ML20149K465
| ML20149K465 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1990-017-00 | |
| Download: ML20149K465 (5) | |
Text
B-29.1 ACCIDENT SEQUENCE PRECURSOR PROG RAM EVENT ANALYSIS LER No. 369/90-017 Event
Description:
Both emergency diesel generators unavailable Date o f Event: June 26,1990 Plant: McGuire I Summary During surveillance testing on June 26, 1990, McGuire 1 was at 100%. power when personnel discovered that both emergency diesel generators (DGs) were functionally inoperable. Personnel found that fuel rack pivot points and the exciter commutator rings had been inadvertently painted, causing failure o f both DGs. This event has been modeled as a 99.6 h unavailability o f emergency power. The conditional core damage probability estimated for this event is 2.7 x 10-4. The relative significance o f this event compared to other postulated events at McGuire 1 is shown below.
LER369/89-017-IE-7 IE-6 IE-5 1E-4 1 l 1 _____ 1____sif ^ 1 1 J1 L
- 360 hE Trip-l 1 LOEW+i j LOOP 1 MTRAFW L-360hAFW l- precursorcutoff Event Description In October o f -1988, maintenance personnel had completed painting o f DGs 2A and 2B for McGuire Unit 2. These tasks werepeiformed satisfactorily, and the operability o f the DGs was verified. In May o f 1990, discussions began between, the Operations and Maintenance personnel with respect to painting DGs 1A and IB o f McGuire Unit 1.
Subsequently, on June 14, maintenance personnel contacted operations personnel to discuss painting o f the DG engines. The operations individual contacted discussed what was to be done and stated that he was told that the same personnel who painted the Unit 2 DGs would be assigned to paint the DGs for Unit 1. Further, he stated that he had confidence in their ability due to the painters previous work in the DG rooms, and he felt that specific guidance was not necessary. Painting o f the Unit 1 DGs was started at
B-292 0800 h on June 21 and completed on June 23. On June 26 at 0905 h, Operations (OPS)
Performance Testing personnel unsuccessfully attempted to start DG 1A. The DG failed to reach 4160-V in the required 1 1 s . DG 1A was declared inoperable at 1000 h.
Subsequent investigation revealed paint overspray on the generator exciter commutator ring. Paint overspray was similarly noted on DG IB . At 1006 h, a second start was attempted. The second start time w as good, but the generator failed to fully load.
Continued investigation revealed paint on the fuel pump rack connections to the DG governor, causing the fuel pump rack to bind.
At 1134 h, OPS personnel declared DG IB inoperable to clean paint o ff the fuel pump rack connections. After removing the paint and completing operational testing, DG 1A was returned to service at 1325 h. DG IB was returned to service at 1600 h.
Planned corrective action includes requiring involvem ent o f personnel with expert equipment specific knowledge to participate on all work requests requiring painting, functional verification o f equipment operability o f safety significant equipment, and separating painting tasks so that work w ill not be performed on more than one safety-related train at a time.
A sp M odeling A ssum ptions and A pproach The LER does not specifically reference when DG IB was taken out o f service for painting. Since preparation for painting o f DG. IB was initiated on June 22, the assumed period o f emergency power unavailability is from 0800 h on June 22 to the time that DG 1A w as returned to service at 1137 h on June 26: a 99.6 h period. The DGs were assumed to be nonrecoverable (nonrecovery = 1.0) in the short term.
A n alysis R esults The conditional core damage probability estimated for this event is 2 .7 .x 10*4. The dominant sequence, highlighted on the following event tree, involves a postulated loss o f offsite power, failure o f emergency power, and failure to recover AC power prior to battery depletion. If the diesels are assumed to be locally recoverable (nonrecovery =
0.34), then the conditional cole damage probability is estimated to be 9.1 x 10*5.
B-293 PORV/ PORV/ PORV SEQ END LOOP RT/LOOP EP APW SRV SRV SEAL EPREC HPI HPR ICCA OPEN NO STATE CHAU RESEAT (U3NQ)
OK OK
{ 41 CO 42 CO OK OK 43 CO 44 CO 4S CO OK 46 CO 47 CO 46 CD OK 49 CO SO CO OK SI CD 52 CO S3 CD OK 34 CD 55 CO 40 ATWS Dominant core damage sequence for LER 369/90-017
B-294 CONDITIONAL' CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 369/90-017 Event
Description:
Both emergency diesel generators unavailable Event Date: 06/26/90 Plant: McGuire 1 UNAVAILABILITY, DURATION- 99.6 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 5.8E-04 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/lnitiator Probability.
CD LOOP 2.7B-04 Total 2.7E-04 ATMS LOOP O.OE+OO Total O.OE+OO SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
54 loop -rt/loop EMERG.POMER -afw/emerg.power -porv.or.srv.chall - CD 2.5E-04 3.6E-01 seal.loca ep.rec 49 loop -rt/loop EMERG.POMER -afw/emerg.power porv.or.srv.chall - CD 1.0E-05 3.6E-01 porv.or.srv.reseat/ernerg.power -seal.loca ep.rec 5S loop -rt/loop EMERG.POMER afw/emerg.power CD 9.9E-06 1.2E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
49 loop -rt/loop EMERG.POMER -afw/emerg.power porv.or.srv.chall - CD 1.0E-05 3.6B-01 porv.or.srv.reseat/emerg.power -seal.loca ep.rec 54 loop -rt/loop EMERG.POMER -afw/emerg.power -porv.or.srv.chall - CD 2.5E-04 3.6E-01 seal.loca ep.rec 55 loop -rt/loop EMERG.POMER afw/emerg.power CD 9.9E-06 1.2E-01
- non-recovery credit for edited ca*se 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\pwrbseal.cmp b r a n c h MODEL: c:\asp\1989\mcguire.sll PROBABILITY FILE: c:\asp\1969\pwr_bsll.pro Event Identifier: 369/90-017
B-295 No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 4.32-04 1.02+00 loop 1.6B-05 3.62-01 loee 2S4B-06 4.32-01 rt 2.8204 1.2E-0i rt/loop 0.02+00 1.02+00 EMERG.POWER 2.92-03 > 1.0E+00 8.02-01 -> 1.02+00 Branch Models l.OP.2 Train l C o n d Ptob: 5.02-02 > Failed Train 2 Cond Probs 5.72-02 > Failed afw 3.82-04 2.62-01 afw/emerg.power 5..02-02 3.42-01 mfw 1.02+00 7.02-02 1.02-03 porv.or.srv.chall 4.02-02 1.02+00 porv.ox.arv.reseat 3.02-02 1.12-02 porv .or.srv". Xfeseat/emerg .power 3.02-02 1.02+00 seal.loca 0.02+00 1.02+00 ep.rec(sl) O.OE+OO 1.02+00 ep.rec 4.52-01 1.02+00 hpi 1.02-03 8.4201 hpi(f/b) 2.22-03 8.42-01 1.02-02 hpr/-hpi 1.52-04 1.02+00 *1.02-03 porv.open 1.02-02 1.02+00 4.02-04
- branch model file
- forced MinaricSc 08-06-1991 17s31s57 Event Identifiers 369/90-017