ML20112F404

Final ASP Analysis - Columbia (LER 397-02-001)

ML20112F404
Person / Time
Site:	Columbia
Issue date:	02/14/2002
From:	Christopher Hunter NRC/RES/DRA/PRB
To:
Hunter C (301) 415-1394
References
LER No. 397/02-001
Download: ML20112F404 (18)

Text

SENSITIVE - NOT FOR PUBLIC DISCLOSURE SENSITIVE - NOT FOR PUBLIC DISCLOSURE 1

Final Precursor Analysis Accident Sequence Precursor Program --- Office of Nuclear Regulatory Research May 17, 2004 Columbia Generating Station Unreliable Breakers for Four Safety-Related Systems Event Date: 02/14/2002 LER: 397/02-001 397/2002-001-00 CDP = 6x10-6 Operating Condition Summary Description. On February 13, 2002, the plant was in Mode 1 at 100% of rated thermal power.

During a planned online maintenance of the Emergency Diesel Generator (EDG)-2 at Columbia Generating Station (CGS), the plant operators attempted to close the EDG-2 output breaker.

But, the breaker failed to close because the Mechanism-operated Cell (MOC) switch assembly in the breaker failed to change state on demand. Then, operators decided to shutdown the plant due to LCO requirements of TS 3.8.1, Action B.4. (Reference 1)

In calendar year 2002, first quarter, Region IV conducted a special inspection for MOC switch assemblies for breakers of safety-related systems (EDG, Standby Service Water (SSW) system, Low Pressure Core Spray (LPCS) system, Residual Heat Removal (RHR) system).

Region IV documented their non-compliance findings and unreliability findings for breakers (References 2, 3, and 4). These findings were:

1. On June 29, 2001, the licensee completed design modification (new replacement breakers) for Division II SSW system. But the design control measures established by the licensee were not adequate to assure the suitability of the replacement breakers. Specifically, the licensee failed to incorporate vendor information regarding maintenance of MOC switches in these breakers. On November 19, 2001, the same Division II SSW system breaker MOC switch failed to close on demand a second time.

2. The licensee failed to identify the cause of the same condition and take corrective actions to preclude recurrence of MOC switch close-failures for other safety-related systems (EDGs, the LPCS system, and the RHR system) for which replacement breakers were installed previously.

So, on February 14, 2002, a similar close-failure occurred involving the MOC switch associated with the Division II EDG breaker.

3. The licensee experienced 4 breaker MOC switch failures between June 29, 2001 and February 14, 2002. The failures were due to inadequate breaker maintenance combined with the marginal capability of a new breaker design. Four MOC switch failures occurred in 2 of the 4 safety-related systems (SSW and EDG).

LER 397/02-001 SENSITIVE - NOT FOR PUBLIC DISCLOSURE 1 Since this condition did not involve an actual initiating event, the parameter of interest is the measure of the incremental change between the conditional probability for the period in which the condition existed and the nominal probability for the same period but with the condition nonexistent and plant equipment available. This incremental change or importance is determined by subtracting the CDP from the CCDP. This measure is used to assess the risk significance of hardware unavailabilities especially for those operating conditions where the nominal CDP is high with respect to the incremental change of the conditional probability caused by the hardware unavailability.

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4. The replacement breakers installed by the licensee for the above 4 safety-related systems did not render all safety-related pumps inoperable at the same time. Rather, it increased the probability of breaker failure-to-close on demand during the operating condition (Reference 2).

Cause. CGS system engineers determined that the failure of the MOC switches to not fully actuate was due to lack of preventive maintenance and a breaker replacement that produced less drive force to actuate the MOC assembly on close-demand. The root cause was the failure to recognize the importance of MOC assembly preventive maintenance.

Condition duration. The operating condition involving unreliable breaker MOC switches for 4 safety-related systems existed for 5216 hours0.0604 days <br />1.449 hours <br />0.00862 weeks <br />0.00198 months <br /> (between 6/29/2001 and 2/14/2002).

Related events. None.

Recovery opportunity. During testing of replacement breakers, the licensee locally recovered 50% of the MOC switch close-failures (two successful recoveries out of four failures). A non-recoverable failure probability of 0.5 is applied to the increased probability of failure-to-close on demand for replacement breakers.

Analysis Results Importance1 The risk significance of inoperable breakers for four safety-related systems for a condition duration of 5216 hours0.0604 days <br />1.449 hours <br />0.00862 weeks <br />0.00198 months <br /> was determined by subtracting the nominal core damage probability (point estimate) from the conditional core damage probability (point estimate):

Conditional core damage probability (CCDP) =

1.19E-5 Nominal core damage probability (CDP) =

5.7E-6 Importance (CDP = CCDP - CDP) =

6.2E-6 The estimated importance (CCDP-CDP) for the operating condition was 6.2E-6.

An uncertainty analysis was conducted for the operating condition. The mean estimates for CCDP, CDP, and importance were 1.230E-5, 6.165E-6, and 6.134E-6 respectively, as shown in Table 5.

Dominant sequence Loss of offsite power involving successful operation of at least one of two emergency diesel generators followed by successful cycling of the safety relief valves and the High

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Pressure Core Spray system, but failure of containment heat removal function (failure of suppression pool cooling, shutdown cooling, and containment spray) due to RHR system failures, and failure of containment venting [Sequence 05]. Importance for this dominant sequence is = 1.9E-6. The events and important component failures in this sequence are as follows:

- Loss of offsite power-initiating event

- Successful reactor shutdown

- Successful start and run of two emergency diesel generators

- Successful cycling of safety relief valves

- Successful operation of the High Pressure Core Spray system

- Successful manual depressurization

- Failure of suppression pool cooling mode, shutdown cooling mode, and containment spray mode of the RHR system and the SSW system due to unreliable pump breakers

- Failure of containment venting

- Onset of potential core damage Path for dominant sequence LOOP 05 is shown in Figure 1.

Results tables Table 1 provides the conditional probabilities for the dominant sequences.

Table 2a provides the event tree sequence logic for the dominant sequences listed in Table 1.

Table 2b provides the definitions of fault trees used in event tree logic listed in Table 2a.

Table 3 provides the conditional (CCDP) cut sets for the dominant sequences.

Table 4 provides the definitions and probabilities for added basic events and condition-affected basis events and frequencies for initiating events.

Modeling Assumptions Assessment summary Assessment type - The breaker failures were for those installed in the plant and failed during actual surveillance test demands. Of the four breaker failures, two were intermittent and were recovered. It is also noted that the licensee corrected the MOC switch assembly problems on 2/14/2003. Therefore, the operating condition for the unreliable breakers was assessed using a condition assessment for a plant condition in which the plant was operated with replacement breakers with high probability of failures.

The operating condition was assessed for a period of 5216 hours0.0604 days <br />1.449 hours <br />0.00862 weeks <br />0.00198 months <br /> (between 6/29/2001 and 2/14/2002).

Operating experience for breakers-Based on licensee-provided information for these breakers in four safety-related systems, 4 failures in 103 test demands were observed and documented, with 2 of the 4 failures recovered (intermittent). A BETA distribution was assigned to characterize test-based failure probabilities using Reference 6 with a mean value

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= (4/103)*(2/4) = 1.9E-2; and Parameters a = 4.5; b = 103 - a = 98.5.

Model use - The Revision 3i Standardized Plant Analysis Risk (SPAR) model for Columbia Generating Station (formerly known as Washington Nuclear Plant) Unit 2 (Reference 5) was used for this assessment.

Model update to Revision 3i SPAR model - 8 basic events to represent the MOC switch-induced failures (EDG output breaker failure to close on demand, and pump breaker failure to close on demand) were added to four system fault trees (EDG, SSW, LPCS and RHR). Modified fault trees are shown in Figures 2 thru 9. Probability for these basic events in the base case was set to FALSE. Probability for these basic events in the current case (condition case) was set to 1.9E-2.

Basic event probability changes Table 4 provides the basic events that were added and modified to reflect the operating condition being analyzed. Revision 3i SPAR plant model did not model output breakers for EDGs and breakers for pumps of the four safety-related systems (EDG, SSW, RHR, LCS). If the fail-to-close failure mode of a breaker would occur, then the EDG power supply to the safety-related buses would fail, and the pumps would not start. Therefore, a basic event that would represent the fail-to-close failure mode of the affected breakers for each of the four safety-related system (a total of eight basic events) was added as part of the fault tree update for the above four systems. Each of the basic events was set to FALSE in the base case. A mean failure probability of 1.9E-2 with a BETA distribution (a

= 4.5 and b = 98.5) was assigned in the condition assessment (current case) based on operating failures and recovery data for breakers. The basic events that were added to the base model are shown in Table 4.

Uncertainty analysis and range for total importance due to operating condition Uncertainty analysis of the operating condition along with parameters was performed using the SAPHIRE code. Default distribution types for applicable initiating events (e.g.

single unit loss of offsite power, transients) and basic events for components were documented in the Revision 3i SPAR model for CGS. These uncertainty values and uncertainty values for condition-affected basic events (eight basic events) were used in estimating mean condition-CDP values and mean condition-CCDP values. Other statistical values such as point values, median values, 5% values, and 95% values were also estimated for CDP and CCDP analysis cases. Estimated statistical values for the operating condition are shown in Table 5.

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References 1.

Energy North west, LER 397-2002-001-00, Completion of Technical Specification required shutdown to comply with Technical Specification LCO 3.8.1 Required Action of Condition F dated April 10, 2002. (ADAMS ACCESSION No. ML021130475) 2.

USNRC, Region IV, NRC SPECIAL INSPECTION TEAM REPORT FOR COLUMBIA GENERATING STATION 397/02-05 dated May 22, 2002. (ADAMS ACCESSION)

No. ML021430088 3.

USNRC Office of Enforcement, FINAL SIGNIFICANCE DETERMINATION FOR A WHITE FINDING AND NOTICE OF VIOLATION (NRC INSPECTION REPORT NO.

50-39702-05) (COLUMBIA GENERATING STATION) - EA-02-107 dated June 24, 2002.

(ADAMS ACCESSION No. ML021750255) 4.

USNRC, Region IV, COLUMBIA GENERATING STATION - NRC SUPPLEMENTAL AND BASELINE INSPECTION REPORT 50-397/02-06 dated January 23, 2003. (ADAMS ACCESSION No. ML030230794) 5.

Richard E. Gregg, Revision 3i Standardized Plant Analysis Risk (SPAR) Model for Washington Nuclear Plant Unit 2 (ASP PWR C) by Idaho National Engineering and Environmental Laboratory, May 2000.

6.

M. Englehardt, et. Al,, Handbook of Parameter Estimation for Probabilistic Risk Assessment, NUREG/CR-6823, SAND2003-3348P, Sandia National Laboratories, Albuquerque, NM, September 2003.

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Table 1. Conditional probabilities (point values) for the dominant sequences Event tree name Sequence no.

Conditional core damage probability (CCDP)

Core damage probability (CDP)

Importance (CCDP - CDP)2 LOOP 05 2.8E-6 9.1E-7 1.9E-6 LOOP 36-16 1.4E-6 1.2E-6 2.0E-7 Total (all sequences)1 1.2E-5 5.7E-6 6.2E-6 Notes:

1.

Total CCDP and CDP includes all sequences (including those not shown in this table).

2.

Importance is calculated using the total CCDP and total CDP from all sequences of all applicable event trees. Sequence level importance measures are not additive.

Table 2a. Event tree sequence logic for dominant sequences Event tree name Sequence No.

Logic

(/ denotes success; see Table 2b for top event names)

LOOP 05

(/RPS)*(/EPS)*(/SRV)*(/HCS)*(SPC)*(/DEP)*

(SDC)*CSS)*(CVS)

LOOP 36-16

(/RPS)*(EPS)*(B1)*(P1)

Table 2b. Definitions of fault trees used in event tree logic listed in Table 2a SRV SRVs FAIL TO CLOSE EPS EMERGENCY POWER FROM 2 EDGs IS UNAVAILABLE RPS REACTOR SHUTDOWN FAILS HCS HPCS FAILS TO PROVIDE SUFFICIENT FLOW TO REACTOR VESSEL SPC SUPPRESSION POOL COOLING MODE OF RHR FAILS DEP MANUAL DEPRESSURIZATION FAILS SDC SHUTDOWN COOLING MODE OF RHR FAILS CSS CONTAINMENT SPRAY MODE OF RHR FAILS CVS CONTAIMENT VENTING FAILS B1 DIVISION III POWER IS UNAVAILABLE P1 ONE SRV FAILS TO CLOSE

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Table 3a. CCDP cut sets for LOOP Sequence 05 CCDP Percent contribution Minimal cut sets1 Event Tree: LOOP, Sequence 05 2.245E-7 8.1 EPS-DGN-TM-DG2

• OEP-XHE-NOREC-12H * /SRV

• RHR-MDP-MOC-1A 2.245E-7 8.1 EPS-DGN-TM-DG2

• OEP-XHE-NOREC-12H * /SRV

• SSW-MDP-MOC-1A 2.8E-006 Total2 Table 3b. CCDP cut sets for LOOP Sequence 36-16 CCDP Percent contribution Minimal cut sets1 Event Tree: LOOP, Sequence 36-16 5.738E-7 43.4 EPS-DGN-CF-RUN

• PPR-SRV-OO-1VLV 7.302E-8 28.3 EPS-DGN-CF-START

• PPR-SRV-OO-1VLV 1.4E-006 Total2 1.

See Table 4 for definitions and probabilities for the basic events.

2.

Total CCDP includes all cut sets (including those not shown in this table).

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Table 4 - Definitions and probabilities for modified and dominant basic events Basic event name Description Added to Probabi.

Modified Note Base model to reflect condition EPS-DGN-MOC-1A EDG 1A BREAKER FAILS TO CLOSE YES 1.9E-2 YES 1

EPS-DGN-MOC-1B EDG 1B BREAKER FAILS TO CLOSE YES 1.9E-2 YES 1

RHR-MDP-MOC-1A RHR MDP 1A BREAKER FAILS TO CLOSE YES 1.9E-2 YES 1

RHR-MDP-MOC-1B RHR MDP 1B BREAKER FAILS TO CLOSE YES 1.9E-2 YES 1

RHR-MDP-MOC-1C RHR MDP 1C BREAKER FAILS TO CLOSE YES 1.9E-2 YES 1

SWS-MDP-MOC-1A SWS MDP 1A BREAKER FAILS TO CLOSE YES 1.9E-2 YES 1

SWS-MDP-MOC-1B SWS MDP 1B BREAKER FAILS TO CLOSE YES 1.9E-2 YES 1

LCS-MDP-MOC-P1 LCS MDP P1 BREAKER FAILS TO CLOSE YES 1.9E-2 YES 1

OEP-XHE-NOREC-12H OPERATOR FAILS TO RECOVER AC POWER IN 12 HOURS NO 2.7E-2 NO PPR-SRV-OO-1VLV ONE SRV FAILS TO CLOSE NO 8.8E-2 NO SRV SRVS FAILS TO CLOSE NO 8.9E-2 NO EPS-DGN-TM-DG2 DIESEL GENERATOR 2 UNAVAILABLE DUE TO TEST AND MAINTENANCE NO 3.1E-2 NO EPS-DGN-CF-START COMMON CAUSE FAILURE OF DGS TO START NO 2.8E-4 NO EPS-DGN-CF-RUN COMMON CAUSE FAILURE OF DGS TO RUN NO 4.3E-4 NO Notes:

1 Basic event was affected by the operating condition. Basis for probability change is documented in Modeling Assumptions section of this report.

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Table 5 - Uncertainty values for the operating condition Plant: Columbia Generating Station IR ID: 50-397/2002-005 SDP: EA-02-107 LER: 397-2002-001-00 Analysis type: Monte Carlo Samples: 10000; Seeds: 97453 Initiating event (IE)

IE ID Point estimate mean estimate 5% estimate 50% estimate 95% estimate All internal initiating events CCDP for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 2.278E-09 2.358E-09 3.000E-10 1.194E-09 7.509E-09 CDP for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 1.097E-09 1.182E-09 1.483E-10 5.728E-10 3.631E-09 CCDP for 5216 hours0.0604 days <br />1.449 hours <br />0.00862 weeks <br />0.00198 months <br /> 1.188E-05 1.230E-05 1.565E-06 6.228E-06 3.917E-05 CDP for 5216 hours0.0604 days <br />1.449 hours <br />0.00862 weeks <br />0.00198 months <br /> 5.722E-06 6.165E-06 7.735E-07 2.988E-06 1.894E-05 Importance for 5216 hours0.0604 days <br />1.449 hours <br />0.00862 weeks <br />0.00198 months <br /> 6.160E-06 6.134E-06 7.913E-07 3.240E-06 2.023E-05

LER 397/02-001 SENSITIVE - NOT FOR PUBLIC DISCLOSURE SENSITIVE - NOT FOR PUBLIC DISCLOSURE 10 V A 2 LO N G-T E R M LO W P R E S S IN J E C TI ON C V S C O N TA IN M E N T V E N T IN G C S S C O N T AI N M E N T S P R A Y S D C S H U TD O W N C O OL IN G D E P M A N U A L R E A C TO R D E P R ES S S P C S U P PR E S SIO N P O OL C OO LIN G VA AL TE R N A TE LOW P R E S S IN JE C T I ON LC I LP C I L C S L P C S D E P M A N U A L R E A C T O R D E P R E S S R C I R C I C H C S H P C S S R V S R V 'S C L OS E E P S E M E R G E N C Y P O W E R R P S R E AC TO R S H U TD O W N IE -L O O P LOS S OF OFF S I TE PO W E R S TA T E 1

OK 2

OK 3

OK 4

OK 5

C D 6

OK 7

OK 8

C D 9

OK 10 OK 11 OK 12 OK 13 C D 14 C D 15 OK 16 C D 17 OK 18 OK 19 OK 20 OK 21 C D 22 OK 23 OK 24 OK 25 OK 26 C D 27 OK 28 OK 29 OK 30 OK 31 C D 32 C D 33 C D 34 T

LO OP -1 35 T

LO OP -2 36 T

S B O 37 C D P 1 P 2 S P 1 S D 1 C S 1 L O O P - LO S S O F O F F S I T E P O W E R 2 00 1 /1 2/06 Figure 1 - Columbia Generating Station-Loss of Offsite Power Event Tree showing Sequence 05

LER 397/02-001 SENSITIVE - NOT FOR PUBLIC DISCLOSURE SENSITIVE - NOT FOR PUBLIC DISCLOSURE 11 DG 1 4.3E-4 E P S-DGN-CF-RUN 2.8E -4 E PS -DGN-CF-STA RT FALS E E PS -DGN-MOC-1A DG1-1 9.0E-5 ACP -BA C-LP -DI 2.3E -6 DCP -BA T-CF-A LL 4.0E -4 DCP -B AT-LP-B 11 9.0E -5 DCP -BDC-LP-S 11 DG1-2 1.1E-2 EP S -DGN-FR-DG1 9.0E-3 E P S-DGN-FS -DG1 3.1E -2 E PS -DGN-TM-DG1 1.0E -3 E PS -DGN-X R-DG1 DG N-S SWA DIE SE L GE NE RAT OR 1 FA ULTS DIE SE L G ENE RAT OR 1 ELE CTRICA L FA ILURE S DIE SE L G ENE RAT OR 1 F AI LURE S ST ANDB Y SE RV ICE W AT ER LOOP A FA ILS T O DG 1 COMM ON CA US E FA ILURE OF DGS TO RUN COMMO N CA USE FA ILURE OF DGS TO ST ART CCF O F 125V DC B ATTE RYS DIV IS ION I 125V DC B AT TERY B 1-1 FA ILS DI VISION I 125V DC B US S 1-1 FAILS DI ES E L GE NE RATO R 1 FA ILS TO RUN DIES EL GE NERA TO R F AILS TO ST ART DIES EL GE NERA TOR 1 UNA V AILAB LE DUE T O TE S T AND MA INT ENA NCE O P FA ILS TO RE S TORE DIES E L GENE RA TOR 1 DIV IS ION I AC PO WE R B USE S FA IL DIE S EL GE NE RA TOR FA ILS T O STA RT Figure 2 - WNPS - DIESEL GENERATOR 1 FAULTS

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DG2 4.3E-4 EPS-DGN-CF-RUN 2.8E-4 EPS-DGN-CF-START FALSE EPS-DGN-MOC-1B DG2-1 9.0E-5 ACP-BAC-LP-DII 2.3E-6 DCP-BAT-CF-ALL 4.0E-4 DCP-BAT-LP-B12 9.0E-5 DCP-BDC-LP-S12 DG2-2 1.1E-2 EPS-DGN-FR-DG2 9.0E-3 EPS-DGN-FS-DG2 3.1E-2 EPS-DGN-TM-DG2 1.0E-3 EPS-DGN-XR-DG2 DGN-SSWB DIESEL GENERATOR 2 FAULTS DIESEL GENERATOR 2 ELECTRICAL FAILURES DIESEL GENERATOR 2 FAILURES STANDBY SERVICE WATER LOOP B FAILS TO DG 2 COMMON CAUSE FAILURE OF DGS TO RUN COMMON CAUSE FAILURE OF DGS TO START DIESEL GENERATOR 2 FAILS TO RUN DIESEL GENERATOR 2 FAILS TO START DIESEL GENERATOR 2 UNAVAILABLE DUE TO TEST AND MAINTENANCE OP FAILS TO RESTORE DIESEL GENERATOR 2 DIVISION II 125VDC BUS S1-2 FAILS DIVISION II 125V DC BATTERY B1-2 FAILS CCF OF 125V DC BATTERYS DIVISION II AC POWER BUSES FAIL DIESEL GENERATOR FAILS TO START Figure 3 - WNPS - DIESEL GENERATOR 2 FAULTS LER 397/02-001

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LCS 1.2E-4 LCS-ST R-PG-LPCS 1.0E-3 O PR-XHE-XE-LPINJ 1.0E-6 RHR-STR-CF-SPOOL LCS-1 DIV-1-AC DIV-1-DC LCS-2 1.0E-4 LCS-CKV-CC-V3 1.0E-4 LCS-CKV-CC-V6 7.2E-4 LCS-MDP-FR-P1 3.0E-3 LCS-MDP-FS-P1 F ALSE LCS-M DP-M OC-P1 2.0E-3 LCS-M DP-TM -P1 1.0E-3 LCS-MDP-XR-P1 3.0E-3 LCS-MOV-CC-11

3. 0E-3 LCS-MOV-CC-V5 RBEC-FAN5 SSW -A STANDBY SERVI CE W ATER LO OP A F AI LS RBEC FAN 5 FAILS DIVI SION I 125VDC PO WER FAILS DIVISION I AC PO WER FAILS LPCS SYSTEM FAILURES FAILURE O F LCS TRAIN A PO WER SUPPLYS FAILURES OF LCS M DP LCS MDP FAILS TO START LCS MDP FAILS TO RUN LCS MDP UNAVAILABLE DUE TO T EST AND M AI NTENANCE OP FAILS TO RESTORE LCS M DP LPCS SUPPRESSION POO L STRAI NER PLUGS LCS RECIRC LINE ISO L MOV FCV-11 FAILS T O O PEN LCS MDP DISCH CHECK VALVE FAILS TO OPEN LCS INJECT ION ISOL MOV V-5 F AI LS TO OPEN LCS INJECT ION CHECK VALVE V-6 FAI LS TO OPEN OPERATOR FAILS TO START/CONT ROL LP INJECTION ECCS SUPPRESSION POOL ST RAINERS F AI L FROM CO MMO N CAUSE LCS MDP F AI LS TO ST ART Figure 4 - WNPS - CORE SPRAY SYSTEM FAILS

LER 397/02-001 SENSITIVE - NOT FOR PUBLIC DISCLOSURE SENSITIVE - NOT FOR PUBLIC DISCLOSURE 14 14 RHR-MDPA 1.0E-4 RHR-CKV-CC-31A 7.2E-4 RHR-MDP-FR-1A 3.0E-3 RHR-MDP-FS-1A FALSE RHR-MDP-MOC-1A 2.0E-3 RHR-MDP-TM-1A 1.0E-3 RHR-MDP-XR-1A RBEC-FAN2 RHR-MDPA-1 DIV-1-AC DIV-1-DC SSW-A FAILURE OF RHR MDP 1A POWER SUPPLYS STANDBY SERVICE WATER LOOP A FAILS FAILURES OF RHR MDP 1A DIVISION I 125VDC POWER FAILS DIVISION I AC POWER FAILS RBEC FAN 2 FAILS RHR MDP 1A DISCH CHECK VALVE FAILS TO OPEN RHR MDP 1A FAILS TO START RHR MDP 1A FAILS TO RUN RHR MDP 1A UNAVAILABLE DUE TO TEST AND MAINTENANCE OP FAILS TO RESTORE RHR MDP 1A RHR MAD FAILS TO START Figure 5 - WNPS - FAILURES OF RHR MDP 1A

LER 397/02-001 SENSITIVE - NOT FOR PUBLIC DISCLOSUR E SENSITIVE - NOT FOR PUBLIC DISCLOSURE 15 15 RHR-MDPB 1.0E-4 RHR-CKV-CC-31B 7.2E-4 RHR-MDP-FR-1B 3.0E-3 RHR-MDP-FS-1B FALSE RHR-MDP-MOC-1B 2.0E-3 RHR-MDP-TM-1B 1.0E-3 RHR-MDP-XR-1B RBEC-FAN3 RHR-MDPB-1 DIV-2-AC DIV-2-DC SSW-B FAILURE OF RHR MDP 1B POWER SUPPLYS STANDBY SERVICE WATER LOOP B FAILS FAILURES OF RHR MDP 1B RBEC FAN 3 FAILS DIVISION II 125VDC POWER FAILS DIVISION II AC POWER FAILS RHR MDP 1B FAILS TO START RHR MDP 1B FAILS TO RUN RHR MDP 1B UNAVAILABLE DUE TO TEST AND MAINTENANCE OP FAILS TO RESTORE RHR MDP 1B RHR MDP 1B DISCH CHECK VALVE FAILS TO OPEN RHR MAD FAILS TO START Figure 6 - WNPS - FAILURES OF RHR MDP 1B

LER 397/02-001 SENSITIVE - NOT FOR PUBLIC DISCLOSURE SENSITIVE - NOT FOR PUBLIC DISCLOSURE 16 16 RHR-MDPC 1.0E-4 RHR-CKV-CC-31C 7.2E-4 RHR-MDP-FR-1C 3.0E-3 RHR-MDP-FS-1C FALSE RHR-MDP-MOC-1C 2.0E-3 RHR-MDP-TM-1C 1.0E-3 RHR-MDP-XR-1C RBEC-FAN1 RHR-MDPC-1 DIV-2-AC DIV-2-DC SSW-B FAILURE OF RHR MDP 1C POWER SUPPLYS FAILURES OF RHR MDP 1C STANDBY SERVICE WATER LOOP B FAILS DIVISION II 125VDC POWER FAILS DIVISION II AC POWER FAILS RBEC FAN 1 FAILS RHR MDP 1C FAILS TO START RHR MDP 1C FAILS TO RUN RHR MDP 1C UNAVAILABLE DUE TO TEST AND MAINTENANCE OP FAILS TO RESTORE RHR MDP 1C RHR MAD FAILS TO START RHR MDP 1C DISCH CHECK VALVE FAILS TO OPEN Figure 7 - WNPS - FAILURES OF RHR MDP 1C

LER 397/02-001 SENSITIVE - NOT FOR PUBLIC DISCLOSURE SENSITIVE - NOT FOR PUBLIC DISCLOSURE 17 17 SSW-A 1.0E-4 SSW-CKV-CC-1A 7.2E-4 SSW-MDP-FR-1A 3.0E-3 SSW-MDP-FS-1A FALSE SSW-MDP-MOC-1A 2.0E-3 SSW -MDP-TM-1A 1.0E-3 SSW-MDP-XR-1A DIV-1-AC DIV-1-DC STANDBY SERVICE WATER LOOP A FAILS DIVISION I 125VDC POWER FAILS DIVISION I AC POW ER FAILS STBY SERVICE WATER PUMP 1A FAILS TO RUN SSW MDP 1A UNAVAILABLE DUE T O TEST AND MAINTEN ANCE OP FAILS TO RESTORE STBY SERVICE WATER PUMP 1A SSW MDP 1A DISCH CHECK VALVE SW-V-1A FAILS TO OPEN STBY SERVICE WATER PUMP FAILS TO START STBY SERVICE WATER PUMP 1A FAILS TO START Figure 8 - WNPS - STANDBY SERVICE WATER LOOP A FAILS

LER 397/02-001 SENSITIVE - NOT FOR PUBLIC DISCLOSURE SENSITIVE - NOT FOR PUBLIC DISCLOSURE 18 18 SSW-B 1.0E-4 SSW -CKV-CC-1B 7.2E-4 SSW-MDP-FR-1B 3.0E-3 SSW -MDP-FS-1B FALSE SSW -MDP-MOC-1B 2.0E-3 SSW -MDP-TM-1B 1.0E-3 SSW-MDP-XR-1B DIV-2-AC DIV-2-DC STANDBY SERVICE W ATER LOOP B FAILS DIVISION II 125VDC POW ER FAILS DIVISION II AC POW ER FAILS STBY SERVICE WATER PUMP 1B FAILS TO START STBY SERVICE W ATER PUMP 1B FAILS TO RUN SSW MDP 1B UNAVAILABLE DUE T O TEST AND MAINTEN ANCE OP FAILS TO RESTORE STBY SERVICE W ATER PUMP 1B SSW MDP 1B DISCH CHECK VALVE SW-V-1B FAILS TO OPEN STBY SERVICE WATER PUMP FAILS TO START Figure 9 - WNPS - STANDBY SERVICE WATER LOOP B FAILS