the
amount of activity released to the environment due to
the natural decay. Also, no credit for iodine removal
by the radwaste building HVAC charcoal adsorbers is
taken.
- c. The meteorological conditions which may be present at
the site during the course of the accident are
uncertain. However, it is highly unlikely that
meteorological conditions assumed will be present during the course of the accident for any extended period of time.
- d. A tank is assumed to have collected liquid waste based
on operation at 100-percent power with 1 percent failed
fuel for an extended period of time, which is eight
times higher than under normal operating conditions.
15.7.2.5.3 Conclusions
15.7.2.5.3.1 Filter Loadings
The filter loading due to a liquid radwaste tank rupture does not establish the
necessary design margin for the control room intake filters. Thus, the filter
loading was not evaluated.
15.7.2.5.3.2 Doses to Receptor at the Exclusion Area Boundary
and the Low-Population Zone Outer Boundary
The radiological consequences resulting from the occurrence of a postulated
liquid radwaste tank rupture have been conservatively analyzed, using
assumptions and models described in previous sections.
15.7-8 Rev. 0 WOLF CREEK The total-body dose due to immersion and the thyroid dose due to inhalation
have been analyzed for the 0-2-hour dose at the exclusion area boundary and for
the duration of the accident at the low-population zone outer boundary. The results are listed in Table 15.7-6. The resultant dose is a small fraction ( 10 percent) of the exposure limits set forth in 10 CFR 100.
15.7.3 POSTULATED RADIOACTIVE RELEASE DUE TO LIQUID TANK FAILURES
This analysis is presented in Section 2.4.13.3.
15.7.4 FUEL HANDLING ACCIDENTS
The postulated fuel handling accident has been analyzed for two cases: Case 1, a fuel handling accident outside the containment, and Case 2, a fuel handling
accident inside the reactor building.
15.7.4.1 Identification of Causes and Accident Description The accident is defined as the dropping of a spent fuel assembly onto the fuel
storage area floor or refueling pool floor, resulting in the rupture of the
cladding of all the fuel rods in the assembly despite many administrative controls and physical limitations imposed on fuel handling operations. All
refueling operations are conducted in accordance with prescribed procedures.
15.7.4.2 Sequence of Events and Systems Operations The first step in fuel handling is the achievement of plant cold safe shutdown
of the reactor. After a radiation survey of the containment, the disassembly
of the reactor vessel is started. After disassembly is complete, the first fuel handling is started. It is estimated that the earliest time to first fuel
transfer after shutdown is 76 hours. The postulated fuel handling accident is assumed to occur during a core offload
at least 76 hours after shutdown in either the reactor containment building, or in the fuel building subsequent to the transfer of a fuel assembly through the
fuel storage pool transfer gate and prior to placement in a fuel storage pool
storage rack designated location.
15.7.4.3 Core and System Performance
As fuel damage occurs outside the reactor vessel in either the reactor
containment building or fuel building, a postulated fuel handling accident does
not impair the safe operation of the reactor or its associated systems.
15.7.4.4 Barrier Performance A barrier between the released activity and the environment is the reactor
building and the fuel building. Since these buildings are designed seismic
Category I, it is safe to assume that during the course of a fuel handling
15.7-9 Rev. 20 WOLF CREEK accident their integrity is maintained. This means that the pathway for release
of radioactivity for a postulated accident in the fuel building is initially
via auxiliary/fuel building normal exhaust system. After it is isolated on a
high radiation signal, the release pathway is via the ESF emergency filtration system. For a postulated accident in the reactor building, since the
containment personnel airlock (PAL) doors and equipment hatch are allowed to be open during core alterations or movement of irradiated fuels, portion of the gaseous effluent escaping from the refueling water pool in the Reactor
Containment Building could be released to the environment via the open
personnel and equipment hatches. The fuel storage pool and the refueling pool provide minimum decontamination factors of 100 for iodine.
15.7.4.5 Radiological Consequences
15.7.4.5.1 Method of Analysis
15.7.4.5.1.1 Physical Model
The possibility of a fuel-handling accident is remote because of the many
administrative controls and physical limitations imposed on the fuel-handling
operations (refer to Section 9.1.4). All refueling operations are conducted in
accordance with prescribed procedures.
When transferring irradiated fuel from the core to the fuel storage pool for
storage, the reactor cavity and refueling pool are filled with borated water at
a boron concentration equal to that in the fuel storage pool, which ensures
subcritical conditions in the core even if all rod cluster control (RCC) assemblies were withdrawn. After the reactor head and rod cluster control drive shafts are removed, fuel assemblies are lifted from the core, transferred
vertically to the refueling pool, placed horizontally in a conveyor car and
pulled through the transfer tube and canal, upended and transferred through the
fuel storage pool transfer gate, then lowered into steel racks for storage in
the fuel storage pool in a pattern which precludes any possibility of a
criticality accident.
Fuel-handling manipulators and hoists are designed so that the fuel cannot be
raised above a position that provides an adequate water shield depth for
radiation protection of operating personnel.
The containment, fuel building, refueling cavity, refueling pool, and fuel
storage pool are designed to seismic Category I requirements, which prevent the
structures themselves from failing in the event of a safe shutdown earthquake. The spent fuel storage racks are also designed to prevent any credible external missile from reaching the stored irradiated fuel. The fuel-handling
manipulators, cranes, trollies, bridges, and associated equipment above the
water cavities through which the fuel assemblies move are
15.7-10 Rev. 21 WOLF CREEK designed to prevent this equipment from generating missiles and damaging the
fuel. The construction of the fuel assemblies precludes damage to the fuel
should portable or hand tools drop on an assembly.
The only time the postulated fuel-handling accident could occur is during the
transfer of a fuel assembly from the core to its storage position in the fuel
storage pool. The facility is designed so that heavy objects, such as the
spent fuel shipping cask, cannot be carried over or tipped over onto the
irradiated fuel stored in the fuel storage pool. Only one fuel assembly is
handled at a time by the refueling machine, transfer system, or spent fuel pool
bridge crane. Movement of equipment handling the fuel is kept at low speeds
while exercising caution that the fuel assembly does not strike another object
or structure during transfer from the core to its storage position. In the
unlikely event that an assembly becomes stuck in the transfer tube, natural convection will maintain adequate cooling.
- a. Reactor Building Accident
During fuel-handling operations, the containment is kept
in an isolatable condition, with all penetrations to the
outside atmosphere either closed or capable of being
closed on an alarm signal from one of the redundant
radiation monitors, indicating that radioactivity is
above the prescribed limits.
In addition to the area radiation monitors in the
containment, portable monitors capable of sounding
audible alarms are to be located in the fuel-handling
area. Should a fuel assembly be dropped and release activity above a prescribed level, the radiation monitors would sound an audible alarm, the containment would be isolated, and personnel would be evacuated.
During movement of irradiated fuel and core alterations, one door in the emergency air lock must be closed. The other emergency air lock door may be open provided it is capable of being closed. The equipment hatch may be open provided it is capable of being closed, and penetration flow paths providing direct access may be unisolated under administrative controls. Administrative controls are imposed for the closure of a personnel air lock door, closure of the equipment hatch, and to isolate open penetration flow paths in the event of a fuel handling accident.
- b. Fuel Building Accident
In the fuel building, a fuel assembly could be dropped
in the transfer canal or in the fuel storage pool.
15.7-11 Rev. 21 WOLF CREEK In addition to the area radiation monitor located on the bridge over the fuel storage pool, portable radiation monitors capable of emitting audible alarms are located in this area during fuel-handling operations. The doors in the fuel building are closed to maintain controlled leakage characteristics in the fuel storage pool region during operations involving irradiated fuel. Should a fuel assembly be dropped in the canal or in the pool and release radioactivity above a prescribed level, the radiation monitors sound an alarm, If one of the redundant discharge vent radiation monitors indicates that the radioactivity in the vent discharge is greater than the prescribed levels, an alarm sounds and the auxiliary/fuel building normal exhaust is switched to the ESF Emergency Exhaust system to allow the spent fuel pool ventilation to exhaust through the ESF charcoal filters to remove most of the halogens prior to discharging to the atmosphere via the unit vent. The supply ventilation system servicing the fuel storage pool area is automatically shut down, thus ensuring controlled leakage to the atmosphere through charcoal adsorbers (refer to Section 9.4). The probability of a fuel-handling accident is very low because of the safety
features, administrative controls, and design characteristics of the facility, as previously mentioned.
15.7.4.5.1.2 Assumptions and Conditions
The major assumptions and parameters assumed in the analysis are itemized in
Tables 15.7-7 and 15A-1.
In the evaluation of the fuel-handling accident, all the fission product
release assumptions of Regulatory Guide 1.25 have been followed. Table 15.7-2
provides a comparison of the design to the requirements of Regulatory Guide
1.25. The following assumptions, related to the release of fission product gases from the damaged fuel assembly, were used in the analyses:
- a. The dropped fuel assembly is assumed to be the assembly
containing the peak fission product inventory. All the
fuel rods contained in the dropped assembly are assumed
to be damaged. In addition, for the analyses for the
accident in the reactor building the dropped assembly is
assumed to damage 20 percent of the rods of an
additional assembly.
- b. The assembly fission product inventories are based on a
radial peaking factor of 1.65.
15.7-12 Rev. 19 WOLF CREEK
- c. The accident occurs 76 hours after shutdown, which is the earliest time fuel-handling operations can begin.
Radioactive decay of the fission product inventories was taken into account during this time period.
- d. Only that fraction of the fission products which migrates from the fuel matrix to the gap and plenum regions during normal operation was assumed to be available for immediate release to the water following clad damage.
- e. The gap activity released to the fuel pool from the damaged fuel rods consists of 10 percent of the total
noble gases other than Kr-85, 30 percent of the Kr-85, and 10 percent of the total radioactive iodine other than
I-131, 12 percent of the I-131, contained in the fuel rods at the time of the accident.
- f. The pool decontamination factor is 1.0 for noble gases.
- g. The effective pool decontamination factor is 100 for iodine assuming at least 23 feet of water above the top of
the damaged fuel assemblies is maintained in the pool. In
the case of a single bundle dropped and lying horizontally
on top of the spent fuel racks, however, there may be < 23
ft of water above the top of the fuel bundle and the surface, indicated by the width of the bundle. To offset this small
nonconservatism, the analysis assumes that all fuel rods fail, although analysis shows that only the first few rows fail
from a hypothetical maximum drop.
- h. The iodine above the fuel pool is assumed to be composed of 75 percent inorganic and 25 percent organic species.
- i. The activity which escapes from the pool is assumed to be available for release to the environment in a time period of 2 hours.
- j. No credit for decay or depletion during transit to the site boundary and outer boundary of the low-population zone is assumed.
- k. No credit is taken for mixing or holdup in the fuel building atmosphere. The filter efficiency for the ESF
emergency filtration system is assumed to be 82.5 percent
which is based on the assumption of the failure of the
humidity control system.
- l. The fuel building is switched from the auxiliary/fuel building normal exhaust system to the ESF emergency exhaust system within one
minute from the time the activity reaches the exhaust duct. The
activity released before completion of the switchover is assumed to
be discharged directly to the environment with no credit for
filtration or dilution.
15.7-13 Rev. 20 WOLF CREEK
- m. For the inside the reactor building case, the containment personnel airlock doors and equipment hatch are assumed to be open at the time of the accident. For added conservatism, the gaseous effluent escaping from the refueling water pool in the Reactor Containment
Building is assumed to be released immediately to the environment
through the open personnel and equipment hatch and the adjacent Auxiliary Building without mixing in the surrounding atmosphere.
The activity releases continue until the containment personnel
airlock doors and equipment hatch are closed (assumed to be accomplished within two hours). The Auxiliary Building atmosphere
is normally exhausted through filter absorbers designed to remove
iodine. However, no credit is taken for iodine removal by the
atmosphere filtration system filters. It is also assumed that no
containment coolers or hydrogen mixing fans are operating and 99.99% of the activity escaping from the pool to the containment building
is released to the environment over a two-hour period following the
accident.
15.7.4.5.1.3 Mathematical Models Used in the Analysis
Mathematical models used in the analysis are described in the following
sections:
- a. The mathematical models used to analyze the activity released during the course of the accident are described
in Appendix 15A, Section 15A.2.
- b. The atmospheric dispersion factors are calculated, based
on the onsite meteorological measurements programs
described in Section 2.3 and are provided in Table
15A-2.
- c. The thyroid inhalation and total-body immersion doses to
a receptor located at the exclusion area boundary and
outer boundary of the low population zone are described
in Appendix 15A, Sections 15A.2.4 and 15A.2.5, respectively.
15.7.4.5.1.4 Identification of Leakage Pathways and Resultant Leakage Activity
For evaluating the radiological consequences due to the postulated fuel-
handling accident in the fuel building and reactor building, the resultant
activity is conservatively assumed to be released to the environment during the
0-2-hour period immediately following the occurrence of the accident. This is
a considerably higher release rate than that based on the actual ventilation
rate. Therefore, the results of the analysis are based on the most
conservative pathway available.
15.7.4.5.2 Identification of Uncertainties and Conservatisms
in Analysis
The uncertainties and conservatisms in the assumptions used to evaluate the
radiological consequences of a fuel-handling accident result from assumptions
made involving the amount of fission
15.7-14 Rev. 21 WOLF CREEK product gases available for release to the environment and the meteorology
present at the site during the course of the accident. The most significant of
these assumptions are:
- a. It is assumed in the analysis that all the fuel rods in the dropped assembly are damaged. This is a highly conservative assumption since, transferring fuel under strict fuel handling procedures, only under the worst possible circumstances could the dropping of a spent fuel assembly result in damage to all the fuel rods contained in the assembly.
- b. The fission product gap inventory in a fuel assembly is dependent on the power rating of the assembly and the temperature of the fuel. It has been conservatively assumed that the core has been operating at 100 percent for the entire burnup period. The gap activities are listed in Table 15A-3.
- c. Iodine removal from the released fission product gas takes place as the gas rises to the pool surface through the body of liquid in the fuel storage and refueling water pools. The extent of iodine removal is determined by mass
transfer from the gas phase to the surrounding liquid and is controlled by the bubble diameter and contact time of the bubble in the solution. The values used in the analysis result in a release of activity approximately a factor of 5 greater than anticipated.
Radioactive material from the refueling water pool in the reactor containment building is assumed to be released directly to the environment through the open personnel and equipment hatch and the adjacent auxiliary building, without mixing in the surrounding atmosphere. Radioactive material is assumed to be released from the auxiliary building or from the fuel building over a two-hour time period.
- d. The ESF emergency filtration system charcoal filters are known to operate with at least a 99-percent efficiency.
This means a further reduction in the iodine concentrations and thus a reduction in the thyroid doses at the exclusion area boundary and the outer boundary of the low-population zone for the fuel handling accident in the fuel building.
- e. The containment purge exhaust system has charcoal adsorber units which filter any containment purge release. However, no credit has been taken for its capability (90-percent efficiency, minimum) since these units are not specifically designed to seismic Category I criteria. It is expected that for any event which would produce a catastrophic failure of the charcoal adsorber unit to the extent that its filtering capability would be negated
15.7-15 Rev. 21 WOLF CREEK would also result in the purge exhaust fan becoming
inoperable. Therefore, failure within the purge exhaust
system would terminate any high volume release from the
containment. In fact, the purge exhaust fan is considerably more likely to be inoperable following any
postulated event than the failure of a passive charcoal
adsorber unit. Thus, although no credit in the analysis
has been given for the normal purge exhaust filters, any
release prior to containment isolation would be filtered.
- f. There is also conservatism in the time to first fuel
transfer. Despite the fact that fuel could be
transferred at 76 hours, it is probable that fuel handling will begin sometime later.
- g. The meteorological conditions which may be present at the
site during the course of the accident are uncertain.
However, it is highly unlikely that meteorological conditions assumed will be present during the course of
the accident for any extended period of time. Therefore, the radiological consequences evaluated, based on the
meteorological conditions assumed, are conservative.
15.7.4.5.2.1 Filter Loadings
The ESF filtration systems which function to limit the consequences of a fuel-
handling accident in the fuel building are the ESF emergency filtration system
and the control room filtration system. The activity loadings on the control room charcoal adsorbers as a function of
time have been evaluated for the loss-of-coolant accident, Section 15.6.5.
Since these filters are capable of accommodating the design basis LOCA fission
product iodine loadings, more than adequate design margin is available with
respect to postulated fuel-handling accident releases.
The activity loadings on the ESF filtration system charcoal adsorbers have been
evaluated in accordance with Regulatory Guide 1.52, which limits the maximum
loading to 2.5 mg of iodine per gram of activated charcoal.
15.7.4.5.2.2 Doses to Receptor at the Exclusion Area Boundary
and Low-Population Zone Outer Boundary
The potential radiological consequences resulting from the occurrence of a postulated fuel-handling accident occurring in the fuel building and in the reactor building have been conservatively
15.7-16 Rev. 20 WOLF CREEK analyzed, using assumptions and models described in previous sections. The
total-body dose due to immersion from direct radiation and the thyroid dose due
to inhalation have been analyzed for the 0-2-hour dose at the exclusion area
boundary and for the duration of the accident (0 to 2 hours) at the low-population zone outer boundary. The results are listed in Table 15.7-8. The
resultant doses are well within the guideline values of 10 CFR 100.
15.7.5 SPENT FUEL CASK DROP ACCIDENTS
The design of the spent fuel cask handling equipment is such that no cask could
be dropped more than the equivalent of 30 feet in the air. Therefore, no cask
rupture will occur and thus no radioactivity will be released. Refer to
Section 9.1.4 for a description of the spent fuel shipping procedures.
15.7-17 Rev. 0 WOLF CREEK TABLE 15.7-1 DESIGN COMPARISON TO THE REGULATORY POSITIONS OF REGULATORY GUIDE 1.24 "ASSUMPTIONS USED FOR EVALUATING THE POTENTIAL CONSEQUENCES OF A PRESSURIZED WATER REACTOR RADIOACTIVE GAS STORAGE TANK FAILURE" REVISION 0, DATED MARCH 23, 1972 Regulatory Guide 1.24 Position Design
- 1. The assumptions related to the release of radioactive gases
from the postulated failure of a gaseous waste storage tank are:
- a. The reactor has been operating 1.a Complies.
at full power with one percent defective fuel and a shutdown
to cold condition has been conducted near the end of an equilibrium core cycle. As soon as possible after shut-
down, all noble gases have
been removed from the primary
cooling system and transferred
to the gas decay tank that is assumed to fail.
- b. The maximum content of the 1.b Complies.
decay tank assumed to fail
should be used for the pur-
pose of computing the noble
gas inventory in the tank.
Radiological decay may be taken
into account in the computation
only for the minimum time period
required to transfer the gases
from the primary system to the
decay tank.
- c. The failure is assumed to occur 1.c Complies.
immediately upon completion of the waste gas transfer, releasing the entire contents of the tank to the building. The assump-
tion of the release of the noble gas inventory from only a single tank is based
on the premise that all gas
decay tanks will be isolated
from each other whenever
they are in use. Rev. 0 WOLF CREEK TABLE 15.7-1 (S heet 2) Regulatory Guide 1.24 Position Design
- d. All of the noble gases are 1.d Complies.
assumed to leak out of the
building at ground level
over a 2-hour time period.
- 2. The atmospheric diffusion assump- 2.
S hort-term atmospheric tions for ground level releases are: dispersion factors corresponding to a
- a. The basic equation for at- ground level release and mospheric diffusion from a accident conditions were ground level point source calculated based on on-
is: site meteorological mea-
surement programs described in S ection 2.3. The disper- /Q = 1 sion factors are in compli- u y z ance with the methodology described in Regulatory Guide Where: 1.145 and represent the worst of the 5 percent overall site = the short term average meteorology and the 0.5 centerline value of percent worst sector the ground level con- meteorology. centration (curies/m
- 3) Q = amount of material released (curies/sec) u = windspeed (meters/sec) y = the horizontal standard deviation of the plume (meters) [
S ee Figure V-1, page 48, Nuclear
S afety, June 1961, Volume 2, Number 4, "Use of Routine Meteorological Observations for Esti-mating Atmospheric
Dispersion," F. A.
Gifford, Jr.] Rev.1 WOLF CREEK TABLE 15.7-1 (S heet 3) Regulatory Guide 1.24 Position Design z = the vertical standard deviation of the plume (meters) [ S ee Figure V-2, page 48, Nuclear S afety, June 1961, Volume 2, Number 4, "Use of Routine
Meteorological
Observations for Esti-
mating Atmospheric
Dispersion," F. A.
Gifford, Jr.]
- b. For ground level releases, atmospheric diffusion factors 1 used in evaluating the radio-logical consequences of the
accident addressed in this guide
are based on the following
assumptions:
(1) windspeed of 1 meter/sec;
(2) uniform wind direction
(3) Pasquill diffusion cat-
egory F.
- c. Figure 1 is a plot of atmospheric diffusion factors
(/Q) versus distance derived by use of the equation for a ground level release given in regulatory position 2.a. above
under the meteorological
conditions given in regulatory
position 2.b. above.
- 3. The following assumptions and 3. Dose factors given in Regula-equations may be used to obtain tory Guide 1.109 for noble
conservative approximations of gases and iodine thyroid dose
external whole body dose from factors; iodine whole body
radioactive clouds: dose factors were calculated
with 5 cm body tissued atten-
- a. External whole body doses are uation; see Table 15A-4.
calculated using "Infinite
Cloud" assumptions, i.e., the dimensions of the cloud are assumed to be large compared to
the distances that the gamma
rays and beta particles travel. Rev. 1 WOLF CREEK TABLE 15.7-1 (S heet 4) Regulatory Guide 1.24 Position Design The dose at any distance from the reactor is calculated based
on the maximum ground level concentration at that distance. For an infinite uniform cloud containing curies of beta
radioactivity per cubic meter, the beta dose rate in air at the cloud center is: 2 D'oo = 0.457 E _ Where: D'oo = beta dose rate from an infinite cloud (rad/sec) E_ = average beta energy per disintegration (Mev/dis) = concentration of beta or gamma emitting iso-
tope in the cloud (curie/m
- 3) Because of the limited range of beta particles in tissue, the
surface body dose rate from
beta emitters in the infinite
cloud can be approximated as
being one-half this amount or: D'oo = 0.23 E_ For gamma emitting material the
dose rate in air at the cloud
center is: D'oo = 0.507E_ Rev. 1 WOLF CREEK TABLE 15.7-1 (S heet 5) Regulatory Guide 1.24 Position Design Where: D'oo = gamma dose rate from an infinite cloud (rad/sec) E _ = average gamma energy per disintegration (Mev/dis) However, because of the pres-ence of the ground, the receptor is assumed to be exposed to only one-half of the
cloud (semi-infinite) and the
equation becomes: D' = 0.25 E _ Thus, the total beta or gamma
dose to an individual located
at the center of the cloud path
may be approximated as: D oo = 0.23 E _ or D oo = 0.25 E _ Where is the concentration
time integral for the cloud
(curie sec/m3).
- b. The beta and gamma energies emitted per disintegration, as given in Table of Isotopes,3
are averaged and used according
to the methods described in
ICRP Publication 2. Rev. 1 WOLF CREEK TABLE 15.7-1 (S heet 6) Regulatory Guide 1.24 Position Design 1 These diffusion factors should be used until adequate site meteorological data are obtained. In some cases, available information on such site conditions as meteorology, topography and geographical location may dictate
the use of more restrictive parameters
to insure a conservative estimate of
potential offsite exposures. 2 Meteorology and Atomic Energy - 1968, Chapter 7. 3 C. M. Lederer, J. M. Hollander, and I. Perlman, Table of Isotopes, S ixth Edition (New York: John Wiley and S ons, Inc., 1967). Rev. 0 WOLF CREEK TABLE 15.7-2 DESIGN COMPARISON TO THE REGULATORY POSITIONS OF REGULATORY GUIDE 1.25 "ASSUMPTIONS USED FOR EVALUATING THE POTENTIAL RADIOLOGICAL CONSEQUENCES OF A FUEL HANDLING ACCIDENT IN THE FUEL HANDLING AND STORAGE FACILITY FOR BOILING AND PRESSURIZED WATER REACTORS" REVISION 0, DATED MARCH 23, 1972 Regulatory Guide 1.25 Position Case 1 (in Fuel Building) Case 2 (in Reactor Building)1. The assumptions 1 related to the release of radioactive material from the fuel and fuel storage facility as a result of a fuel handling accident are: a. The accident occurs at a time after shutdown identified in the technical specifications as the earliest time fuel handling operations may begin. Radioactive decay of the fission product inventory during the interval between shutdown and commencement of fuel handling operations is taken into consideration. Complies, except the time after shutdown is
identified in S ection 9.1.4.2.3. Accident
occurs 76 hours after shutdown.Complies, except the time after shutdown is
identified in S ection 9.1.4.2.3. Accident occurs
76 hours after shutdown. b. The maximum fuel rod pressuri-zation 2 is 1200 psig. Complies. Complies. c. The minimum water depth 2 between the top of the damaged fuel rods and the fuel pool surface is 23 feet. Complies. Water depth is greater than
23 feet. Complies. Water
depth is greater
than 23 feet. Rev. 20 WOLF CREEK TABLE 15.7-2 (S heet 2) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
- d. All of the gap activity in the Complies. Complies.
damaged rods is released and
consists of 10% of the total
noble gases other than Kr-85, 30% of the Kr-85, and 10% of the
total radioactive iodine in the
rods at the time of the accident.
For the purpose of sizing filters
for the fuel handling accident
addressed in this guide, 30% of
the I-127 and I-129 inventory
is assumed to be released from
the damaged rods.
- e. The values assumed for individual Complies. A peaking Complies. A peaking fission product inventories are factor of 1.65 is factor of 1.65 is used.
calculated assuming full power used.
operation at the end of core life
immediately preceding shutdown
and such calculation should in-
clude an appropriate radial peaking factor. The minimum acceptable radial peaking factors are 1.5 for
BWR's and 1.65 for PWR' S. f. The iodine gap inventory is com- Complies. Complies. posed of inorganic species (99.75%) and organic species (.25%).
- g. The pool decontamination factors Complies. Complies.
for the inorganic and organic
species are 133 and 1, respec-
tively, giving an overall effective
decontamination factor of 100
(i.e., 99% of the total iodine Rev. 0 WOLF CREEK TABLE 15.7-2 (S heet 3) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building) released from the damaged rods is retained by the pool water). This
difference in decontamination factors for inorganic and organic iodine species results in the iodine above the fuel pool being composed of 75% inorganic and 25% organic species.
- h. The retention of noble gases in Complies. A decon- Complies. A decon-the pool is negligible (i.e., tamination factor of 1 tamination factor
decontamination factor of 1). is used. of 1 is used.
- i. The radioactive material that Complies. A 0-2 hour The containment shutdown
escapes from the pool to the release from the pool purge lines are automatically
building is released from the to the building to the isolated upon detection of building 3 over a 2-hour time environment is assumed. high radioactivity in the period. containment. It is con-servatively assumed
that isolation does not
occur until 25 seconds
after the release. The containment minipurge lines are assumed to automatically isolate in less than 25 seconds after the release. Therefore, the greatest portion of the activity
is contained in the
reactor building
following the event.
- j. If it can be shown that the build- Not applicable; No credit is taken ing atmosphere is exhausted through complies with Regula- for the normal purge adsorbers designed to remove iodine, tory Guide 1.52 as de- filters.
the removal efficiency is 90% for scribed in Table 9.4-2. inorganic species and 70% for organic species. 4 Rev. 19 WOLF CREEK TABLE 15.7-2 (S heet 4) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
- k. The effluent from the filter Complies. Complies.
system passes directly to the
emergency exhaust system without
mixing5 in the surrounding building
atmosphere and is then released
(as an elevated plume for those facilities with stacks 6).2. The assumptions for atmospheric dif-S hort-term atmospheric dispersion fusion are: factors corresponding to ground level release and accident conditions were
- a. Ground Level Releases based on meteorological measurement
programs described in S ection 2.3.
(1) The basic equation for atmos- The dispersion factors are in com-
pheric diffusion from a pliance with the methodology described
ground level point source is: in Regulatory Guide 1.145 and represent the worst of the 5 percent overall site /Q = 1 meteorology and the 0.5 percent worst u y z sector meteorology. Where: = the short term average centerline value of the
ground level concen-tration (curies/m
- 3) Q = amount of material re-leased (curies/sec) u = windspeed (meters/sec)
= the horizontal standard y deviation of the plume (meters) [
S ee Figure V-1, Rev. 1 WOLF CREEK TABLE 15.7-2 (S heet 5) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
Page 48, Nuclear S afety, June 1961, Volume 2, Num-
ber 4, "Use of Routine
Meteorological Obser-
vations for Estimating
Atmospheric Dispersion," F. A. Gifford, Jr.] z = the vertical standard de-viation of the plume (meters) [ S ee Figure V-2, Page 48, Nuclear S afety, June 1961, Volume 2, Number 4, "Use of Routine
Meteorological Observa-
tions for Estimating
Atmospheric Dispersion," F. A. Gifford, Jr.]
(2) For ground level releases, at-mospheric diffusion factors 7 used in evaluating the radio-logical consequences of the accident addressed in this guide
are based on the following
assumptions:
(a) windspeed of 1 meter/sec;
(b) uniform wind direction; (c) Pasquill diffusion cate-gory F.
(3) Figure 1 is a plot of atmos-pheric diffusion factors (/Q) versus distance derived by use Rev. 1 WOLF CREEK TABLE 15.7-2 (S heet 6) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building) of the equation for a ground
level release given in
regulatory position 2.a.(1)
and under the meteorological conditions given in regulatory
position 2.a.(2).
(4) Atmospheric diffusion factors for ground level releases may
be reduced by a factor ranging
from one to a maximum of three
(see Figure 2) for additional
dispersion produced by the
turbulent wake of the reactor
building. The volumetric
building wake correction as
defined in S ubdivision 3-3.5.2 of Meteorology and Atomic
Energy-1968, is used with a
shape factor of 1/2 and the minimum cross-sectional area of the reactor building only.
- b. Elevated Releases
(1) The basic equation for atmos- Not applicable. Not applicable.
pheric diffusion from an ele- Ground level releases Ground level releases
vated release is: were assumed. were assumed. /Q =e-h 2/2 2 z u y z Rev. 1 WOLF CREEK TABLE 15.7-2 (S heet 7) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
Where: = the short term average centerline value of the
ground level concen-tration (curies/m
- 3) Q = amount of material re-leased (curies/sec) u = windspeed (meters/sec) y = the horizontal standard deviation of the plume (meters) [
S ee Figure V-1, Page 48, Nuclear S afety, June 1961, Volume 2, Number 4, "Use of Routine
Meteorological Observa-
tions for Estimating
Atmospheric Dispersion," F. A. Gifford, Jr.] z = the vertical standard deviation of the plume (meters) [ S ee Figure V-2, Page 48, Nuclear S afety, June 1961, Volume 2, Number 4, "Use of Routine Meteorological Observa-
tions for Estimating
Atmospheric Dispersion," F. A. Gifford, Jr.] h = effective height of release (meters) Rev. 1 WOLF CREEK TABLE 15.7-2 (S heet 8) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
(2) For elevated releases, atmos-pheric diffusion factors 7 used in evaluating the radiological consequences of the accident
addressed in this guide are
based on the following assump-
tions:
(a) windspeed of 1 meter/sec;
(b) uniform wind direction;
(c) envelope of Pasquill dif-
fusion categories for
various release heights; (d) a fumigation condition exists at the time of the accident. 8 (3) Figure 3 is a plot of atmos-pheric diffusion factors versus
distance for an elevated
release assuming no fumigation, and Figure 4 is for an elevated release with fumigation.
(4) Elevated releases are consid-ered to be at a height equal to
no more than the actual stack
height. Certain site condi-
tions may exist, such as
surrounding elevated topography
or nearby structures, which
will have the effect of reduc-
ing the effective stack
height. The degree of stack
height reduction will be eval-
uated on an individual case Rev. 0 WOLF CREEK TABLE 15.7-2 (S heet 9) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
- 3. The following assumptions and equa-
tions may be used to obtain con-
servative approximations of thyroid
dose from the inhalation of radio-iodine and external whole body dose
from radioactive clouds:
- a. The assumptions relative to in- Complies.
S ee Appendix Complies. S ee Appendix halation thyroid dose approxi- 15A, S ection 15A.2.4. 15A, S ection 15A.2.4. mations are:
(1) The receptor is located at a point on or beyond the site
boundary where the maximum
ground level concentration is
expected to occur.
(2) No correction is made for depletion of the effluent plume of radioiodine due to
deposition on the ground, or for the radiological decay or
radioiodine in transit.
(3) Inhalation thyroid doses may be approximated by use of the
following equation: D = F q IFPBR(/Q)(DF p)(DF f) Where: D = thyroid dose (rads) Rev. 1 WOLF CREEK TABLE 15.7-2 (S heet 10) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
F g = fraction of fuel rod iodine inventory in fuel rod void space (0.1) I = core iodine inventory at time of accident (curies) F = fraction of core damaged so as to release void
space iodine P = fuel peaking factor
B = Breathing rate = 3.47 x 10 -4 cubic meters per second (i.e., 10 cubic meters per 8 hour work
day as recommended by the ICRP) DF p = effective iodine decon-tamination factor for pool water DF f = effective iodine decon-tamination factor for filters (if present) /Q = atmospheric diffusion factor at receptor location (sec/m 3)Rev. 0 WOLF CREEK TABLE 15.7-2 (S heet 11) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
R = adult thyroid dose con-
version factor for the
iodine isotope of in-
terest (rads per curie).
Dose conversion factors
for Iodine 131-135 are listed in Table 1. 9 These values were derived from "standard man" parameters
recommended in ICRP Publication 2. 10 TABLE 1 Adult Inhalation Thyroid Table 1; the thyroid Table 1; the thyroid Dose Conversion Factors dose conversion factors dose conversion factors
given in Regulatory given in Regulatory Iodine Conversion Factor (R) Guide 1.109 are used. Guide 1.109 are used. Isotope (Rads/curie inhaled) 131 1.48 x 10 6 132 5.35 x 10 4 133 4.0 x 10 5 134 2.5 x 10 4 135 1.24 x 10 5 b. The assumptions relative to Complies. S ee Appendix Complies. S ee Appendix external whole body dose approx- 15A, S ection 15A.2.5. 15A, S ection 15A.2.5. imations are:
(1) The receptor is located at a point on or beyond the site boundary where the maximum ground level concentration is
expected to occur. Rev. 0 WOLF CREEK TABLE 15.7-2 (S heet 12) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
(2) External whole body doses are (2) The whole-body dose factors for
calculated using "Infinite gammas given in Regulatory Guide
Cloud" assumptions, i.e., the 1.109 are used; for iodines, the
dimensions of the cloud are whole-body dose factors for gammas assumed to be large compared with credit for 5 cm body tissue
to the distances that the attenuation are used. S ee Table gamma rays and beta particles 15A-4 for dose conversion factors. travel. The dose at any distance
from the reactor is calculated
based on the maximum ground
level concentration at that
distance. For an infinite uniform cloud containing curies of beta
radioactivity per cubic meter, the beta dose rate in air at the cloud center is: 11 - D'oo = 0.457 E _ Where: D'oo= beta dose rate from an infinite cloud (rad/sec) E _ = average beta energy per disintegration (Mev/dis) = concentration of beta or gamma emitting isotope in the cloud (curie/m 3)Rev. 1 WOLF CREEK TABLE 15.7-2 (S heet 13) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
Because of the limited range
of beta particles in tissue, the surface body dose rate
from beta emitters in the infinite cloud can be approx-
imated as being one-half this
amount or: D'oo = 0.23 E_ For gamma emitting material the dose rate in tissue at the cloud center is: D'oo = 0.507 E _ Where: D'oo= gamma dose rate from an infinite cloud (rad/sec) E _ = average gamma energy per disintegration (Mev/dis) However, because of the pres-ence of the ground, the receptor is assumed to be
exposed to only one-half of
the cloud (semi-infinite) and
the equation becomes: D' = 0.25 E_ Rev. 1 WOLF CREEK TABLE 15.7-2 (S heet 14) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
Thus, the total beta or gamma
dose to an individual located
at the center of the cloud
path may be approximated as: Doo = 0.23 E_ orDoo = 0.23 E_ Where is the concentration time integral for the cloud (curie sec/m 3). (3) The beta and gamma energies emitted per disintegration, as given in Table of Isotopes, 12 are averaged and used accord-ing to the methods described
in ICRP Publication 2. Notes: 1 The assumptions given are valid only for oxide fuels of the types currently in use and in cases where the following con-
ditions are not exceeded:
- a. Peak linear power density of 20.5 kW/ft for the highest power assem-
bly discharged.
- b. Maximum center-line operating fuel temperature less than 4500 F for
this assembly. Rev. 1 WOLF CREEK TABLE 15.7-2 (S heet 15) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building)
- c. Average burnup for the peak assem-
bly of 25,000 MWD/ton or less (this
corresponds to a peak local burnup
of about 45,000 MWD/ton). 2 For release pressures greater than 1200 psig and water depths less than 23
feet, the iodine decontamination factors
will be less than those assumed in this guide and must be calculated on an indi-
vidual case basis using assumptions com-
parable in conservatism to those of this guide.3 The effectiveness of features pro-vided to reduce the amount of radioactive
material available for release to the
environment will be evaluated on an in-dividual case basis. 4 These efficiencies are based upon a 2-inch charcoal bed depth with 1/4 second residence time. Efficiencies may be dif-
ferent for other systems and must be cal-
culated on an individual case basis. 5 Credit for mixing will be allowed in some cases; the amount of credit will be
evaluated on an individual case basis. 6 Credit for an elevated release will be given only if the point of release is (a)
more than two and one-half times the height
of any structure close enough to affect the Rev. 0 WOLF CREEK TABLE 15.7-2 (S heet 16) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building) dispersion of the plume or (b) located far
enough from any structure which could affect
the dispersion of the plume. For those
plants without stacks the atmospheric diffu-sion factors assuming ground level release
given in regulatory position 2.b should be
used.7 These diffusion factors should be used until adequate site meteorological data are obtained. In some cases, available informa-
tion on such site conditions as meteorology, topography and geographical location may
dictate the use of more restrictive para-
meters to ensure a conservative estimate of
potential offsite exposures. 8 For sites located more than 2 miles from large bodies of water such as oceans or
one of the Greak Lakes, a fumigation condi-tion is assumed to exist at the time of the accident and continue for 1/2 hour. For
sites located less than 2 miles from large
bodies of water a fumigation condition is
assumed to exist at the time of the acci-
dent and continue for the duration of the
release (2 hours). Rev. 0 WOLF CREEK TABLE 15.7-2 (S heet 17) Regulatory Guide 1.25 Case 1 Case 2 Position (in Fuel Building)
(in Reactor Building) 9 Dose conversion factors taken from "Calculation of Distance Factors for Power and Test Reactor S ites," TID-14844, J. J.
DiNunno, R. E. Baker, F. D. Anderson, and R. L. Waterfield (1962). 10 Recommendations of the International Commission on Radiological Protection, "Report of Committee II on Permissible Dose
for Internal Radiation (1959)," ICRP Publication 2, (New York: Permagon Press, 1960).11 Meteorology and Atomic Energy-1968, Chapter 7. 12 C. M. Lederer, J. M. Hollander, and I. Perlman, Table of Isotopes, S ixth Edition (New York: John Wiley and S ons, Inc. 1967). Rev. 0 TABLE 15.7-3 PARAMETERS USED IN EVALUATING THE RADIOLOGICAL CONSEQUENCES OF A WASTE GAS DECAY TANK RUPTUREI.Source Dataa.Core power level, MWt3,565b.Failed fuel, percent1II.Atmospheric Dispersion FactorsSee Table 15A-2III.Activity Release DataIsotope0-2 hr (Ci)I-1314.02E-2I-1320.00I-1333.50E-2I-1340.00I-1351.39E-2Xe-131m9.05E+2Xe-133m1.14E+3Xe-1337.09E+4Xe-135m5.99E+1Xe-1351.15E+3Xe-1373.42E-1Xe-1384.40Kr-83m2.26E+1Kr-85m1.85E+2Kr-854.75E+3Kr-873.64E+1Kr-882.25E+2Kr-891.76E-1 Rev. 13 TABLE 15.7-4 RADIOLOGICAL CONSEQUENCES OF A WASTE GAS DECAY TANK RUPTURE Doses (rem) Exclusion Area Boundary (0-2 hr) Thyroid 3.66E-03 Whole Body 1.31E-01 Low Population Zone Outer Boundary (duration) Thyroid 4.88E-04 Whole Body 1.74E-02 Control Room Thyroid 1.45E-02 Whole Body 2.16E-02 Beta Skin 6.23E-01
Rev. 26
WOLFCREEKTABLE15.7-5PARAMETERSUSEDINEVALUATINGTHERADIOLOGICALCONSEQUENCESOFALIQUIDRADWASTETANKFAILUREI.SourceDataa.Corepowerlevel,MWt3,565 b.Failedfuel,percent1II.AtmosphericDispersionFactorsSeeTable15A-2III.ActivityReleaseDataa.Noblegasactivity,percentoftankcontents100b.Iodinegasactivity,percentoftankcontents1.Boronrecycleholduptank102.HypotheticalLiquidWastetank100c.Tankcontentssubjecttorelease1.BoronrecycleholduptankTable11.1-6(sheet13)2.PrimaryevaporatorbottomsTable11.1-6tank(sheet16)d.Activityreleasedtotheenvironment1.BoronrecycleholduptankIsotope0-2hr(Ci)I-1314.96E-1I-1327.90E-3 I-1331.13E-1I-1347.25E-4I-1352.09E-2 Xe-131m3.35E+2 Xe-133m1.40E+2 Xe-1331.68E+4Xe-135m1.06E-1Xe-1354.40E+1 Xe-1376.97E-3 Xe-1389.38E-2 Kr-83m5.02E-1 Kr-85m4.93 Kr-851.59E+3Kr-879.06E-1Kr-885.80 Kr-893.10E-3Rev.14 WOLFCREEKTABLE15.7-5(Sheet2)2.PrimaryevaporatorbottomstankIsotope0-2hr(Ci)I-1311.92E+01I-1329.939E-24I-1337.464E-03I-1343.192E-61I-1357.190E-09Xe-131m0.000E+00Xe-133m0.000E+00Xe-1330.000E+00Xe-135m0.000E+00Xe-1350.000E+00Xe-1370.000E+00Xe-1380.000E+00Kr-83m0.000E+00Kr-85m0.000E+00Kr-850.000E+00Kr-870.000E+00Kr-880.000E+00Kr-890.000E+00Rev.14 WOLFCREEKTABLE15.7-6RADIOLOGICALCONSEQUENCESOFALIQUIDRADWASTETANKFAILUREDose(rem)BoronRecycleTankExclusionAreaBoundary(0-2hr)Thyroid4.01E-2Whole-body2.48E-2LowPopulationZoneOuterBoundary (duration)Thyroid5.35E-3 Whole-body3.31E-3HypotheticalLiquidWasteTankExclusionAreaBoundary(0-2hr)Thyroid1.49E+00LowPopulationZoneOuterBoundary (duration)Thyroid2.00E-1Rev.14 WOLF CREEK TABLE 15.7-7 PARAMETERS USED IN EVALUATING THE RADIOLOGICAL CONSEQUENCES OF A FUEL-HANDLING ACCIDENT In Fuel Building In Reactor BuildingI. Source Data a. Core power level, MWt 3,565 3,565 b. Radial peaking factor 1.65 1.65 c. Decay time, hours 76 76 d. Number of fuel assem- 1.0 1.2 blies affected
- e. Fraction of fission product gases con-tained in the gap region of the fuel assembly Per R.G. 1.25 and Per R.G. 1.25 and NUREG/CR-5009 NUREG/CR-5009 II. Atmospheric Dispersion Factors See Table 15A-2 See Table 15A-2 III.Activity Release Data a. Percent of affected fuel assemblies gap activity released 100 100 b. Pool decontamination factors
- 1. Iodine 100 100
- 2. Noble gas 1 1 c. Filter efficiency, percent 82.5* 0 d. Building mixing vo-lumes assumed, percent of total volume 0 0 e. Activity release period, hrs 2 2 *NOTE: The postulated fuel handling accident in the Fueling Building was analyzed with a reduced filter efficiency, based upon the single failure assumption that one of the emergency Exhaust Filter-Adsorber units is operating with a failed heater or humidistat. Rev. 20 WOLF CREEK TABLE 15.7-7 (Sheet 2) h. Activity released to the environment Fuel Building Reactor Building Isotope 0-2 hr (Ci) 0-2 hr (Ci)I-131 1.84E+2 8.86E+2 I-133 3.28E+1 1.58E+2 Xe-131m 7.18E+2 8.61E+2 Xe-133m 1.90E+3 2.28E+3 Xe-133 1.10E+5 1.32E+5 Xe-135 1.22E+2 1.45E+2 Kr-85 2.62E+3 3.14E+3 Rev. 20 WOLF CREEK TABLE 15.7-8 RADIOLOGICAL CONSEQUENCES OF A FUEL HANDLING ACCIDENT Dose (rem)
In Fuel Building Exclusion Area Boundary (0-2 hr) Thyroid 1.48E+1 Whole-body 1.72E-1 Low Population Zone Outer Boundary (duration) Thyroid 1.97E+0 Whole-body 2.30E-2 In Reactor Building Exclusion Area Boundary
(0-2 hr)Thyroid 7.09E+1 Whole-body 2.04E-1 Low Population Zone
Outer Boundary (duration) Thyroid 9.46E+0 Whole-body 2.72E-2 Rev. 20 WOLF CREEK 15.8 ANTICIPATED TRANSIENTS WITHOUT SCRAM An ATWS is an anticipated operational occurrence (such as loss of normal feedwater, loss of load, turbine trip, inadvertent control rod withdrawal, loss of AC power, and loss of condenser vacuum) that is accompanied by a failure of the Reactor Protection System (RPS) to shut down the reactor. The most severe ATWS scenarios are those in which there was a complete loss of normal feedwater and the loss of load. The primary safety concern for these transients is the potential for high pressures within the RCS. Based on generic analyses, acceptable consequences would result, that is, RCS pressures less than the pressure (3200 psig) corresponding to the ASME Boiler and Pressure Vessel Code Level C service limit stress criteria, provided that the turbine trips and auxiliary feedwater flow is initiated in a timely manner. Normally, these features would be actuated by the RPS. However, if a common mode failure in the RPS incapacitates AFW flow initiation and/or turbine trip (in addition to prohibiting a scram), then an alternate method of providing AFW flow and turbine trip is required. These two functions are provided by AMSAC, which is required by the final ATWS Rule in 10CFR50.62 (c)(1) for Westinghouse PWRs, as discussed below. The ATWS Rule (10CFR50.62(b)) requires specific improvements in the design and operation of commercial nuclear power facilities to reduce the probability of failure to shut down the reactor following anticipated transients and to mitigate the consequences of an ATWS event. 10CFR50.62 Requirements for Reduction of Risk from Anticipated Transients Without Scram (ATWS) Events for Light-Water-Cooled Nuclear Power Plants, was effective July 26, 1984. Paragraph (c)(6) of the ATWS Rule requires that detailed information to demonstrate compliance with the requirements be submitted to the Director, Office of Nuclear Reactor Regulation (NRR). In accordance with paragraph (c)(6) of the ATWS Rule, the Operating Agent provided information to the NRC by letter, dated March 20, 1987. The letter forwarded the detailed description of the ATWS Mitigation System Actuation Circuitry (AMSAC) proposed for installation at the Wolf Creek Generating Station (WCGS). Supplemental information on the AMSAC design was also submitted to the NRC in letters dated April 16, 1987 and October 5, 1987, for review. WCGS installed equipment (AMSAC) from sensor output to final actuation device, that is diverse from the reactor trip system, to automatically initiate the auxiliary feedwater system and initiate a turbine trip under conditions indicative of an ATWS. On December 16, 1987, the NRC notified the Operating Agent by letter that the staff had completed its review of the submittal and concluded that the AMSAC design for the WCGS was acceptable and in compliance with the ATWS Rule, 10CFR50.62. 15.8-1 Rev. 13 WOLF CREEK APPENDIX 15A ACCIDENT ANALYSIS RADIOLOGICAL CONSEQUENCES EVALUATION MODELS AND PARAMETERS 15A.1 GENERAL ACCIDENT PARAMETERS This section contains the parameters used in analyzing the radiological consequences of postulated accidents. Table 15A-1 contains the general
parameters used in all the accident analyses. For parameters specific only to
particular accidents, refer to that accident parameter section. The site
specific, ground-level release, short-term dispersion factors (for accidents, ground-level releases are assumed) are based on Regulatory Guide 1.145 (Ref. 1)
methodology and represent the worst of the 5 percent overall site meteorology
and the 0.5 percent worst-sector meteorology and these are given in Table 15A-2 (see Section 2.3.4 for additional details on meteorology). The core and gap
inventories are given in Table 15A-3. The thyroid (via inhalation pathway), beta skin, and total-body (via submersion pathway) dose factors based on
References 2, 3a and 3b are given in Table 15A-4. 15A.2 OFFSITE RADIOLOGICAL CONSEQUENCES CALCULATIONAL MODELS This section presents the models and equations used for calculating the integrated activity released to the environment, the accident flow paths, and
the equations for dose calculations. Two major release models are considered:
(1) a single holdup system with no internal cleanup and (2) a holdup system
wherein a two-region spray model is used for internal cleanup. 15A.2.1 ACCIDENT RELEASE PATHWAYS
The release pathways for the major accidents are given in Figure 15A-1. The accidents and their pathways are as follows: LOCA: Immediately following a postulated loss-of-coolant accident (LOCA), the release of radioactivity from the containment is to the environment with the containment spray and ESF systems in full operation. The release in this case is calculated using Equation (8) which takes into account a two-region spray model within the containment. The release of radioactivity to the environment due to assumed ESF system leakages in the auxiliary building will be via ESF filters and is calculated using Equation (5). In addition, the release of radioactivity to the environment due to assumed ECCS boundary valves leakage through RWST is calculated using Equation (11). 15A-1 Rev. 14 WOLF CREEK WGDTR: The activity release to the environment due to waste gas decay tank rupture (WGDTR) will be direct and unfiltered, with no holdup. The release
pathway is A'-D. The total activity release in this case is therefore assumed
to be the initial source activity itself. FHA: The release to the environment due to a fuel handling accident (FHA) in the fuel building is via filters following the actuation of the emergency exhaust system. The release pathway is B-C-D. Since the release is calculated without any credit for holdup in the fuel building, the total release will be the unfiltered release for the first minute plus the product of the initial activity and the filter nonremoval efficiency fraction (for noble gases, the
nonremoval efficiency fraction is 1). The release of radioactivity to the
environment due to FHA inside the containment is direct and unfiltered, via the
A-D pathway, and occurs over a two-hour period (actually, the release is via
the non-safety graded filters). The release is calculated using Equation (8)
based on a two-region spray model. CAE: Radioactivity release to the environment due to the control assembly ejection (CAE) accident is direct and unfiltered. The releases from the
primary system are calculated using equation 5 which considers holdup in the single-region primary system (the spray removal is not assumed); the secondary (steam) releases via the relief valves are calculated without any holdup. The pathways for these releases are A-D and A'-D. MSLB, SGTR: Radioactivity releases to the environment due to main steam line break (MSLB) or steam generator tube rupture (SGTR) accidents are direct and
unfiltered with no holdup via the A'-D pathway. The activity release calculations for these accidents are complex, involving spiking effects, time-
dependent flashing fractions, and scrubbing of flashed activities; the release
calculations are described in those sections that address these accidents. 15A.2.2 SINGLE-REGION RELEASE MODEL It is assumed that any activity released to the holdup system instantaneously diffuses to uniformly occupy the system volume. The following equations are used to calculate the integrated activity released from postulated accidents. A 1 (0) = initial source activity at time t o , Ci A 1 (t) = source activity at time t seconds, Ci A 1 (t) = A 1 (0)e- 1 t (1) 15A-2 Rev. 19 WOLF CREEK where 1 = total removal constant from primary holdup system, sec -111dr (2) where d = decay removal constant, sec -1 1 = primary holdup leak or release rate, sec -1 r = internal removal constant (i.e., sprays, plateout, etc.), sec -1 Thus, the direct release rate to the atmosphere from the primary holdup system RtAt u 11 (3) Rt u unfiltered release rate (Ci/sec) The integrated activity release is the integral of the above equation. IARtRtAoe u t o t o t 11 1 (4) This yields: IARtAoe t111 1 1/ (5) 15A.2.3a TWO-REGION SPRAY MODEL IN CONTAINMENT (LOCA) A two-region spray model is used to calculate the integrated activity released to the environment. The model consists of a sprayed and unsprayed region in
containment and a constant mixing rate between them. As it is assumed that there are no sources after initial release of the fission products, the remaining processes are removal and transfer so that the
multivolume containment is described by a system of coupled first-order
differential equations of the form dA dt = - -A - Q Ai Vi +Q Ai Vi iiji j=1 K i=1-n-1 i=1n-1 i (6) 15A-3 Rev. 14 WOLF CREEK where A i = fission product activity in volume i, Ci n = number of volumes considered in the model Q il = transfer rate from volume i to volume l, cc/sec V i = volume of the ith compartment, cc l ij = removal rate of the jth removal process in volume i, sec -1 K i = total number of removal processes in volume i This system of equations is readily solved if the coefficients are known. For a two-region model, the above system reduces to dA 1 dt = -j=1 K 1 l 1j A 1 - Q 12 A 1 V 1 + Q 21 A 2 V 2 (6a) dA 2 dt = -j=1 K 1 l 2j A 2 - Q 21 A 2 V 2 + Q 12 A 1 V 1 (6b) Upon solving this coupled set of differential equations numerically, the release rate of activity is found from R(t) = 1 A(t) (7) The integrated activity released from time t 0 - t 1 is shown in the following equation which is solved numerically. IAR = t 0 t 1 R(t)dt (8) 15A-4 Rev. 14 WOLF CREEK 15A.2.3b TWO-REGION RELEASE MODEL FOR LEAKAGE THROUGH RWST It is assumed that the activity released to the holdup system (in this case, the containment recirculation sump) instantaneously diffuses to uniformly occupy the sump volume. Removal mechanisms from the sump include decay and release (i.e., leakage) to the RWST. The release rate from the RWST to the environment is given by R 2 (t) = f A 2 (t) (9) where R 2 (t) = the unfiltered release rate from the RWST vent, Ci/sec f = assumed percent of radioiodine released to the RWST that becomes airborne = release rate constant for leakage from the RWST to the environment, based on an assumed leak rate from the sump that is uniformly mixed in the RWST volume, sec -1 A 2(t) = RWST activity, Ci The RWST activity can be calculated as A 2(t) = Activity in RWST + Activity from sump - Activity released to environment = A 2 (t-t)e- dt+ 1 A 1 (t-t)t-R 2 (t-t)t (10) where 1 = release rate constant for leakage from the uniformly mixed sump to the RWST, based on an assumed leak rate from the sump to the RWST, sec-1 A 1(t) = containment sump activity, Ci d = decay removal constant, sec -1 The integrated release from the RWST is given by IAR 2 (t) = 0 tR 2 (t)dt = f 0 tA 2 (t)dt (11) and is calculated numerically by using Equation (10). 15A-5 Rev. 14 WOLF CREEK 15A.2.4 OFFSITE THYROID DOSE CALCULATION MODEL Offsite thyroid doses are calculated using the equation: D TH =i DCF Thij (IAR)ij (BR)j (c/Q)j (12) where (IAR) ij = integrated activity of isotope i released* during the time interval j in Ci and (BR)j = breathing rate during time interval j in meter 3/second (c/Q)j = offsite atmospheric dispersion factor during time interval j in second/meter 3 (DCF) Thi = thyroid dose conversion factor via inhalation for isotope i in rem/Ci DTh = thyroid dose via inhalation in rems
- No credit is taken for cloud depletion by ground deposition and radioactive decay during transport to the exclusion area boundary or the outer boundary of
the low-population zone. 15A-6 Rev. 14 WOLF CREEK 15A.2.5 OFFSITE TOTAL-BODY DOSE CALCULATIONAL MODEL Assuming a semi-infinite cloud of gamma emitters, offsite total-body doses are calculated using the equation: D TB =i DCF gij (IAR)ij (c/Q)j where (IAR) ij = integrated activity of isotope i released* during the j th time interval in Ci and (c/Q) j = offsite atmospheric dispersion factor during time interval j in second/meter 3 (DCF) gi = total-body gamma dose conversion factor for the i th isotope in rem-meter 3/Ci-sec D TB = total-body dose in rems 15A.3 CONTROL ROOM RADIOLOGICAL CONSEQUENCES CALCULATIONAL MODELS Only radiation doses to a control room operator due to postulated LOCA are presented in this chapter since a study of the radiological consequences in the
control room due to various postulated accidents indicate that the LOCA is the limiting case. 15A.3.1 INTEGRATED ACTIVITY IN CONTROL ROOM Make-up air is brought into the control room via the control room filtration system which draws in air from the control building. Outside air is brought
into the control building through safety grade filters via the control room
pressurization fan. Some unfiltered air also may leak into the control
building via an assumed inleakage rate. The activity concentrations at the
control building intake for each time interval are found by multiplying the
activity release to the environment by the appropriate c/Q for that time
interval. The flow path model is shown below.
- No credit is taken for cloud depletion by ground deposition and radioactive decay during transport to the exclusion area boundary or the outer boundary of
the low-population zone. 15A-7 Rev. 14 WOLF CREEK e n v i r o n m e n t intake inleakage filter F1 F2 control building control room outleakage (F1+F2+ F6)-(1-)(F3+F4)filter F3 F4 F5 (F3+F4+F6 F3+F5 (1-)(F3+F4+F6) F6 Once activity is brought into the control building, mixing within the control building is afforded by the control room pressurization fan. The control room
filtration system fan takes air from the control building and the control room (recirculation) and discharges to the control room through the control room filtration safety grade filters. The radiological analysis input parameters
are provided in Table 15A-1. The control room ventilation isolation signal (CRVIS) starts both trains of the control room pressurization system and the control room filtration system. For the determination of dose to control room personnel, the worst single failure
has been ascertained to be the failure of the filtration fan in one of the two
filtration system trains. Prior to operator action, a potential pathway would exist allowing air from the control building to enter the control room, bypassing the control room filtration filters. Operator action is required to ensure no bypass pathways then exist for unfiltered air to enter the control room. Owning to this single failure of the control room filtration fan, the assumed
failure of one of the two containment spray (CS) trains, and two of the four
hydrogen mixing subsystem fans, inherent in the LOCA analysis parameters given in Table 15.6-6 should not be applied in this analysis. With both trains of CS and four hydrogen mixing fans operating, more volumetric coverage of the
containment spray and more mixing between the new sprayed and unsprayed regions
would be expected, thereby giving much greater iodine removal within the
containment atmosphere. However, the doses to control room personnel have been based on the LOCA analysis parameters given in Table 15.6-6. 15A-8 Rev. 14 WOLF CREEK The activity in the control building and control room is calculated by solving the following coupled set of first order differential equations. dAt dtFFQRtAtAt CBCRCB11243dAt dtAtAtFQRt CRfuCBCR13346where A CB (t) = activity in control building at time t, curies A CR (t) = activity in control room at time t, curies = filter efficiency, fraction F 1 = filtered intake rate, meter 3/sec F 2 = unfiltered intake (inleakage), meter 3/sec/Q = atmospheric dispersion factor, sec/meter 3 R(t) = activity release rate in Ci/sec as given in Equation 3 of Section 15A.2.2 or Equations 7 and 9 of Sections 15A.2.3a and 15A2.3b 3 = d + 3 + 3f + 3u , total removal rate from the control building, sec -1 d = isotopic decay constant, sec -1 3 = outleakage to atmosphere from the control building (= (F1 + F2 + F 6 - (1-)(F3 +F4))/V CB with V CB being control building mixing volume in meter 3), sec -1 3f = filtered flow from control building into control room (=F 3/V CB , F 3 in meter 3/sec), sec -1 3u = unfiltered flow from control building into control room (=F 4/V CB , F 4 in meter 3/sec), sec -1 15A-9 Rev. 14 WOLF CREEK 4 = d + r + 4 , total removal rate from the control room, sec -1 r = recirculation removal rate (= F 5/V CR with F 5 being recirculation flow rate in meter 3/ sec through filter with efficiency and V CR being control room volume in meter 3), sec -1 4 = leakage to control building from the control room (=[F 3 + F 4]/V CR), sec-1= fraction of control room outleakage which returns to the control building mixing volume F 6 = control room direct unfiltered intake, meter 3/sec Upon solving this coupled set of differential equations, the integrated activity in the control room (IA CR) is determined by the expression IA CR(t) =0 t A CR (t)dt This IA CR (t) is used to calculate the doses to the operator in the control room. This activity is multiplied by an occupancy factor which accounts for the time fraction the operator is in the control room. 15A.3.2 CONTROL ROOM THYROID DOSE CALCULATIONAL MODEL
Control room thyroid doses via inhalation pathway are calculated using the following equation: D Th-CR = BR V CRi DCF Thij (IA CRij) x O j where D Th-CR = control room thyroid dose in rem and BR = breathing rate assumed to be always 3.47 x 10 -4 meter 3/second V CR = volume of the control room in cubic meters DCF Thi = thyroid dose conversion factor for adult via inhalation in rem/Ci for isotope i 15A-10 Rev. 14 WOLF CREEK IA CRij = integrated activity in control room in Ci-sec for isotope i during time interval j O j = control room occupancy fraction during time interval j
15A.3.3 CONTROL ROOM BETA-SKIN DOSE CALCULATIONAL MODEL The beta-skin doses to a control room operator are calculated using the following equation: D b-CR =1 V CRi DCF bij (IA CRij) X O j where D b-CR and DCF bi are the beta-skin doses in the control room in rem and the beta-skin dose conversion factor for isotope i in rem-meter 3/Ci-sec, respectively. The other symbols are explained in Section 15A.3.2. 15A.3.4 CONTROL ROOM TOTAL-BODY DOSE CALCULATION Due to the finite structure of the control room, the total-body gamma doses to a control room operator will be substantially less than what they would be due
to immersion in an infinite cloud of gamma emitters. The finite cloud gamma
doses are calculated using Murphy's method (Ref. 4) which models the control
room as a hemisphere. The following equation is used: D TB-CR = 1 V CR (GF)i DCF gij (IA CRij) X O j where GF = dose reduction due to control room geometry factor GF = 1173/(V 1)0.338 V 1 = volume of the control room in cubic feet D TB-CR = total-body dose in the control room in rem, and other quantities have been defined in subsections 15A.2.5 and 15A.3.2. 15A-11 Rev. 14 WOLF CREEK 15A.3.4.1 Model for Radiological Consequences Due to Radioactive Cloud External to the Control Room This dose is calculated based on the semi-infinite cloud model which is modified using the protection factors described in Section 7.5.4 of Reference 5 to account for the control room walls. 15A.4 REFERENCES
- 1. USNRC Regulatory Guide 1.145, "Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear
Power Plants," August 1979.
- 2. USNRC Regulatory Guide 1.109, Rev. 1, "Calculation of Annual Doses to Man from Routine Releases of Reactor Effluents for
the Purpose of Evaluating Compliance with 10 CFR Part 50
Appendix I," October 1977. 3a. Kocher, D.C., "Nuclear Decay Data for Radionuclides Occurring in Routine Releases from Nuclear Fuel Cycle Facilities," ORNL/NUREG/TM-102, August 1977. 3b. Berger, M.J., "Beta-Ray Dose in Tissue-Equivalent Material Immersed in a Radioactive Cloud," Health Physics, Vol. 26, pp. 1-12, January 1974.
- 4. Murphy, K.G. and Campe, K.M., "Nuclear Power Plant Control Room Ventilation System Design for Meeting General Criterion 19," Paper presented at the 13th AEC Air Cleaning Conference, August 1974.
- 5. "Meteorology and Atomic Energy 1968," D. H. Slade (ed.), USAEC Report, TID 24190, 1968. 15A-12 Rev. 14 WOLFCREEKTABLE15A-1PARAMETERSUSEDINACCIDENTANALYSISI.General1.Corepowerlevel,Mwt35652.Full-poweroperation,dayspercycle5103.Numberoffuelassembliesinthecore1934.Maximumradialpeakingfactor1.65 5.Percentageoffailedfuel1.06.Steamgeneratortubeleak,lb/hr500II.Sources1.Coreinventories,CiTable15A-32.Gapinventories,CiTable15A-3 3.Primarycoolantspecificactivities,Ci/gmTable11.1-54.Primarycoolantactivity,technicalspecificationlimitforiodines-I-131doseequivalent,µCi/gm1.05.Secondarycoolantactivitytechnicalspecificationlimitforiodines-I-131doseequivalent,µCi/gm0.1III.ActivityReleaseParameters1.Freevolumeofcontainment,ft 32.5x10 62.Containmentleakratei.0-24hours,%perday0.2ii.after24hrs,%perday0.1IV.ControlRoomDoseAnalysis(forLOCA)1.Controlbuildingi.Mixingvolume,cf239,000 ii.Filteredintake,cfmPriortooperatoraction(0-1.5hours)>1350Afteroperatoraction(1.5hours-720hours)>675iii.Unfilteredinleakage,cfm<300iv.Filterefficiency(allformsof iodine),%95Rev.14 WOLFCREEKTABLE15A-1(Sheet2)2.Controlroomi.Volume,cf100,000ii.Filteredflowfromcontrolbuilding,cfm<550(*)iii.Unfilteredflowfromcontrolbuilding,cfmPriortooperatoraction<550(*)(0-1.5hours)Afteroperatoraction(1.5hours-720hours)0iv.Filteredrecirculation,cfm>1250v.Filterefficiency(allformsofiodine),%95(*)NOTE:Flowspossiblepertrainwithtwotrainsinoperation.Eachtrainisbalancedfor400cfm.3.TotalFlowSummary(Filteredplusunfiltered)i.0-1.5hoursa.ControlRoomPressurization>1650(**)b.ControlRoomFiltration<1100ii.1.5hours-720hoursa.ControlRoomPressurization>975(**)b.ControlRoomFiltration<550(**)NOTE:Includes300cfmofunfilteredControlBldginleakage.4.EmergencyExhaustFilterAdsorberUnit90Efficiency(allformsofiodine),%V.Miscellaneous1.Atmosphericdispersionfactors,/Qsec/m 3Table15A-22.Doseconversionfactorsi.totalbodyandbetaskin,rem-meter 3/Ci-secTable15A-4ii.thyroid,rem/CiTable15A-43.Breathingrates,meter 3/seci.controlroomatalltimes3.47x10
-4ii.offsite0-8hrs3.47x10 24hrs1.75x10 -424-720hrs2.32x10 -44.Controlroomoccupancyfractions0-24hrs1.0 24-96hrs0.6 96-720hrs0.4Rev.14 WOLF CREEK TABLE 15A-2 LIMITING SHORT-TERM ATMOSPHERIC DISPERSION FACTORS
(/Qs) FOR ACCIDENT ANALYSIS (sec/meter
- 3) Location Type/
Time Interval/Q (hrs) (Sec/Meters
- 3) Site boundary 0-2 1.5E-4 Low-population zone 0-8 2.0E-5
8-24 1.3E-5
24-96 5.4E-6
96-720 1.5E-6 Control room (via containment leakage) 0-8 5.3E-4
8-24 3.6E-4
24-96 6.6E-5
96-720 0 Control room (via unit vent exhaust) 0-8 1.lE-4
8-24 6.8E-5
24-96 1.7E-5
96-720 0 Rev. 0 WOLFCREEKTABLE15A-3FUELANDRODGAPINVENTORIES-CORE(Ci) CoreIsotopeFuelGapI-1319.46E+7 9.46E+6I-1321.37E+8 1.37E+7I-1331.95E+8 1.95E+7I-1342.15E+8 2.15E+7I-1351.83E+8 1.83E+7Kr-83m1.24E+7 1.24E+6Kr-85m2.67E+7 2.67E+6Kr-851.02E+6 3.05E+5Kr-875.16E+7 5.16E+6Kr-887.28E+7 7.28E+6Kr-898.94E+7 8.94E+6Xe-131m1.01E+6 1.01E+5Xe-133m6.06E+6 6.06E+5Xe-1331.95E+8 1.95E+7Xe-135m3.77E+7 3.77E+6Xe-1354.70E+7 4.70E+6Xe-1371.71E+8 1.71E+7Xe-1381.64E+8 1.64E+7*Gapactivityisassumedtobe10percentofcoreactivityforallisotopesexceptforKr-85;forKr-85itisassumedtobe30percentofthecoreactivity.However,gapactivityforI-131isassumedtobe12%insteadof10%ofthecoreactivityforfuelhandlingaccident,lockedrotoraccidentandrodejectionaccidentanalysestoaccountforextendedburnupfuel.Rev.14 WOLF CREEK TABLE 15A-4
DOSE CONVERSION FACTORS USED IN ACCIDENT ANALYSIS Total Body Beta Skin Rem-meter 3 Rem-meter 3 Thyroid Nuclide Ci-sec Ci-sec Rem/Ci I-131 8.72E-2 3.17E-2 1.49E+6 I-132 5.13E-1 1.32E-1 1.43E+4 I-133 1.55E-1 7.35E-2 2.69E+5
I-134 5.32E-1 9.23E-2 3.73E+3
I-135 4.21E-1 1.29E-1 5.60E+4
Kr-83m 2.40E-6 0 NA Kr-85m 3.71E-2 4.63E-2 NA Kr-85 5.llE-4 4.25E-2 NA
Kr-87 1.88E-1 3.09E-1 NA
Kr-88 4.67E-1 7.52E-2 NA
Kr-89 5.27E-1 3.20E-1 NA
Xe-131m 2.91E-3 1.51E-2 NA
Xe-133m 7.97E-3 3.15E-2 NA
Xe-133 9.33E-3 9.70E-3 NA Xe-135m 9.91E-2 2.25E-2 NA
Xe-135 5.75E-2 5.90E-2 NA
Xe-137 4.51E-2 3.87E-1 NA
Xe-138 2.80E-1 1.31E-1 NA Rev. 0 CONTAINMENT ASTEAM VENT &SAFETY VALVESRADWASTE BUILDINGAUXILIARY BUILDINGOR RWST A'FUEL BUILDING BATMOSPHERE D CCONTROL ROOMLOCA AND CAELOCA, SGTR, MSLB, WGDTRCAE AND FHA IN CONTAINMENTFHA IN FUEL BUILDINGWOLF CREEK UPDATED SAFETYANALYSIS REPORTFIGURE 15.A-1RELEASE PATHWAYSREV. 19}}