ML15117A261

Summary of 941012 Meeting W/Dpc Re Status of PRA Being Performed for Keowee Hydrostation.Forwards List of Meeting Attendees & Licensee Handout

ML15117A261
Person / Time
Site:	Oconee
Issue date:	11/14/1994
From:	Wiens L Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 9411170291
Download: ML15117A261 (87)

Text

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0 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November 14, 1994 Licensee:

Duke Power Company Facility: Oconee Nuclear Station, Units 1, 2, and 3

SUMMARY

OF OCTOBER 12, 1994, MEETING WITH DUKE POWER COMPANY ON KEOWEE PROBABILISTIC RISK ASSESSMENT PROJECT On October 12, 1994, NRC staff members met with representatives of Duke Power Company (DPC) to discuss the status of the Probabilistic Risk Assessment (PRA) being performed for the Keowee hydrostation. A list of meeting attendees is included as Enclosure 1. Copies of licensee handouts are included as.

The licensee's presentation opened with an overview of the project, including the purpose and objective of the analysis, a description of the project scope and level of detail, the project team organization, and the project schedule.

In response to a staff question, the licensee explained that the analysis did not include external events, and that the external events would be covered under the IPE for External Events. The presentation also covered a brief description of the PRA process and the identification of data for the analysis. As a follow-up to a question from the previous meeting on the status of this project, the licensee stated that the decision had been made to integrate the results of this PRA study into the IPE. A number of other questions concerning clarification of the PRA process being used by DPC were also discussed. The licensee presented the preliminary results of the Keowee reliability study. The licensee then presented preliminary results for AC power reliability and the effect on core melt frequency from integrating the preliminary PRA results into the IPE. The Keowee reliability results were analyzed for the delivery of power to the startup transformer for the overhead path or transformer CT-4 for the underground path. The licensee's preliminary results indicated that the probability of core damage resulting from a loss of off-site power was comparable to the IPE results for this event.

9411170291 941114 PDR ADOCK 05000269 PPDR NB-R TTRc

2 -

November 14, 1994 At the conclusion of the meeting, the NRC staff requested that the licensee provide the most recent fault tree base case models for both the systems and the integrated model.

In addition, cut sets were requested to show results of the base case and sensitivity studies. The licensee was requested to perform an analysis and provide the cut sets for one Keowee unit in maintenance and the other unit paralleled to the electrical off-site grid. The licensee agreed to each of these requests.

/s/

Leonard A. Wiens, Project Manager Project Directorate 11-3 Division of Reactor Projects -

I/Il Docket Nos. 50-269, 50-270, and 50-287

Enclosures:

1. List of Meeting Attendees

2. Licensee Handouts cc w/enclosures:

See next page DISTRIBUTION E;Do.c ketYJ-1 OGC, 0-15 B18 PUBLIC E. Jordan, T-4 D18 PDII-3 R/F ACRS (4), TWF W. Russell/F. Miraglia, 0-12 G18 G. Tracy, EDO, 0-17 G21 R. Zimmerman, 0-12 Gl8 B. Boger, Ru S. Varga M. Sinkule, Ru J. Zwolinski A. Thadani, 0-12 G18 D. Nguyen, 0-7 E4 V. Beaston, 0-7 E4 F. Burrows, 0-7 E4 W. Swenson, 0-10 E4 M. Virgilio, 0-8 E2 S. Rosenberg, 0-10 E4

3. Shackelford, RJT To receive a copy of this document, indicate in the box:

"C" = Copy without attachment/enclosure "E" = Copy with attachment/enclosure "N"

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2 -

November 14, 1994 At the conclusion of the meeting, the NRC staff requested that the licensee provide the most recent fault tree base case models for both the systems and the integrated model. In addition, cut sets were requested to show results of the base case and sensitivity studies. The licensee was requested to perform an analysis and provide the cut sets for one Keowee unit in maintenance and the other unit paralleled to the electrical off-site grid. The licensee agreed to each of these requests.

Leonard A. Wiens, Project Manager Project Directorate 11-3 Division of Reactor Projects -

I/Il Docket Nos. 50-269, 50-270, and 50-287

Enclosures:

1. List of Meeting Attendees

2. Licensee Handouts cc w/enclosures:

See next page

Duke Power Company Oconee Nuclear Station cc:

A. V. Carr, Esquire Mr. Ed Burchfield Duke Power Company Compliance 422 South Church Street Duke Power Company Charlotte, North Carolina 28242-0001 Oconee Nuclear Site P. 0. Box 1439 J. Michael.McGarry, III, Esquire Seneca, South Carolina 29679 Winston and Strawn 1400 L Street, NW.

Ms. Karen E. Long Washington, DC 20005 Assistant Attorney General North Carolina Department of Mr. Robert B. Borsum Justice Babcock & Wilcox P. 0. Box 629 Nuclear Power Division Raleigh, North Carolina 27602 Suite 525 1700 Rockville Pike Mr. G. A. Copp Rockville, Maryland 20852 Licensing -

EC050 Duke Power Company Manager, LIS 526 South Church Street NUS Corporation Charlotte, North Carolina 28242-0001 2650 McCormick Drive, 3rd Floor Clearwater, Florida 34619-1035 Dayne H. Brown, Director Division of Radiation Protection Senior Resident Inspector North Carolina Department of U. S. Nuclear Regulatory Commission Environment, Health and Route 2, Box 610 Natural Resources Seneca, South Carolina 29678 P. 0. Box 27687 Raleigh, North Carolina 27611-7687 Regional Administrator, Region II U. S. Nuclear Regulatory Commission Mr. J. W. Hampton 101 Marietta Street, NW. Suite 2900 Vice President, Oconee Site Atlanta, Georgia 30323 Duke Power Company P. 0. Box 1439 Max Batavia, Chief Seneca, South Carolina 27679 Bureau of Radiological Health South Carolina Department of Health and Environmental Control 2600 Bull Street Columbia, South Carolina 29201 County Supervisor of Oconee County Walhalla, South Carolina 29621

MEETING ATTENDEES 0

KEOWEE PROBABILISTIC SAFETY ASSESSMENT STATUS MEETING October 12, 1994 NAME ORGANIZATION Len Wiens NRC/NRR/PDII-3 Duncan Brewer Duke Power/PRA Mike Barrett Duke Power/PRA P. M. Abraham Duke Power/PRA Duc Nguyen EELB/NRR Homayoon Dezfulz SCIENTECH INC V. Beaston NRR/DE/EELB Ken Canady Duke Power/Nuclear Eng.

Fred Burrows EELB/NRR Ed Burchfield Duke/ONS/Regulatory Compliance Clay A. Little Duke/ONS/Elec. Eng.

Warren Swenson NRR/SPSB Marty Virgilio NRC/DSSA Stacey Rosenberg NRR/DSSA/SPSB Frank Quinn SCIENTECH Inc.

Herb Berkow NRC/NRR\\PDII-3 Jeff Shackelford NRC/RII/DRS/OPS Reed Severance Duke Power/ONS/Mech. Sys. Eng.

Jeff Rowell Duke Power/ONS/Elect. Power Sys.

Michael Bailey Duke Power/ONS/Regulatory Compliance ATTACHMENT 1

Keowee PRA NRC-Duke Meeting October 12, 1994

Agenda 8:30 Introduction (P. M. Abraham) 8:45 Overview of KPRA (Duncan Brewer) 9:15 KPRA Analysis And Results (Mike Barrett) 10:30 Break 10:50 AC Power Reliability Results (Duncan Brewer) 11:20 AC Power Core Melt Frequency Results (Duncan Brewer) 12:00 Break 1:00 Questions and Answers Keowee PRA

Keowee PRA Overview of Keowee PRA Process By Duncan Brewer Page 3

Outline

• Purpose and Objects of the Study

• Project Plan

• Project Team

• Identification of Data Component Failure Data Common Cause Data Human Reliability Data Keowee PRA Page 4

Objectives of the Study To Develop An Analytical Model Of The Keowee Hydro Station To Integrate the Keowee Model into the Oconee PRA Models for AC Power and Core Damage Frequency To Obtain An Estimate Of The Reliability Of Keowee As An Emergency Power Source, To Determine Keowee's Importance to AC Power Reliability, To Determine Keowee's Importance to Core Damage Frequency Keowee PRA Page 5

Objectives of the Study To Compare the Fstimated Reliability to the Observed Reliability During Normal Operation, Emergency Tests and Functional Tests The Insights Gained From This Analysis Will Be Used To Complement Efforts Which Are Currently Underway To Address Keowee Reliability Concerns Keowee PRA Page6

Project Scope Utilized PRA Methods Such As Fault Trees, Reliability Data, Success Criteria, And Modeling Of Appropriate Human Actions.

The Required Mission Of The Keowee Hydro Station was To Start And Run To Provide Emergency Power To Oconee For All Probabilistically Significant Scenarios Resulting From Internal Initiating Events.

Keowee PRA Page 7

Project Scope The Model Includes All Important Components At A Level Appropriate For Gathering Statistically Significant Data.

Support Systems Important To The Operation Of Keowee Were Also Modeled.

Keowee PRA Paze 8

Project Team Organization Team Included System Analysts, Data Analysts, a Human Reliability Analyst, a Common Cause Analyst, and Plant Support Personnel 10 Members from Duke, One Outside Consultant Used for Independent Review Keowee PRA Page 9

Task List and Schedule Plant Familiarization 2/94 Develop System Models 6/94 Develop Reliability Data 6/94 Solve the Fault Tree Models 7/94 Analysis of Results 9/94 Documentation 12/94 Peer Review (Throughout Project)

Actions 6/95 Keowee PRA Page 10

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Identification of Data Component Failure Data Plant Specific Data was Collected for all Comp onents in the Model Failure Data Was Collected by Review of Operator Logs and Keowee Work Requests Demands and Run Hours for the Period of Record Were Estimated by the System Analysts Generic Data was Developed from Multiple Sources of Generic Data Keowee PRA Page 12

Identification of Data Component Failure Data The Data Base Used For the Solution and Sensitivity Studies was a Bayesian Updated Combination of the Generic and Plant Specific Data We Retained the Ability to Calculate the Results with Generic Data, Plant Specific Data, or the Combined Data Keowee PRA Page 13

Keowee PRA Plant Specific Data Collection Process Review Relevent Data Sources Keowee Operator Logs Oconee Reactor Operators Logs Keowee Switchboard Logs Work Request Database PIP Database PIR Database IIR Database LER Database Expert Opinion Jocossee Data Compile Plant Specific Data Maintenance Develop Numbers Develop Ust of Data for Unit Starts, Component and Run Time and Unit Failures Total Time Plant Specific Data Plant Specific Data For Tpe Code Development For Basic Event Development

Print BE report from CAFTA Import into Excel and sort by tree, failure mode and name Develop list of Develop numbers Develop any special Determine the Review sources of failures for normal anl demand numbers or denominator type generic failure rates emergency (hot vs.

exposure times (start, run, cold) starts, run continuous, etc.)

times, available times, and total time Compile plant-Compile generic specific failure ratesi failure rates s C fI Ie Perform Bayesian Update on failure rates Create (3) type code databases Keowee Reliability Assessment Type Code Development Flow Chart Page 15

Identification of Data Common Cause Data Objective - Qualitatively And Quantitatively Evaluate Potential Common Cause Failure Modes Of Keowee Reviewed Operating Experience and System Models to Determine Appropriate Events Events Included at Both the System and Component Level Used EPRI CCDAT Software Keowee PRA Page 16

Keowee CCF Assessment Process@

Start Problem Definition and Information Collection:

,-Logic7Model;,

Plont.& Systems PIP/PIR/lIR/LERs, Operator SD'-Development Famlilarizcition Logs. Previous Studies/Repo rs 1.2 & 1.3 1.1 Review Keowee Develop List of Post Operating History CCF Events Determine Level of CCF Qualitative CCF Analysis Modeling 2-1 Develop Preliminary CCF Data Classification and Basic Events Screening 3.1 3.3 Quantitative Screening V

Analysis (If necessary) 2-2 Perform Detailed Review CCF Modeling N

Quantification for Modeled CCF Events 3.2 & 3.4 Provide KPRA Report Document CCF Analysis Section on CCF Analysis Techniques and Assumptions 4.3 4.1

~eview Rsultidid p evelopnsi 4.2 Legend End

-CCF Assessment Activities

- Concurrent KPRA Activities 0.0 - indicates corresponding step #

from NUREG/CR-4780 Rg. 2-1 Revised 5/19/94 Figure X-1

Identification of Data Human Reliability Data Reviewed Operating Experience Reviewed System Models Determined Appropriate Human Error Events Modeled Pre-initiator Errors, Post Initiator Errors and Recovery Errors Also, Performed a Qualitative Review for Efrors of Commission Keowee PRA Page 18

Identification of Data Human Reliability Data Used NUREG/CR-1278 (THERP) Method to Quantify Pre-initiator Errors Used EPRI TR-100259 "Decision Tree" Method to Quantify Post Initiator Errors Keowee PRA Page 19

Keowee PA Hurnan Reliability fnalysis Initial Walkdown and Interviews Group Training Review of Industry and Keowee Experience Review of Procedures Development of System Models Post-Initiatorr Events Post-InitPre-initiatorter vent DDetermined Characterization and Quantification solve Recoveries Determined Review Documentation'

Keowee PRA Reliability Analysis and Results Mike Barrett Page 21

ACB -3 CT4 TG2 TG1 Spilway PCB-9

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KOT ACB - 1 Keowee River Oconee 230Kv Switchyard yello bus Startup Transformer CT3

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Keowee Generator System Schematic Drw. PMA pgI ( 06/21/94 )Rev. 4 Page 22

Ue Keowee Overview Keowee Systems Excitation System Air Circuit Breakers Auxiliary AC Power Auxiliary DC Power Generator Keowee Start-up Controls Keowee PRA PageJ 23

Keowee Overview (cont'd)

Keowee Systems (cont'd)

Turbine Governor High Pressure Oil System Governor Air System Governor Oil System Guide Bearing Oil System Turbine Sump System Keowee PRA Page 24

Keowee Overview (cont'd)

Switchyard and Oconee Components and Systems Underground Cable Transformer CT4 Switchyard DC Power System External Grid Trouble Protection System Switchyard Power Circuit Breakers Transformer CT3 Keowee PRA Page 25

Modeling OL,. Atives Address all potential modes of operation of the Keowee units Include all components/systems necessary for the emergency operation of the Keowee units Include in the models the important failure modes that have been experienced 0

Keowee PRA Pane 26

Modeling (cont'd)

Scope Keowee components important for Keowee to provide emergency power to Oconee The underground path up to and including CT4 The overhead path up to and including CT3 Switchyard isolation logic Keowee PRA Page 27

Modeling (cont'd) 14 Individual Fault Trees High Level Logic Model 13 System/Component Trees Keowee PRA Page 28

Modeling (cont'd)

High Level Logic Model Combines the individual sytem/component failures into an overall Keowee power supply failure Factors in the various operating configurations of the Keowee units Provides intermediate gate results for determining the reliability of individual units/paths Keowee PRA Page 29

Keowee Fault Tree Overview High Level Logic Tree (K)

Governor &

Generator Keowee Air Circuit Excitation Power Path Turbine Tree.

Start Tree Breaker Tree Tree Tree (W (G)

()Tree (A)

(E)

(S)

Guide Auxiliar Bearing Oil Power Tree Tree (B)

(X)

Cooling y

EGTPS Tree Water TreeT (F)P3 Governor Oil

& Air Tree (0)

Turbine Swyd DC L-4 ump reePower Tree (P)

(D)

Page 30

Oconee Emergency Power From Keowee Fails KEOWTOP Omonee Emergency Oconee Emergency Power Via The Power Via The Underground Path Overhead Path Fails Fails UNDERO OVERO Pag 7 OcneEVmergenc Keowee Failure De Uot v eweUnit High r LVTe Loioe Pageo 1oeUaalbe Underground Path Failure Common Maintenance Falls UND R OPIKOCMKlBOHYI APage 12 Both Keowee Units Underground Path Fail To Suppl Th Falls To Connect Underground PahKeowee To Omnee NOUNIT MPXHO Kaowee Unit 1 Fails The Underground To Supply The Supply Is Not Underground Power Recovered By Using Path Keowee Unit 2 Pa0e 2 Page 6 High Level Logic Model Page Page 31

Keowee Unit I Fails To Supply The Underground Power Path KU1UNDERO age 1 Pqe Keowee Unit 1 Fails Air Circuit Breaker To Stan Or Run 3 Transfers Open KUiUNDER ACB3TRANS 2

Keowee Unit 1 Fails Keowee Unit 1 Fails To Start To Run L L 1 RTO PageRU Page 32 Keowee Unit 1 Falls Keowee Ui To Start From Startup FisWe Standby The UnitHaBenG TStneratingToTeGi KUiSTATII KU1SPINNGI Keowee Unit 1 Start Keowoe Unit 1 Fails Keowee Unit 1 Is Keowee Unit 1 Fails Is Required To Start Supplying The Grid To Disconnect Or I KU1SAT M UMS ARTF l KU1RNNG]IIK1PN Pae3Page 3

Page 4 Page 3 High Level Logic Model Page2 Page 32

Keow" unk i Fails Keowee Unit I Fads Keowes Unit I start TO Start To Disconnect Of Is Required Load I.

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Modeling (cont'd)

System/Component Fault Tress Air Circuit Breakers Guide Bearing Oil Switchyard DC Power Generator Excitation Cooling Water

.0 Generator External Grid Trouble Protection System Keowee PRA Page 34

Modeling (cont'd)

System/Component Fault Tress (cont'd)

Governor Oil and Air Turbine Sump Power Paths Governor and Turbine Auxiliary AC and DC Power Keowee Start Keowee PRA Page 35

Keowee Unit 1 Generator Exciation Fails During A Cold Stan KU1GEXCLD IouI Keowee Unit I Field Keowee Unit 1 Emerge Breaker Fails To ncy Lodout Due To S Close purious Actuation Of LGen Protect Relay FLD?'XSE1 IGK19E1 Page 2 Keowee Unit I Keowee Unit 1 Gen Supply Breaker Excitation Fails To Close Transformer Is I

I Failed Page 4 Keowee Unit 1 Field Breaker 3D In 125V Flashing Breaker dc Distnibution Falls To Close Center 1 DA I

Transfers Open I FLSHCLOSE1I I ED113DCDTI Page 6 Keowee Unit 1

Field Loss Of Power To Flashing Breaker 125V dC Fails To Open Distribution Center IDA During Stan Page a Keowee Unit 1 Base Adjust Fals To Set Unit Volt-go Within The Acceptable Range Page 9 Generator Excitation Page 1 Page 36

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Results Base case analysis considers:

the current operating mode, restricted to one unit generating to the grid, operator recovery from certain unit failures.

Probability that Keowee fails to supply power to Oconee 7.05.-03 Keowee PRA Pave 38

Results (cont'd)

1)

Both Keowee Units Unavailable Due To 5.23E-03 5.23E-03 Common Maintenance

2)

A Single Keowee Unit Is Unavailable Due 1-3.80E-02 1.55E-04 To Maintenance Common Cause Failure Of Both Unit's WL 2.55E-03 Filters Due To Intake Debris Failure To Recover Flow Through Clogged 6.30E-02 Main Strainer

3)

A Single Keowee Unit Is Unavailable Due 1-3.80E-02 1.54E-04 To Maintenance Keowee Unit 1 Only Is Supplying The Grid 1-0.0 Keowee Unit 2 Only Is Supplying The Grid 1-2.44E-02 Keowee Unit 1 and 2 Are Supplying The 1-0.0 Grid Units 1 & 2 Excit Fail Due To Common 1.64E-04 1.64E-04 Cause Failure Of The Breaker Keowee PRA Paile 39

Relative Importance of the Top Ten Basic Events for Both Keowee Units Unavailable Due To Common "Oconee Emergency Power From Keowee Fails" Maintenance O A Single Keowee Unit Is Unavailable Due To Maintenance E Common Cause Failure Of Both Unit's WL Filters Due To Intake Debris U Failure To Recover Flow Through Clogged Main, Strainer l Units 1 & 2 Excit Fail Due To Common Cause Failure Of The Breakers l KHU-1 Voltage Adjust Failure Drives Generator Output Too High/Low 1 Keowee Unit 1 Generator Fault While the Unit Runs 1 Failure To Recover Keowee Auxiliary Power Breakers

• Common Cause Failure Of All Keowee Auxiliary Power Breakers Air Circuit Breaker 7 Fails To Close Due To Mechanical Failure Remainder Paoe 40,

Relative Importance of the Top Ten Basic Events for "Oconee Emergency Power From Keowee Fails" Excluding Common Cause, Maintenance and Recoveries

• KHU-1 Voltage Adjust Failure Drives Generator Output Too High/Low El Keowee Unit 1 Generator Fault While the Unit Runs B Air Circuit Breaker 7 Fails To Close Due To Mechanical Failure

• KHU-1 Base Adjust Fails To Maintain Generator Output Within Acceptable Range O1 Keowee Unit 1 Gov. Fails to Position Wicket Gates With Unit Running O Keowee Unit 1 Turbine Fails With the Unit Running E Keowee Battery No. 1 Fails During Discharge 1111 KHU-2 Voltage Adjust Failure Drives Generator Output Too High/Low

• Keowee Unit 2 Generator Fault While the Unit Runs

• ACB Air Supply Fails Causing Low Pressure In All ACB Accumulators U Remainder Page 41

Results (cont'd)

Overhead and Underground Supply Failure Probabilities Underground Power Supply 2.8E-02 Overhead Power Supply 6.6E-02 0

Note:

Common cause failures and double maintenance are not included in these results.

Keowee PRA Page 42

Results (cont'd)

Unit & Path Failure Probabilities 3

Overhead path 9.4E-OYf0 Underground path 1.1E-03 Operational unit (KU2) 1.9E-02 Standby unit (KU1) 2.5E-02 Keowee PRA Page 43

Results (cont'd)

Gate Name Result - Generic Result - Bayesian 0

Data with no credit Updated Data with no for recoveries credit for recoveries KEOWTOP 1.3E-02 1.0E-02 KU1RUN 3.OE-02 1.6E-02 KU1STARTF 1.6E-02 9.2E-03 KU2RUN 1.8E-02 1.2E-02 KU2STARTF 1.1E-02 7.8E-03 Keowee PRA Page 44

Results (cont'd)

Sensitivity Studies 1Unit 2 Units Operational Operational 7.05E-03 6.88E-03 Unrecovered 1.01E-02 9.75E-03 Keowee PRA Page 45

KEOWEE START FAILURE PROBABIUTY Experience vs. Model Prediction 0.0150 0.0100 - -Rellabilty Model Prediction (Standby Unit a

3-Yr. Ayg.(91493) a

.Relablilty Model Prediction (Gild Cycled Unit)

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0 Year Yearly Falure 3-Yr Average 3-Yr Average 3-Yr Average Rate (8547)

(88-90)

(91-93)

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RelabWy

.* Overal Relaibfty Model EMerne Model Prediction Average Prediction (Grid Cycled (Standby Unit)

DATA

SUMMARY

MA J

IM

.1M IM 12A2 1IM 1991.

IM IM 194(/4 Yearly Fallurs Rate 0.0043 0.0 0.0051 0.0 0.0046 0.0015 0.0036 0.0134 0.0068 0.0047 0.0051 3-Yr Average (85-87) 0.0017 3-Yr Average (88-90) 0.0033 3-Yr Average (91-93) 0.0064 Rellability Model Prediction (Grid Cycled Unit>

0.0077 Reliability Model Prediction (Standby Unit) 0=.092 Overall Experience Average 0.0045

0 KEOWEE 24 Hr. RUN FAILURE PROBABILITIES Reliability Model Prediction ( Standby Unit) 0.016 Reliability Model Prediction (Grid Cycled Unit) 0.012 Overall Experience (10 Year Average) 0.012

Modifications Part AL1 Deal with the single failure concern over the differential relaying zone overlap (ACB-1)

Automatically transfer the available overhead unit to the underground path Keowee PRA Page 48

Modifications (cont'd)

Part BLI Prevent connecting Keowee To Oconee when the Keowee unit is generating at too high a frequency overspeed on load rejection governor failure Open and reclose the underground breaker if that unit is generating to the grid Keowee PRA Pave 49

Modifications (cont'd)

BLI (cont'd)

ACB-3 fail to close probability,~ 8.7E-03 Applicable only when unit is generating to the grid

-6% of the time Failure contribution

~5.2E-04 Keowee PRA Page 50

Modifications (cont'd)

BL1 (cont'd)

Prevent closure of ACBs 1 through 4 if frequency is too high Prevent closure of breakers SKI and SK2 if frequency is too high, most significant new failure mode is on the order of 7.OE-06 Trip ACBs 1 through 4 if governor failure is detected Keowee PRA Page 51

Keowee PRA AC Power Reliability Results By Duncan Brewer Page 52

Outline Objectives Oconee AC Power System Overview Method Fault Tree Application of Recoveries Results 0

Keowee PRA Pave 53

Objective To Determine the Reliability of the Oconee AC Power System To Allow Importance Ranking of Keowee Systems and Components Relative to the Complete Oconee Power System To Account for the Impact of Initiating Events on the Overhead Path Keowee PRA Page 54

Oconee AC Power System Overview One Keowee Unit Aligned to Overhead Path One Keowee Unit Aligned to the Underground Path The 100 kV Path from Lee Combustion Turbine Through Central Switchyard and CT5 Transformer Any One Can Power Both Main Feeder Busses Keowee PRA Page 55

OCONEE AC POWER SYSTEM NORMAL STARTUP KEOWEE CENTRAL SOURCE SOURCE UNDERGROUND

/LEE PATH UNIT 230KV YELLOW/RED BUS GENERATOR KEOWEE OVERHEAD 13.8KV 100KV 13.8KV PATH "i

I

'L I

3T CT3 CT4 CT5 N1 N2 El E2 SK1 SK2 SL1 SL2 SBBI SBB2 4KV STANDBY BUSES Si S2 MFB1 4KV MAIN FEEDER MFB2 BUSES 4KVSGR TC TD TE Drw. PMA pg 2 (09/14/94) Rev.0

Method Started with Oconee IPE Model for AC Power System Linked with DC Power System from Oconee IPE Cut Out Old Keowee Model Linked in the New Keowee Model Combined the Keowee and Oconee Data Bases Solved the New Tree Applied Keowee and Oconee Recoveries Keowee PRA

Ocnee 4160V Mainfeeder Bus Power Fails from all Paths OPWERTOPI T5INII L

ure On Loss Te Osie Loss Of Power On Main Feeder Bus 1 Power Initiating Main Feeder Bus 2 Everit Page 2 TNIPage 313 Electrical Grid Or Station Switchyards Power Due To Severe Main Feeders Initiating Event Weather Initiating Initiating Event I

Event T5FUB EDFE 2

Initiating Event 2

Initiating Event Event Oconee-Keowee Core Damage Fault Tree C:\\CAFTA\\TREE\\OPRA\\KEON-AC1.CAF 10-10-94 Page 1 Page 58

To~ai Feeder Sum Iie Pagh I Coenrrnoo Caus 4eake El aRe"ManFmeAIMinFee AIWekrN Normi AC Pond m

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Pare 3

Page 072 Oconee-Keowee Cor Daag Faulty Tree I:CFATE\\OR\\ENC

.CF 101-9Wag

Interruption Of20 SourcFard Normal AC Power SucsFi LI ae 2

IPSTARTUP Page 3 PSWYD Page 313 230 KV Switchyard Loss Of The Oconee Oconee Emergency Failure 01 Sources Fail Station Switchyards Power Via The Electrical Grid Or IInitiating Event Overhead Path Falls Main Feeders nInitiating Event PSWYD T5SUBF Page 3 2

Iritiating Event Initiating Event Loss Of Off-Site Startup Bus Fails Oconee Emergency Both Keowee Units Keowee Fails Due To Power Due To Severe Power Via The Weather Initiating Overhead Path Fails Event M57WREAI PASRTH OVERTOP KBTHM1EWO 77ilnitiaing Event PageH9 A Single Keow60 Unit Is UnavailableToCnetKwe Due To MaintenanceToOne KU20VERO IIKK2UNITY IPTHO Keowee Unit 2 Fails Air Circuit Breaker Air Circuit Breaker Oeha ahI vredPt To Supply The 2 7Fails To Connect 2 Transfers OpenNoCmpedBrasAtrMkn Overhead Power Path Unit 2 To The Overhead Path I KU20VER l AC2LSEllACB2TRANS I-PTTP IPTTP Pagee 30 I

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Standiy Bus 1 Power Fals Pwe eerm S1 Remnains Standby Bus I Standby Bus 1 Power Standby Bus 1 Fafs open usintenance sowness Fall Unavalaly II 81 C

hu" bmCommno Cause Breake 81ndn FaI To8 rd ComponkentFa Fallure Of Breakerscos 1 DIC S

And S2 To CloseINa Module 2

ATransfer Loss Of PwrOn Loss Of Power On 125 V do Panetboard 125 V do Panelboar 3DA 3DIB Page 98 ag10 Oconee-Keowee Core Damage Fault Tree

-i C:\\CAFTA\\TREE\\OPRA\\KEON-AC1.CAF 10-10-94 T Page 102 Page 61

Standby Bus I PowerStnbBU2Poe Sources Fail Sources Fail Page 102 PSB1S P

318 PSB2S Power From Keowoe Power To Bus 1 Power From Keonee Power To Bus 2 Unit 1 To Standby Fails Given Btoth Bus 1 Fails Keowee Units in Bus 2 Fails Keoee Units In Maintenance Maintenance 1

P1 PLEE12CN Page 311 o

311 Oconee Emergency Breaker SKI Remains Omnee Breaker SK2 Remains Power Via The Open Power Via The Open Underground Path Fails Fa 0

1NO Page 108 Page toe Loss Of Power 3On4160 V ac Breaker Loss of Power On 4160 V ac Breaker 25 V dc Panelboa d

SK Fails To Close board 1 DIC 1DID D1DIC I PACXSK1C4C I D1DD I PACAK2C4C Transfer

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Transler Breaker 1 DIC-25 Breaker SK1 Closing Breaker 1DID-27 BakrSK2 Closing Transfers Open Circuit Component Trnes open CicitF ropen FailureFalr UPOCI2ASD 1 MI PACSK20MOD Module Moule Common Cause Common Cause Fallure Of Breakers Failure Of Breakers SK1 And SK2 To Close SK1 And SK2 To Close A1 PCK2COMI 2 Common Caus.

cmmon Caus.

Oconee-Keowee Core Damage Fault Tree C:\\CAFTA\\TREE\\OPRA\\KEONAC1.CAF 10-10-94 Page 107 Page 62

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Power To Bus I Power To Bus 2 Fails Given Both Fails Given Both Keowee Units In Keowee Units In Maintenance Maintenance l PLEESB1CN I I PLEESB2CN Page 107 Pae 107 Power From Lee Both Keowee Units Power From Lee Both Keowee Units Steam Station To Unavailable Due To Steam Station To Unavailable Due To Standby Bus 1 Fails Common Maintenance Standby Bus 2 Fails Common Maintenance PLEESBI 1KKlBOTHHYMI PLEESB2 l KKlBOTHHYMI

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7 Loss Of Power From 4160 V ac Standby Loss Of Power From 4160 V ac Standby CTS Breaker SL1 CT5 Breaker SL-2 Transfers Open Transfers Open rPCT Iu PAXL14 I

PCTS I PACXSL2C4TI Page 312 Pg 1

Oconee-Keowee Core Damage Fault Tree C:\\CAFTA\\TREE\\OPRA\\KEONAC1.CAF 10-10-94 Page 311 Page 64

Losst To Powe RaOM Tri ATors TripPo circugmits Fell Tanl CTSl Cir uis el Page 319 Pag 320TSPae 1

PagPae 6511

Recoveries Applied Keowee Recoveries - Only One Allowed per Cut Set Applied Oconee Recoveries Did Not Apply Offsite Power Recovery Keowee PRA Page 66

Results Three Loss of Offsite Power Initiating Events are Modeled Loss of the Grid (T5FEEDF) = 2.73E-2 / YR Loss of the Switchyard (T5SUBF) =

4.86E-2 / YR Weather Related LOOP (T5WEATH) = 1.44E-2

/YR Frequency of Loss of all AC Power to the Main Feeder Buses = 5.8E-5 / YR Keowee PRA Page 67

Initiating Event Contribution to Loss of Power to Oconee Main Feeder Busses (Frequency=5.8E-5/yr)

Loss of 230 kV Switchyard Loss of Grid Power 7%

5%

Weather Causes Loss of Offsite Power 88%

Page 68

Basic Event Contribution to Loss of Power to Oconee Main Feeder Busses (Frequency=5.8E-5/yr)

Operators Fail to Swap Failure of the 100 kV Uni to Underground Overhead Lines Transformer CT4 is in Maintenance Keowee Unit 2 in Maintenance Both Keowee Units in Maintenance Page 69

Keowee PRA AC Power - Core Melt Frequency Results By Duncan Brewer

• 17

Outline Objectives Overview Method Fault Tree Application of Recoveries Results Keowee PRA Page71

Objectives To Determine the Oconee Core Damage Frequency for Sequences Involving Keowee To Allow Importance Ranking of Keowee Systems and Components Relative to the Contribution to Core Damage To Compare to the "Black Box" Representation of Keowee in the Oconee IPE Submittal Keowee PRA PaNe72

ONS Core Damage Model Overview Core Damage Sequences Involving Keowee that Result from a LOOP Initiating Event Take Two Forms:

RCP Seal LOCA without Primary System Makeup Capability Failure of SSHR without the Ability to Perform Feed and Bleed Cooling Keowee PRA Page 73

ONS Core Damage Model Overview The "RCP Seal LOCA without Primary System Makeup Capability" Sequence Requires the Following Failures:

All AC Power ( HPI Cooling to the RCP Seals)

SSF Fails to Provide RCP Seal Cooling Keowee PRA Page 74

ONS Core Damage Model Overview The "Failure of SSHR without the Ability to Perform Feed and Bleed Cooling" Sequence Requires the Following Failures:

All AC Power (Fails the Motor Driven Em.

Feedwater Pumps and HPI Cooling)

Failure of the Turbine Driven Em. Feedwater Pump Failure of the SSF Aux. Service Water Pump Keowee PRA Nee' 75

OUENCHLP-46 LP-45

&JS SPRAY VENT AT ASCU DISCH4ARGE DISCHRGE PCC-lOB PRSUIE VENT AT RSCU DISCARGE Em(R.

FOB ac-Iss 941A LIE COE FOODCORE FLOWO SPTAW A

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• Pagec76,

Method Started with Oconee IPE Model for AC Power System Linked with the ONS DC Power System Model, the ONS Emergency Feedwater Model, and SSF Model from Oconee IPE Cut Out Old Keowee Model Linked in the New Keowee Model Combined the Keowee and Oconee Data Bases Solved the New Tree Applied Keowee and Oconee Recoveries Keowee PRA Page 77

Core Damage Event Occurs as the Result of Loss of Offsite Power OCDFTOP Failure Of Failure Of Reactor Secondary Side Heat Coolant Pump Seal Removal Cooling SGSSHR RCPSEAL Oconee 4160V Failure Of SSF ASW Total Loss Of Oconee 4160V Failure Of SSF RCM Mainfeeder Bus (Independent Of Emergency Feedwater Mainfeeder Bus (Independent Of Power Fails from RCM) Without Plant Power F srom AS WtA it Plant 01 Paths

~~~Power AvailablealPthPoeAvibe IOPERTO NSFSSFOREC F1 IOPWERTOPI NSFSSF6REC Page 2 Recovery /Module Pae 2 Recovery / Module Independent Failures Upper Surge Tanks Of EFW Flow To Both Are Not Available Steamn Generators Page 322 Page 351 Oconee-Keowee Core Damage Fault Tree C:\\CAFTA\\TREE\\OPRA\\KEON-CD1.CAF 10-10-94 Page 1 Page 78

Oconee 4160V Mainfeeder Bus Power Fails from all Paths Page IOPWERTOPI Page 1 Page 1 Loss Of Power On Loss of Offsie Loss Of Power On Main Feeder Bus I Power Initiating Main Feeder Bus 2 Event PMFB1 T5INIT PMFB2 Page 3 age 314 Failure 01 Loss Of The Oornee Loss Of Off-Site Electrical Grid Or j

Station Switchyards Power Due To Severe Main Feeders Initiating Event Weather Initiating Initiating Event Event T5FEQ I

SUFITWEATH I

Initiating Event nitiating Event Initiating Event Oconee-Keowee Core Damage Fault Tree C:\\CAFTA\\TREE\\OPRA\\KEON-CD1.CAF 10-10-94 Page 2 Page 79

Recoveries Applied Keowee Recoveries - Only One Allowed per Cut Set Applied Oconee Recoveries Applied Offsite Power Recoveries Keowee PRA Page 80 a

Results Frequency of Core Damage Resulting From Loss of Offsite Power = 1.O1E-6 / YR This is Comparable to the Oconee IPE Results of 3.2E-6 I YR (Higher Maintenance and Common Cause Values in IPE Study)

Keowee PRA Page 81

NRCKEOl.XLS Chart 3 Basic Event Contribution to Loss of Power Core Damage Sequences (Frequency= 1.01 E-6/yr)

SSF Diesel Generator Fails to Run SSF Diesel Generator in Maintenance Transformer CT4 is in Maintenance Both Keowee Units in Maintenance S

Operators Fail to Start SSF RCMP Page c2