ML022310392
| ML022310392 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 07/25/2002 |
| From: | Greenlee S, Joseph E Pollock American Electric Power Co |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| EA-01-286 | |
| Download: ML022310392 (37) | |
Text
N Donald C.Cook Nuclear Plant Regulatory Conference Essential Service Water Debris Intrusion Event July 25, 2002 Slide 1 Z wLEN POWFR
Opening Remarks Joe Pollock Site Vice President
'"IFRMI-Slide 2 =EECM POVJ
Agenda
- Opening Remarks Joe Pollock
- Presentation Overview Scot Greenlee
- Event Overview Gordon Arent
- Significance Determination Pam Cowan /
- Updated AEP Analysis Pam Cowan /
Jack Giessner S Summary Scot Greenlee Closing Remarks Joe Pollock Slide 3 zOW=
PresentationOverview Scot Greenlee Director Nuclear Technical Services Slide 4 Z ELwMI PomWER
PresentationOverview
- Event Sequence and Corrective Actions
- New Information and Considerations for NRC Significance Determination
- Updated AEP Risk Case - Confirmed by Third Party Expert Reviews Slide 5 AMSGo
or Event Overview Gordon Arent Manager Regulatory Affairs Slide 6 =AMERWM*
PI Screenhouse Layout Diagram 0' 0 N A Slide 7 -
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Essential Service Water Supply Slide 8 Z: AMER WAN PELESIC PowER
r rEvent Overview
- August 29, 2001
- Unit 1 cooling down for forced outage maintenance
- Unit 2 at 100% power
- Unit 1 Circulating Water (CW) System Removed From Service
- Cross-flow patterns created
- Forebay debris transported into essential service water (ESW) pump bay
- Damaged ESW Strainer Provides Bypass Pathway Slide 9 Z W
Event Overview
- ESW Debris Intrusion Occurs
- Plant Alignment Transports Debris to Emergency Diesel Generator (EDG) Coolers
- Debris Causes Reduced ESW Flow
- Operators Detect Reduced ESW Flo. -
- Declare EDGs inoperable and take action to restore flow
Removed From Service; Slake 10 '4-iMMELEMTIC M!OWER.
POWER
X Event Causal Factors
- Root Cause
- Damaged ESW pump discharge strainer caused by weaknesses in maintenance practices and procedures
- Contributing Causes
- Two CW pump discharge valves remained partially open
- EDG coolers could be fed from either ESW train (original plant design basis)
- Center intake isolation valve (WMO-30) approximately 5%
open (increases debris availability)
- Recent biocide treatment (increases debris availability)
Slide 11 ! ELucMIC POWW
CorrectiveAction Summary
- Inspected and Replaced ESW Strainer Baskets
- Revised ESW Strainer Maintenance Procedures
- Enhanced Monitoring of ESW System Performance
- Initiated CW Pump Discharge Valve Refurbishment
- Inspected, Cleaned, and/or Flushed Susceptible Heat Exchangers and Piping Slide 12 ZELECTIC POMFE
CorrectiveAction Summary
- Verified Adequate ESW Flow to System Components
- Alternate supply valves normal operating configat-ioinlose4;- le -
- Design change eliminated automatic opening following an EDG automatic start CorrectiveActions Effective Slide 13 \ km PWMERA-EUWMX2R POWER
Significance Determination Pam Cowan System Engineering Manager Jack Giessner Event Recovery Manager Slide 14 E.WERW
Significance Determination -
- kIntroduction/ Outline
- Background Information and Preliminary Finding Significance
- New Information and Considerations For Significance Determination
- Discussion of information
- PSA determination results
- Conservatisms in approach Slide 15 =ELKMJC
Significance Determination
- Background
- Event Significance Based on Loss of Offsite Power (LOOP) With Possible Debris Intrusion and EDG Failure
- Dual and Single Unit LOOP Events Considered
- Single Unit LOOP Debris Transport Similar to August 29, 2001 Event
- Dual Unit LOOP Debris Transport Caused by Forebay Transient (Refill) When Circulating Water Pumps Trip
Significance Determination -
Background
Unit l f I2ESWheader
_and iiG colIs _ 91 Cooling flow Unsucc~essful In P degradation Impacts performing-UnIit2 flow 2Cd6E~dGfnction r~estorain oivte Slide 17 SliIdeR7N OEWRIC
Significance Determination -
Preliminary
- NRC Review Identified Changes in Probability Factors Used by AEP Event AEP NRC Block 1: LOOP occurs 1 1 Block 2: Sufficient suspended debris is present 0.0189 0.5 Block 3: Suspended debris reaches ESW pump suctions 0.99 1 Block 4: 1E ESW damaged strainer basket is in service 0.7708 0.77 Block 5A: Flow through 1E ESW strainer is "low" 0.851 0 Block 5B: Flow through 1E ESW strainer is "high" 0.149 1 Block 6A: Ingested debris bypasses 1E ESW strainer 0.1 ---
Block 6B: Ingested debris bypasses 1E ESW strainer 0.95 1 Condition: Bypassed debris enters Unit 1 EDG coolers 1 1 Block 7: Bypassed debris reaches Unit 2 EDG coolers 0.25 0.25 Block 8: Cooling flow degradation impacts EDG function 0.25 0.707 (Note 1)
Block 9: Condition is not identified/cleared by operators 0.13 0.36 (Note 2)
Note 1 - Block 8 value is a combined probability of 0.25 for failure of all four EDGs, which gives an individual EDG failure probability of V6I2 = 0.707 Note 2 - Block 9 value when applied on a per plant basis results in a probability of V-B = 0.36 Slide 18 POWER
Significance Determination
- k Preliminary
- EDG common cause failure factor (CCFF) developed using revised probabilities from AEP model
- CCFF used to obtain change in core damage frequency (A CDF) from SPAR model -1.8E-05/year (Yellow)
- Change in large early release frequency (A LERF) determined by using 0.4 conditional containment failure probability 7.1 E-06/year (Yellow)
Slide 19 ;EUC POW=R
New Information IConsiderations Slide 20 POWER
Significance Determination -
New Information / Considerations
- EDG Failure Probability Discussions Will Focus on Highlighted Areas Event AEP NRC Block 1: LOOP occurs 1 1 Block 2: Suf icienM sus d sp ^ K^O189.
Block 3: Suspended debris reaches ESW pump suctions 0.99 1 Block 4: 1E ESW damaged strainer basket is in service 0.7708 0.77 Block 5A: Flow through 1E ESW strainer is "loW' 0.851 0 Block 5B: Flow through 1E ESW strainer is "high" 0.149 1 Block 6A: Ingested debris bypasses 1E ESW strainer 0.1 Block 6B: Ingested debris bypasses 1E ESW strainer 0.95 1 Condition: Bypassed debris enters Unit 1 EDG coolers 1 1 Block 7: Bypassed debris reaches Unit 2 EDG coolers 0.25 0.25 Block 8: Cooling flow degradation impacts EDG function 0.25 0.707 (Note 1)I Note 1 - Block 8 value is a combined probability of 0.25 for failure of all four EDGs, which gives an individual EDG failure probability of ~ 0.25 = 0.707 Note 2 - Block 9 value when applied on a per plant basis results in a probability of V0IB = 0.36 Slide 21 ZAMERECAN'
.ELECTRIC POWE
New Information -
- Block 2
- Additional Information Developed to Better Assess Probability Estimate
- Hydraulic Model Developed
- Model Benchmarked Against 1977 Screenhouse Forebay Level Response Test
- Upward Velocities May Exist up to 135 Seconds Following Trip of CW Pumps
- Screenhouse Water Level Maximized and Velocities Are Zero at 135 Seconds
- Forebay Level Oscillates Until Consistent With Lake Slide 22 =ELUIPRC
New Information -
Block 2 Post Dual-Unit LOOP Screenhouse Vertical Velocity
- Hydraulic Model Used to Develop Vertical Velocity Data
- Maximum Upward Bulk 0 (D
Velocity 0.20 fps co I-
- Maximum Oscillation Bulk Velocity 0.04 fps
- 3X Multiplier for Localized Velocities 0 20 40 60 80 100 120 140 160 Seconds 3ANIERICAN 9T ZEII1RC Slide 23 o Me
New Information
- ~Block 2 Debris Lift Following Dual-Unit LOOP
- Terminal Settling Velocities 16.0 " 1 Recalculated 14.0
- 0.3 fps for sand 12.0 SandD - 0.5 fps for mussels 10.0 aa)
LL - Calculations Correlated to Field 6.0 Demonstration 2.0 Mussel
- Debris Lift Determined From 00 20 60 SIp 100 120 140 160 Water and Settling Velocities seconds Assuming a sustained peak velocity of 3 times the bulk average velocity in the area of the ESW pumps.
Slide 24 WLECI POWER
New Information Block 2
- ESW pump vulnerability is about 40 seconds
- Mussel shells rise approximately 2 feet and fall to the floor in approximately 70 seconds
- ESW pumps sequence on EDGs at TO+30 seconds
- Other Block 2 Sub-blocks Adjusted to Reflect Revised Subjective Probability Scale 4-14,
- Overall Probability That Suspended Debris is Sufficient to Challenge ESW is 0.04 Screenhouse Refill Not a Credible Challenge to,the Planto I MAERJCAN Slide 25 ELECIC POWE
New Information Block 9
- Human Error Probability (HEP) Values Developed for Each Unit
- Unit Control Rooms Act Independently and Are Physically Separated HEP Value Intendbed Fbr Application on a UnMit Basis -..
Slide 26 I I ERIC POWS&,
Significance Determination -
- New Information I Considerations
- Additional Considerations
- LERF
,, Approach consistent with RG 1.174
>>AEP model used in prior docketed AEP correspondence to NRC
- AEP PSA Model
>> WinNUPRA widely used and accepted
>> Peer certification process
>>Supports maintenance rule decision-making
>> Basis for previously docketed AEP correspondence to NRC Siide 27 ZELEWRIC POWER
Significance Determination -
New Information I Considerations
- PSA Results of Dual Unit LOOP With Station Black Out - Using New Information / Considerations A CDF 3E-8 /year (Green)
Slide 28 PORER
Significance Determination
- k New Information/ Considerations
- Conservative Assumptions in This Approach:
- The following blocks were not modified, but AEP analysis shows conservatism
>> Block 5A: Flow through 1E ESW strainer is "low"
>> Block 5B: Flow through 1E ESW strainer is "high"
>> Block 6A: Ingested debris bypasses 1E ESW strainer
>> Block 8: Cooling flow degradation impacts EDG function
- Technical specification required charging system cross-tie not modeled
- Technical specification required 69 KV offsite power source not credited Slide 29 Z: WDVE POWER
Updated AEP Evaluation Pam Cowan System Engineering Manager Jack Giessner Event Recovery Manager Slide 30 LAMPUER
=EIECUME
Updated AEP Evaluation
- Original Probabilistic Study Developed April 2002
- Used as input to NRC evaluations
- Revised July 2002 based on new information and expert reviews
- EDG Failure Probability Inputs Revised (Highlighted)
Event Original Revised Block 1: LOOP occurs 1 1 Block 2: Sufficient suspended debris is present 0.0189 0.04 Block 3: Suspended debris reaches ESW pump suctions 0.99 0.99 Block 4: 1E ESW damaged strainer basket is in service 0.7708 2 O=7 tO":
Block 5A: Flow through 1 E ESW strainer is "lowv' 0.851 0.85 Block 5B: Flow through 1E ESW strainer is "high" 0.149 0.15 Block 6A: Ingested debris bypasses 1E ESW strainer 0.1 0.3 Block 6B: Ingested debris bypasses 1E ESW strainer 0.95 1 Condition: Bypassed debris enters Unit 1 EDG coolers 1 1 Block 7: Bypassed debris reaches Unit 2 EDG coolers 0.25 0.25 Block 8: Cooling flow degradation impacts EDG function 0.25 0.5 Block 9: Condition is not identified/cleared by operators 0.13 0.13 Slide 31 ZAMERICAN' ELECTRIC POWER
Updated AEP Evaluation
- Single Unit LOOP Scenarios Eliminated
- Additional time (hours) to develop contingency strategies
- Ability to cross-connect charging from other Unit
- Use of 69 KV offsite power
>> physically separated from main switchyard
- Most Limiting A LERF Value Used:
- .2 conditional containment failure probability factor, or
- AEP model Slide 32 AMERWM*
POWER
p.
Updated AEP Evaluation
- Results of Updated AEP Evaluation:
Unit 1 Unit 2 A CDF 6.1 E-7 (Green) 4E-8 (Green)
A LERF 1.2E-7 (White) 9E-9 (Green)
Slide 33 '"IF0air'"O PWS
Updated AEP Evaluation
- Conservatisms
- Technical specification required charging system cross tie not credited
- Technical specification required 69 KV offsite power source not considered
- Most limiting A LERF value used:
>> .2 conditional containment failure probability factor, or
>> AEP model Slide 34 G ELWRRC PWER
Summary Scot Greenlee Director Nuclear Technical Services Slide 35 G WMMU POWEm
Summary
- Third Party Reviews Show Results Are Sound
- Modified Approaches Produced Similar Results
- Conservatism (Over-Estimation of Risk) Exists in Either Approach Considern Conservatisms1 AEP Overall EventRisk Significance Conclusion is: "GREEN" Z: AElR"CA Slide 36
, , ".A_ M o,I i, I I
Closing Remarks Joe Pollock Site Vice President Slide 37 0AMEJUCAN
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