ML022310392

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Regulatory Conference Slides
ML022310392
Person / Time
Site: Cook  American Electric Power icon.png
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)
v • d • e


Text

{{#Wiki_filter: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 Slide 2 '"IFRMI- =EECM POVJ

Agenda

  • Opening Remarks
  • Presentation Overview
  • Event Overview
  • Significance Determination Joe Pollock Scot Greenlee Gordon Arent Pam Cowan /

Jack Giessner Pam Cowan / Jack Giessner Scot Greenlee Joe Pollock zOW=

  • Updated AEP Analysis S

Slide Summary Closing Remarks 3

Presentation Overview Scot Greenlee Director Nuclear Technical Services Slide 4 Z ELwMI PomWER

Presentation Overview

  • 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 An.. E&MEKI% POw-M

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

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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

  • EDGs Returned to Operable Status Unit 2 Conservatively Removed From Service;

'4-M!OWER. iMMELEMTIC POWER Slake 10

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

Corrective Action 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

Corrective Action Summary

  • Verified Adequate ESW Flow to System Components
  • Revised Operation of Alternate ESW Supply to the EDG Coolers Alternate supply valves normal operating configat-ioinlose4;- le -

Design change eliminated automatic opening following an EDG automatic start Corrective Actions Effective PWMERA-km EUWMX2R POWER Slide 1 3 \\

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

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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
  • Model Developed by AEP to Evaluate EDG Failure Probability Given a LOOP Slide 16

=ELWIC PCKER

Significance Determination -

Background

Unit I2ESWheader l f _and iiG colIs 91 Cooling flow Unsucc~essful In P degradation Impacts performing-UnIit2 flow 2Cd6E~dGfnction r~estorain oivte Slide 17 SliIdeR7 N 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: 1 E ESW damaged strainer basket is in service 0.7708 0.77 Block 5A: Flow through 1 E ESW strainer is "low" 0.851 0 Block 5B: Flow through 1E ESW strainer is "high" 0.149 1 Block 6A: Ingested debris bypasses 1 E ESW strainer 0.1 Block 6B: Ingested debris bypasses 1 E 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 probability of V6I2 = 0.707 an individual EDG failure 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
  • NRC Determined Dominant Risk Sequence to be Dual Unit LOOP Followed by the Failure of All EDGs 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

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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 s p ^ K^O189. Block 3: Suspended debris reaches ESW pump suctions 0.99 1 Block 4: 1 E ESW damaged strainer basket is in service 0.7708 0.77 Block 5A: Flow through 1 E ESW strainer is "loW' 0.851 0 Block 5B: Flow through 1 E ESW strainer is "high" 0.149 1 Block 6A: Ingested debris bypasses 1 E ESW strainer 0.1 Block 6B: Ingested debris bypasses 1 E 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

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New Information Block 2

  • Hydraulic Model Used to Develop Vertical Velocity Data Post Dual-Unit LOOP Screenhouse Vertical Velocity
  • Maximum Upward Bulk Velocity 0.20 fps 0(D co I-
  • Maximum Oscillation Bulk Velocity 0.04 fps
  • 3X Multiplier for Localized Velocities 0

20 40 60 80 Seconds 100 120 140 160 Slide 23 3ANIERICAN ZEII1RC 9T 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 WLECIM 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 MAERJCAN ELECIC POWE Slide 25 I

New Information Block 9

  • Human Error Probability (HEP) Values Developed for Each Unit
  • Unit Control Rooms Act Independently and Physically Separated Are HEP Value Intendbed Fbr Application on a UnMit Basis ERIC POWS&,

Slide 26 I I

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 ide 27 ZELEWRIC POWER Si

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)

A LERF 7E-9/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 1 E ESW strainer is "low" >> Block 5B: Flow through 1 E ESW strainer is "high" >> Block 6A: Ingested debris bypasses 1 E 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: 1 E 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 1 E 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:

A CDF A LERF Unit 1 6.1 E-7 (Green) 1.2E-7 (White) Unit 2 4E-8 (Green) 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 Either Approach in Considern Conservatisms1 AEP Overall EventRisk Significance Conclusion is: "GREEN" Z:

AElR"CA Slide 36 , _ M o i, I ".A ,I I

Closing Remarks Joe Pollock Site Vice President Slide 37 0AMEJUCAN =ELiWR§}}

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