ML20135H309

Final ASP Analysis - Point Beach 1 and 2 (LER 266-94-002)

ML20135H309
Person / Time
Site:	Point Beach
Issue date:	05/14/2020
From:	Christopher Hunter NRC/RES/DRA/PRB
To:
Littlejohn J (301) 415-0428
References
LER 266-1994-002
Download: ML20135H309 (6)

Text

ADDendix C LER No. 266/94-002 ADDendix C LER No. 266/94-002 C.6 LER No. 266/94-002 Event

Description:

Both Diesel Generators Inoperable Date of Event:

February 8, 1994 Plant: Point Beach 1 and 2 C.6.1 Summary Point Beach Units I and 2 were operating at 100% power when emergency diesel generator (EDG) (302 was taken out of service for maintenance. Plant technical specifications require that, if one EDG is removed from service, the other must be tested daily to verify its operability. When the EDG remaining in service was tested, electric fuel pump and exciter failures were experienced, and the EDG was declared inoperable. Both EDGs were, therefore, simultaneously unavailable. These unavailabilities would have impacted the Point Beach plant response to a loss-of-offsite power (LOOP) had it occurred during the unavailability period. The conditional core damage probability estimated for this event, 1.2 x 10-, is applicable to both units.

C.6.2 Event Description EDG (302, the B train emergency power source for bothunits at Point Beach, was removed from service for maintenance at 0339 hours0.00392 days <br />0.0942 hours <br />5.605159e-4 weeks <br />1.289895e-4 months <br /> on February 7, 1994. At 0753 hours0.00872 days <br />0.209 hours <br />0.00125 weeks <br />2.865165e-4 months <br /> on February 8, 1994, an operability test of the A train emergency power source, EDG (301, was begun. At 0951 hours0.011 days <br />0.264 hours <br />0.00157 weeks <br />3.618555e-4 months <br /> trouble annunciations were received for that EDG.

Investigation determined that the electric fuel pump for EDO (301 had failed. The EDG continued to run, however, with fuel supplied by a shaft-driven mechanical pump. The diesel was allowed to continue to rum unloaded while repairs were made to the electric fuel pump. At 1940 hours0.0225 days <br />0.539 hours <br />0.00321 weeks <br />7.3817e-4 months <br /> repairs were complete, and the EDG was shut down.

At 2046 hours0.0237 days <br />0.568 hours <br />0.00338 weeks <br />7.78503e-4 months <br /> EDG GO01 was started and loaded for a hard run to clean its exhaust system of deposits accumulated during the prior prolonged no-load rum. At 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br /> power swings were noted on the EDG varmeter. These swings increased in intensity, and at 2204 hours0.0255 days <br />0.612 hours <br />0.00364 weeks <br />8.38622e-4 months <br /> EDO (301 was declared inoperable.

A stationary brush jumper cable in the ED 0's exciter was found to be contacting a rotating bus bar, shorting out the dc excitationvoltage. This condition was repaired, and the EDG was declared operable at 0244 hours0.00282 days <br />0.0678 hours <br />4.034392e-4 weeks <br />9.2842e-5 months <br /> on February 9, 1994.

C.6.3 Additional Event-Related Information The Licensee Event Report (LER) for this event indicates that the brush jumper cable was installed incorrectly during an annual maintenance outage on February 3, 1994. The report further indicates that EDG (301 was run for 3 h on February 4, 1.9 h on February 7, and 10.3 h on February 8 (while the electric fuel pump was repaired). The LER also indicates that a gas turbine generator was available as a backup source of emergency ac power.

C.6.4 Modeling Assumptions This event was modeled as a 47-h simultaneous unavailability of both EDGs. As it was out of service for maintenance, EDG (302 was assumed to be unavailable after 0339 hours0.00392 days <br />0.0942 hours <br />5.605159e-4 weeks <br />1.289895e-4 months <br /> on February 7, 1994. EDG (301 experienced fuel pump and exciter failures that resulted in its being declared inoperable on February 8, 1994. After investigation, the exciter failure was attributed to maintenance errors that occurred on February 3, 1994. EDO (301 was operated on occasion between February 3 and February 8; however, the EDG ran unloaded for most of tbis time. After it was restarted to run under C.6-1 C.6-1NUREGICR-4674, Vol. 21

LER No. 266/94-002 Appendix C load on February 8, the EDG only operated for about 15 min before erratic exciter performance was observed. While it is possible that the EDG could have successfully run for an extended time in a loaded condition, this analysis assumes EDG (301 was unavailable to perform its safety function of supplying long-term emergency power until the exciter repair was completed on February 9, 1994. Due to the nature of the EDGunavailabilities, no EDGrecovery was assumed to be possible. Because ofthe unavailability ofbothllDGs, the core damage sequences of primnary poncemninthis analysis are those associated with a postulated LOOP and subsequent station blackout.

The probability of a LOOP inthe 47-h period, the probability of its short-term and long-term recovery, and the probability of a reactor coolant pump (RCP) seal loss-of-coolant accident (LOCA) following a postulated station blackout were developed based on data contained in NUREG-1032, Evaluation ofStation BlackoutAccidents atNuclearPowerPlants, and RCP seal loss-of-coolant (LOCA) models developed as part of the NUREG-1150 probabilistic risk assessment (PRA) efforts, as described in Revised LOOP Recovery and PWR Seal LOCA Models, ORNL/NRCILTR-89/l 1, August 1989.

The Final Safety Analysis Report (FSAR) indicates that a gas turbine generator is available at the Point Beach site that can be started and loaded within 10 muin. This gas turbine generator is credited as a source of emergency ac power in the Point Beach Individual Plant Examination (LPE), and failure to recover ac power using the gas turbine is assigned aprobability of 0. 13 inthe WPE. That value is employed inthis analysis for the probability of failure to recover emergency ac power.

The IRRAS-based ASP model for Point Beach was modified to reflect the conditions observed during the event by setting the independent failure basic events associated with each EDG (EPS-DGN-FC-lA, B) to true, the EDG common-cause failure basic event (EPS-DGN-CF-AIL) to false, and the emergency power nonrecovery probability (EPS-XIHE-NOREC) to 0.13. Basic events and their probabilities are shown in Table C.6. 1. The incremental core damage probability over 47 h was then calculated by re-solving the accident sequence model.

The current ASP LOOP model for Point Beach assumes that the PORVs will be challenged, and that they will fail to reclose with a probability of 3 x 10-3 (IRRAS model default value) each. This assumption may be conservative, but it did not affect the dominant sequence for the event.

Calculations were performed for Point Beach Unit 1, the unit reported in the LER. Since EDG GO1I and (302 also provide emergency power for Unit 2, the calculations are equally applicable to that unit.

The ESAR for Point Beach also indicates that the station batteries are designed to carry shutdown loads following a plant trip and loss of all ac power for a period of 1 h. Information provided by Point Beach indicates that the expected battery lifetime is 2 h. This analysis was performed based on the expected 2 h battery lifetime.

C.6.5 Analysis Results The estimated conditional core damage probability associated with this event at each unit is 1.2 x 10-. The dominant core-damage sequence, highlighted on the event tree in Figure C.6. 1, involves a postulated loss-of-offsite power, unavailability of emergency power because of the unavailability of both EDGs, failure to recover emergency power through use of the gas turbine generator, RCP seal LOCA, and failure to recover ac power prior to core uncovery.

Definitions and probabilities for selected basic events are shown in Table C.6. 1. The conditional probabilities associated with the highest probability sequences are shown in Table C.6.2. Table C.6.3 lists the sequence logic associated with the sequences listed in Table C.6.2. Table C.6.4 describes the system names associated with the dominant sequences.

Cutsets associated with each sequence are shown in Table C.6.5.

C.6.6 Reference I1. LER 266/94-002, "Inoperability of Both Emergency Diesel Generators," March 9, 1994.

NIJREGICR-4674, VoL 21 C.6-2

Amendix C LER No. 266/94-002 Appendix C LER No. 266/94-002 Figure C.6. 1. Dominant core damage sequence for LER 266/94-002.

C.6-3 C.6-3 NIREGICR-4674, Vol.21

LER No. 266/94-002 Appendix C Table C.6.1.

Definitions and probabilities for selected basic events for LER 266/94-002 Base CrrentModified Event name Description prbaseit prreabilty Type for this probbiliy prbabiityevent AFW-TDP-FC-IA AFW Turbine Driven Pump 3.3E-002 3.3E-002 N

Fails AFW-XHEM-NOREC-EP Operator Fails to Recover 3.E01 3E01N AFW During Station Blackout 3.EOl

.4-l AFW-XIHE-XA-PSWEP Operator Fails to Align Backup 4.OE-002 4.OE-002 N

Water Source During SBO EPS-DGN-CF-ALL Common Cause Failure of two L.E-003 O.E+00 FALSE Y

diesel generators EPS-DGN-FC-lA Diesel Generator A Fails 4-2E-002 L.OE+OOO TRUE Y

EPS-DGN-FC-1B Diesel Generator B Fails 4.2E-002 L.OE+OOO TRUE Y

EPS-XI]E-NOREC Operator Fails to Recover 8.OE-OO1 1.3E-001 Y

Emergency Power rn-LOOP Loss-of-Offsite Power 5.8E-006 2.7E-004 Y

Initiating Event 1E-SGTR Steam Generator Tube Rupture O.OE+OOO O.OE+OOO Y

Initiating Event LE-SLOCA Small LOCA Initiating Event O.OE-I-OO O.OE+OOO y

LE-TRANS Transient Initiating Event O.OE+OOO O.OE+OOO y

Operator Fails to Recover OEP-XIHE-NOREC-BD Offsite Power Before Battery 8.3E-002 8.3E-002 N

Depletion OEP-XHE-NOREC-SL Operator Fails to Recover6.E01

.5-1N Offsite Power (Seal LOCA)

.- Ol 6EOlN PPR-SRV-00-PRVI PORV 1 Fails to Reclose After 3.OE-002 3.OE-002 N

Opening PPR-SRV-OO-PRV2 PORV 2 Fails to Reclose After 3.OE-002 3.OE-002 N

Opening RCS-MDP-LK-SEALS RCP Seals Fail Without 2.6E-001 2.6E-001 N

ICooling and InjectionIII NUREGICR-4674, VoL 21 C.6-4 NUREG/CR4674, Vol. 21 C.6-4

Appendix C LER No. 266/94-002 Table C.6.2.

Sequence conditional probabilities for LER 266/94-002 Even tre nme Squece ame Conditional Core damage iprac o

Evn te nm Sqenenae core damage probability (CCp-racDP

%ontribution probability (CDP)

(CPCP (CCDP)

LOOP 37 5.9E-006 3.9E-007 5.5E-006 49.4 LOOP 30 2.9E-006 1.6E-008 2.9E-006 25.8 LOOP 38 2.1E-006 5.5E-0.08 2.018-006 18.2 LOOP 39 8.7E-007 5.9E-008 8.l1E-007 7.2 Total (all sequences) 1.2E-005 Table C.6.3.

Sequence logic for LER 266/94-002 Event tree Sequence name Logic name LOOP 37 IRT-L, EP, /AFW-L-EP, PORV-L, /PORV-EP, SEALLOCA, OP-SL LOOP 30

/RT-L, EP, /AFW-L-EP, PORV-L, !PORV-EP, /SEALLOCA, OP-BD LOOP 38

/RT-L, EP, /AFW-L-EP, PORV-L, PORV-EP LOOP 39 IRT-L, EP, AFW-L-EP Table C.6.4.

System names for LER 266/94-002 System name Description AFW-L-EP No or Insufficient AFW Flow During Station Blackout EP Failure of Both Trains of Emergency Power OP-BD Operator Fails to Recover Offisite Power Before Battery Depletion OP-SL Operator Fails to Recover Offisite Power (Seal LOCA)

PORV-EP PORVs Fail to Reclose (No Electric Power)

PORV-L PORVs Open During LOOP RT-L -

Reactor Fails To Trip During LOOP SEALLOCA RCP Seals Fail During LOOP C.6-5 NUREGICR-4674, Vol.21 C.6-5 NUREG/CR4674, Vol. 21

LER No. 266/94-002 Appendix C Table C.6.5.

Conditional cut sets for higher probability sequences for LER 266/94-002 Conditional Cut set No.

%core damage Cut sets Contribution probability (CCDP)

LOOP Seq: 37 5.9E-006 1

1000 5.9-006 EPS-XI-IE-NOREC, OEP-XIHE-NOREC-SL, 1

1000 5.9-006 RCS-MDP-LK-SEALS LOOP Seq: 30 2.9E-006 1

100.0 2.9E-006 EPS-XIHE-NOREC, OEP-XHE-NOREC-BD LOOP Seq: 38 2.113-006 150.1 1.0E-006 EPS-XIHE-NOREC, PPR-SRV-00-PRVI 2

j 50.1 1 OE-006 EPS-XHE-NOREC, PPR-SRV-OO-PRV2 LOOP Seq: 39 8.7E-007 1

54.8 4.8E-007 AFW-XHE-NOREC-EP, EPS-XH-E-NOREC, AFW-XHIE-XA-PSWEP 2

4.2

.9E007 AFW-TDP-FC-lA, AFW-XI-IE-NOREC-EP, 2

45.

3.9-007 EPS-XIHE-NOREC Total (all sequences) 1.2E-005 N IJRE............oL.21......

NUREG/CR-4674, Vol. 21 C.6-6