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 Final Precursor Analysis Accident Sequence Precursor Program --- Office of Nuclear Regulatory Research May 17, 2004 Columbia Generating Unreliable Breakers for Four Safety-Related Systems Station Event Date: 02/14/2002 LER: 397/02-001 CDP = 6x10-6 397/2002-001-00 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).

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SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001

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 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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SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 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 SENSITIVE - NOT FOR PUBLIC DISCLOSURE 3

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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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SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 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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SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 Table 1. Conditional probabilities (point values) for the dominant sequences Conditional core damage Core damage probability Event tree Sequence probability (CCDP) (CDP) Importance name no. (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 SENSITIVE - NOT FOR PUBLIC DISCLOSURE 6

SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 Table 3a. CCDP cut sets for LOOP Sequence 05 CCDP Percent Minimal cut sets1 contribution 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 Minimal cut sets1 contribution 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 2

1.4E-006 Total

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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SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 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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SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 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 SENSITIVE - NOT FOR PUBLIC DISCLOSURE 9

SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 Figure 1 - Columbia Generating Station- Loss of Offsite Power Event Tree showing Sequence 05 LO S S O F R E AC TO R E M E R G E NCY S R V 'S H P CS RCIC M A NUA L LP CS LP C I AL T E R N A TE S U P PR E S SI O N M A NU A L S H U TD O W N C O N T AI N M E N T C O N TA IN M E N T LO N G - T E R M O FF S I TE S H U TD O W N PO WER C L OS E RE A CT OR LO W P R E S S P O OL R E A C TO R C O O L IN G S P RA Y V E N T IN G LO W P R E S S PO W E R DE P RE S S IN J E C T I O N C O O LI N G D E P R ES S IN J E C TI O N IE -L O O P RPS EPS S RV H CS RCI DE P LCS LC I VA SPC DE P S DC CS S CV S VA2 # S TA T E 1 OK 2 OK 3 OK 4 OK 5 CD 6 OK 7 OK 8 CD 9 OK 10 OK 11 OK 12 OK 13 CD 14 CD 15 OK 16 CD 17 OK 18 OK 19 OK 20 OK 21 CD 22 OK 23 OK 24 OK 25 OK 26 CD 27 OK 28 OK SP1 29 OK S D1 30 OK CS 1 31 CD 32 CD 33 CD P1 34 T LO O P - 1 P2 35 T LO O P - 2 36 T SBO 37 CD L O O P - LO S S OF O F F SI T E P OW ER 2 0 0 1 /1 2 / 0 6 SENSITIVE - NOT FOR PUBLIC DISCLOSURE 10

SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 Figure 2 - WNPS - DIESEL GENERATOR 1 FAULTS DIE SE L GE NE RAT OR 1 FA ULTS DG 1 COMM ON CA US E COM MO N CA USE DIE S EL GE NE RA TOR DIE SE L G ENE RAT OR FA ILURE OF DGS FA IL URE OF DGS FA ILS T O STA RT 1 EL E CTRICA L TO RUN TO ST ART FA ILURE S 4 .3E- 4 2.8E - 4 FALS E E P S-DGN- CF-RUN E PS -DGN- CF-STA RT E PS -DGN-M OC- 1A DG1 -1 DIV IS ION I AC CCF O F 125V DIV IS ION I 125 V DI VISION I 125V DC PO W E R B USE S FA IL DC B ATTE RYS DC B AT TERY B 1-1 B US S 1-1 FAILS FA ILS 9.0 E-5 2.3E -6 4.0 E -4 9 .0 E -5 ACP - BA C-LP -DI DCP -BA T-CF- A LL DCP -B AT-LP-B 11 DCP -BDC- LP- S 11 DIE SE L G ENE RAT OR ST ANDB Y SE RV ICE 1 F AI LURE S W AT ER LOOP A FA ILS T O DG 1 DG1- 2 DG N-S SW A DIES EL GE NERA TOR O P FA IL S TO DI ES E L GE NE RATO R DIES EL GE NERA TO R 1 UNA V AIL AB LE RE S TORE DIES E L 1 FA ILS TO RUN F AILS TO ST ART DUE T O TE S T AND GENE RA TOR 1 MA INT ENA NCE 1 .1E-2 9 .0E- 3 3.1E - 2 1.0E -3 EP S -DGN- FR-DG1 E P S-DGN- FS -DG1 E PS -DGN- TM-DG1 E PS -DGN-X R-DG1 SENSITIVE - NOT FOR PUBLIC DISCLOSURE 11

Figure 3 - WNPS - DIESEL GENERATOR 2 FAULTS LER 397/02-001 DIESEL GENERATO R 2 FAUL TS DG2 COMMON CAUSE COMMON CAUSE DIESEL GENER ATOR DIESEL GENERATOR FAILURE OF DGS FAILURE OF DGS FAILS TO START 2 ELECTRICAL TO R UN TO START FAI LURES 4.3E-4 2.8E-4 FALSE EPS-DGN-CF-RUN EPS-DGN-CF-START EPS-DGN-MOC-1B D G2-1 DIVISION II CCF OF 125V DIVISION II DIVI SION II AC PO WER BUSES DC BATTER YS 12 5V DC BATTERY 125VDC BUS S1-2 FAIL B1-2 FAILS FAI LS 9.0 E-5 2.3E-6 4.0 E-4 9. 0E-5 ACP-BAC-LP-DII DCP-BAT-C F-ALL DCP-BAT-LP-B12 DCP-BDC-LP-S12 DI ESEL GENERATOR STANDBY SERVICE 2 FAILURES WATER LOOP B FAILS TO D G 2 DG2-2 DGN-SSWB DIESEL GENERATOR OP FAILS TO DIESEL GENERATOR D IESEL GENERATOR 2 UNAVAILABLE 2 FAILS TO RUN 2 FAILS TO START RESTORE DIESEL DUE TO TEST AND GENERATOR 2 MAINTENANCE 1.1E-2 9.0E-3 3.1E-2 1.0E-3 EPS-DGN-FR-DG2 EPS-DGN-FS-DG2 EPS-DGN-TM-DG2 EPS-DGN-XR-DG2 SENSITIVE - NOT FOR PUBLIC DISCLOSURE 12 2

SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 Figure 4 - WNPS - CORE SPRAY SYSTEM FAILS LPCS S YS TE M FA ILURES LCS LP CS SUP P RE SSION OP ERA TOR FA ILS E CCS SUP PRE S SION FAILURE O F LCS P OO L S TRAI NER TO S TA RT/CONT ROL P OOL ST RA INERS TRA IN A PO WE R P LUGS LP INJE CTION F AI L FROM CO MMO N S UP PLY S CA USE 1.2E -4 1.0E- 3 1.0E - 6 LCS -ST R-P G- LPCS O PR- XHE- X E-LP INJ RHR-S TR- CF -S P OOL LCS -1 DIV IS ION I A C DIVI SION I 125V DC PO WER FA ILS PO WE R FA ILS DIV A C DIV- 1-DC FAILURES OF RBE C F AN 5 FA ILS STANDB Y SERVI CE LCS M DP W ATER LO OP A F AI LS LCS -2 RBE C-FA N5 S SW -A LCS M DP DIS CH LCS INJE CT ION LCS M DP FA ILS LCS M DP FAILS CHE CK VA LVE FA ILS CHECK VA LVE V-6 TO RUN TO S TA RT TO OPE N FAI LS TO OP EN 1.0E -4 1.0E- 4 7.2E - 4 3.0E -3 LCS -CKV -CC-V3 LCS- CKV -CC-V 6 LCS - MDP - FR-P 1 LCS -MDP -FS -P 1 LCS MDP F AI LS LCS MDP UNA VA ILAB LE OP FAILS TO LCS RE CIRC LINE LCS INJECT ION TO ST ART DUE TO T ES T AND RE S TORE LCS M DP ISO L M OV FCV-11 IS OL MOV V - 5 M AI NTE NA NCE FA ILS T O O PE N F AI LS TO OP EN F ALS E 2.0E-3 1.0E- 3 3.0E- 3 3. 0E-3 LCS -M DP-M OC-P 1 LCS-M DP-TM -P1 LCS -M DP- X R-P 1 LCS- M OV -CC- 11 LCS -M OV -CC-V 5 SENSITIVE - NOT FOR PUBLIC DISCLOSURE 13 3

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

SENSITIVE - NOT FOR PUBLIC DISCLOSUR E LER 397/02-001 Figure 6 - WNPS - FAILURES OF RHR MDP 1B FAILURES OF RHR MDP 1B RHR-MDPB RHR MDP 1B DISCH RHR MDP 1B FAILS RHR MDP 1B FAILS RHR MAD FAILS CHECK VALVE FAIL S TO RUN TO START TO START TO OPEN 1.0E-4 7.2 E-4 3.0 E-3 FALSE RHR-CKV-CC-31B RHR-MDP-FR-1B RHR-MDP-FS-1B RHR- MDP-MOC-1B RHR MDP 1B UNAVAILABLE OP FAILS TO RBEC FAN 3 FAILS FAILURE OF RHR STANDBY SERVICE DUE TO TEST AND RESTORE RHR MDP MDP 1B POWER WA TER LOOP B MAI NTENANCE 1B SUPPLYS FAILS 2.0 E-3 1.0E-3 RHR-MDP-TM-1 B RHR- MDP-XR-1B RBEC-FAN3 RHR-MDPB-1 SSW-B DIVISION II DIVISION II AC POW ER FAILS 12 5VDC POWER FAILS DIV-2-AC DIV-2-DC SENSITIVE - NOT FOR PUBLIC DISCLOSURE 15 15

SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 Figure 7 - WNPS - FAILURES OF RHR MDP 1C FAILURES OF R HR MDP 1C RHR-MDPC RH R MDP 1C DISCH RHR MDP 1C FAILS RHR MDP 1C FAIL S R HR MAD FAILS C HECK VALVE FAIL S TO RUN TO START TO START TO OPEN 1.0E-4 7.2 E-4 3.0 E-3 FALSE RHR-CKV-CC-31C RH R-MDP-FR-1C RHR-MDP-FS-1C RHR- MDP-MOC-1C RHR MDP 1 C UNAVAILABLE OP FAILS TO RBEC FAN 1 FAILS FAILURE OF RHR STANDBY SERVICE DUE TO TEST AND RESTORE RHR MDP MDP 1C POWER WA TER LOOP B MAI NTENANCE 1C SUPPLYS FAILS 2.0 E-3 1.0E-3 RHR-MDP-TM-1 C RHR- MDP-XR-1C RBEC -FAN1 RHR-MDPC-1 SSW-B DIVISION II DIVISION II AC POW ER FAILS 12 5VDC POWER FAILS DIV-2-AC DIV-2-DC SENSITIVE - NOT FOR PUBLIC DISCLOSURE 16 16

SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 Figure 8 - WNPS - STANDBY SERVICE WATER LOOP A FAILS STANDBY S ERVICE W ATER LOOP A FAILS SS W- A SSW MDP 1A DISCH S TBY S ERV ICE STB Y SE RVICE S TBY SERVICE CHE CK VA LV E S W-V-1A W ATE R PUMP 1A WATER P UMP 1A WA TER P UMP FAILS FAILS TO OPE N FAILS TO RUN FA ILS TO S TART TO S TART 1.0E -4 7.2E-4 3.0E -3 FA LSE SSW -CK V-CC- 1A SS W- MDP-FR- 1A S SW -MDP -FS -1A SSW -MDP -MOC- 1A SS W MDP 1A UNA VA ILABLE OP FA ILS TO DIVISION I AC DIVISION I 125V DC DUE T O TES T AND RES TORE STB Y PO W ER FAILS P OW E R FAILS MAINTEN ANCE SE RVICE W A TER P UMP 1A 2.0E -3 1.0E-3 SSW -MDP -TM-1A SS W- MDP-X R-1A DIV AC DIV- 1-DC SENSITIVE - NOT FOR PUBLIC DISCLOSURE 17 17

SENSITIVE - NOT FOR PUBLIC DISCLOSURE LER 397/02-001 Figure 9 - WNPS - STANDBY SERVICE WATER LOOP B FAILS STA NDBY S ERV ICE W ATE R LOOP B FAILS SS W- B SS W MDP 1B DISCH S TBY S ERV ICE STB Y SE RVICE S TBY SERVICE CHE CK VALV E S W- V-1 B W ATE R PUMP 1 B WA TER P UMP 1B WA TER P UMP FAIL S FA ILS TO O PE N FAILS TO RUN FA ILS TO START TO S TART 1.0E -4 7 .2E-4 3.0E -3 FA LS E S SW -CK V-CC-1B SS W-MDP-FR- 1B S SW -MDP -FS -1B SSW -MDP -MOC- 1B SS W MDP 1 B UNA VA ILAB LE O P FA ILS TO DIV ISION II DIVISIO N II DUE T O TES T AND RES TO RE STBY 125VDC P OW ER SE RVICE W A TER AC POW ER FA ILS MAINTEN ANCE FA ILS PUMP 1B 2.0E -3 1 .0E-3 S SW -MDP -TM-1B SS W-MDP-X R-1B DIV AC DIV-2-DC SENSITIVE - NOT FOR PUBLIC DISCLOSURE 18 18