ML20135G736
| ML20135G736 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 05/14/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 461-1990-011 | |
| Download: ML20135G736 (5) | |
Text
B-384 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER Number: 461/90-011 Event
Description:
Division 1 and 2 emergency diesels inoperable Event Date: May 13, 1990 Plant: Clinton 1 Summary Shutdown service water supplies to emergency diesel generators (EDGs) "lA" and "IB" were improperly restored following maintenance. The EDGs were left without an adequate supply of cooling water for between 1 and 2 days during a plant startup. The conditional core damage probability estimated for this event is 4.7 x 10-5. The relative significance of this event compared to other postulated events at Clinton is shown below.
1E-7 IE-6 1E-5 IE-4 11E-3 IE-2 II I F, I I I LTrip kop [L3hE cuof1 precursor cuof-J 36Oh HPCS
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Event Description Following maintenance during an outage, EDGs "lA" and "lB" were realigned for service on May 11, 1990. Operators performing the alignment misunderstood instructions that were both unclear and incorrect, and they did not sufficiently open shutdown service water supply valves to the diesels.
At 1039 h on May 14, the plant entered startup mode. At 1335 ht on May 15, EDG "lA" was started for testing, but it soon tripped off on high coolant temperature. Upon investigation, it was learned that the shutdown service water supply valve to the EDG had been opened six turns from the full-closed position. A caution tag on the valve was intended to convey that the valve should be opened six turns from the off-seat postion, but it did not clearly state this. It was also determined that neither position would have properly balanced cooling water flow to the diesel. A similar condition was found for
B-385 EDG "MB" as well, and it was declared inoperable at 1430 h.
At 1432 h, service water supply valves to EDG "iB" were adjusted and the diesel was restored to operable status. Following a similar adjustment and an inspection, EDG "IA" was restored to operable status at 0630 h on May 16. The division 3 EDG, "i1C",
remained available at all times.
Additional Event-Related Information The high coolant water temperature trip is effective only when the diesel generator is started in the test mode. Had the diesel operated in response to an emergency start signal, this trip would have been bypassed. The EDG vendor indicated that approximately 4 min of full-load operation should be required to reach the high-temperature alarm setpoint of 195TF under these circumstances. The closed-loop EDG cooling water would then begin boiling in about 2 more minutes. EDG failure could be expected as soon as 3 min after that time.
ASP Modeling Assumptions and Approach This event has been modeled as a 110 h unavailability of both ED~s. This time includes the entire unavailability period from May 11, 1990, until May 15, 1990, and may be conservative, since the time at which the plant exited cold shutdown was not specified.
The nonrecovery likelihood was assumed to be 1.0, considering the short time to EDG failure and the lack of a high-temperature EDG trip signal following a postulated LOOP.
RHR was not assumed to be impacted by the EDG unavailability, since it is only required in the long term. AC power must be recovered prior to battery depletion to prevent core damage. This is before residual heat removal (RHR) is required for long-term heat removal.
Analysis Results The conditional probability of severe core damage estimated for this event is 4.7 x 10-5.
The dominant sequence associated with the event, highlighted on the following event tree, involves a postulated loss of offsite power in the 110-h period, failure to recover emergency power, and failure to recover offsite power prior to battery depletion.
B-386 DOM4 %D"4m GHM. MODE I__ 48)E N Or*ATE 0m 0%
45 CCI DAMAGE 45 00FIEDAAG OK OK 54 COR DAM4AGE
________COW 4DAMAGE488 0K ON08MD OK OK OK 52 0GORE04AMAGE 54 0GOREDAMAGE Be AT O8 O7K 04 08CWDMG OK 55 0440840 GOE08 AO I? GR8 DMG OK ZO0 AMG so 0GOREDAMAGE OK 57 A7M Domiantcoredamge equece or ER 41/9-01
B-387 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 461/90-011 Event
Description:
Division 1 and 2 emergency diesels inoperable Event Date: 05/13/90 Plant: Clinton 1 UNAVAILABILITY, DURATION= 110 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 9.5E-04 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD Loop 4 .7E-05 Total 4 .7E-05 ATWS LOOP 0.05+00 Total 0.0E+D0 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State P rob N Rec**
83 loop EMERG.POWER -rx.shutdown/ep ep.rec CD 4. 6E-05 5.3E-01 97 loop EMERG.POWER rx.shutdown ATWS 2 .8E-08 5.3E-01 98 loop -EMERG.POWER rx.shutdown ATWS 2.85-08 2.6E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State P rob N Rec**
98 loop -EMERG.POWER rx.shutdown ATWS 2.BE-08 2.6EE-01 83 loop EMERG.POWER -rx.shutdown/ep ep.rec CD 4. 6E-05 5 .3E-01 97 loop EMERG.POWER rx.shutdown ATWS 2. 8E-08 5.3E-01
- non-recovery credit for edited case Note: For unavailabilities, conditional probability values are differential values which reflect the added risk due to failures associated with an event. Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.
SEQUENCE MODEL: c:\asp\1989\bwrcseal.cmp BRANCH MODEL: c:\asp\1989\clinton.sll PROBABILITY FILE: c:\asp\1989\bwr-csll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Event Identifier: 461/90-011
B-38 8 Branch System Non-Recov Opr Fail trans 7.12-04 1.02+00 loop 1.6E-05 5.3E-01 loca 3.3E-06 5.02-01 x.shutdown 3.02-05 1. 02+00 rx .shutdown/ep 3.5E-04 1.02+00 pcs/trans 1.7E-01 1.02+00 srv.chall/trans.-scram 1.02+00 1. 02+00 srv. chall/loop. -scram 1 .02+00 1. 02+00 srv.close 5.3E-02 1.02+00 EMERG. POWER 2.9E-03 > 1.02+00 8.02-01 > 1.02+00 Branch Model: 1.OF.2 Train 1 Cond Prob: 5.02-02 > Failed Train 2 Cond Prob: 5.7E-02 > Failed ep. rec 4.9E-02 1.02+00 fw/pcs .trans 4.62-01 3.4E-01 fw/pcs.loca 1.02+00 3. 4E-01 hpci 2.02-02 3.4E-01 rcic 6.02-02 7.02-01 crd 1.02-02 1. 02+00 1.02-02 srv.ads 3.7E2-03 7.1E-01 1. 02-02 LPCS 2.02-02 > 1.02+00 3.42-01 > 1.02+00 Branch Model: l.OF.1 Train 1 Cond Prob: 2.OE-02 > Unavailable LPCI (RHR) /LPcS 6.02-04 > 1.02+00 7.1E-01 > 1.02+00 Branch Model: l.OF.3 Train 1 Cond Prob: 2.02-02 > Unavailable Train 2 Cond Prob: 1.02-01 > Unavailable Train 3 Cond Prob: 3.02-01 > Unavailable rhr (sdc) 2.3E-02 3. 4-01 1. 02-03 rhr(sdc) /-lpci 2.02-02 3. 4E-01 1. 02-03 rhr(sdc) /lpci 1 .02+00 1. 02+00 1. 02-03 rhr(spcool) /rhr(sdc) 2.02-03 3. 4E-01 rhr(spcooi) /-lpci.rhr(sdc) 2.02-03 3. 4E-01 rhr(spcool) /lpci.rhr(sdc) 9.3E-02 1. 02+00 2225W 2.02-02 > 1.02+00 3.42-01 > 1.02+00 2.02E-03 Branch Model: l.OF.l+opr Train 1 cond Prob: 2.02-02 > Unavailable
- branch model file
- forced Minarick 08-0 6-19 91 17:31:32 Event Identifier: 461/90-011