ML20135H321
| ML20135H321 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 05/14/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1990-042-00 | |
| Download: ML20135H321 (5) | |
Text
B-242 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No: 311/90-042 Event
Description:
Safety injection and one train of emergency power unavailable Date of Event: December 20, 1990 Plant: Salem 2 Summary One train of the safety injection (SI) system and one emergency diesel generator (EDG) were unavailable for approximately 6 h. The EDG was in the process of being repaired when a leak in the service water (SW) system caused the one train of SI to be unavailable. In the event of a loss of offsite power (LOOP), the second train of SI would be unavailable because it is powered by the EDG that is also out of service. The conditional core damage probability estimated for this event is 1.3 x 10-6. The relative significance of this event compared to other postulated events at Salem 2 is shown below.
Event Description The 2B EDG was inoperable because of maintenance activities. In the event of a LOOP, this rendered the No. 22 SI pump unavailable. At 1442 on December 20, 1990, a SW through-wall leak on the inlet pipe to the No. 21 component cooling water (CCW) pump room cooler occurred. The No. 21 SW header was isolated to stop the leak. This resulted in unavailability of charging pump 22 (due to the SW line isolation) and, in the event of a LOOP, charging pump 21 (due to unavailability of EDG 2B). This also caused the Nos. 21 and 22 containment fan cooling units (CFCU) and the No. 21 containment spray (CS) pump room cooler to be inoperable. The leak caused spray to hit
B-243 both motor-driven auxiliary feedwater (AFW) pumps. These pumps were declared inoperable, but subsequent inspection and testing indicated that the pumps would have worked. The combined EDG and SW header unavailability lasted approximately 6 h.
ASP Modeling Assumptions and Approach The event has been modeled as a postulated LOOP with one EDG and the high pressure injection system unavailable. Because of the EDG unavailability, one motor-driven AFW pump was also assumed to be unavailable.
Analysis Results The conditional probability of severe core damage estimated for this event is 1.3 x 10-6.
The dominant core damage sequence, highlighted on the following event tree, involves a postulated LOOP, failure of emergency power, a subsequent seal loss-of-coolant accident (LOCA), and failure to recover emergency power prior to core uncover)'.
B-244 LOOP RTILO E PTI~~ AW OV SRRV PSRVV" OV ~A EFCIH
'C l P P P PORV SEO END L.......J...........~CHALL RESEA IfC P)NG) OEN NO STATE OK OK 41 CD 42 COD OK OK 43 CD()
44 CO C5OD OK 48 CO 47 CO 48 CO OK 49 CO 50 CO OK 51 CO 52 CO 53 CO OK 54 CO 55 CO 40 ATWS (1) OK for Class D Dominant core caamage sequence for LER 311,90-042
B-245 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 311/90-042 Event
Description:
Safety injection and one train of emergency power unavail Event Date: 12/20/90 Plant: Salem 2 UNAVAILABILITY, DURATION- 6 NON-R~ECOVERABLE INITIATING EVENT PROBABILITIES LOOP 5 .2E-05 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CO LOOP 1. 3E-06 Total 1.3E-06 ATWS LOOP O.OE+OO Total 0.OE+O0 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
53 loop -rt/loop ENERG.POWER -afw/emerg.power -porv.or.srv.chall CO 5.4E-07 4.2E-01 seal.loca ep.rec(sl) 52 loop -rt/loop ENERG.POWER -afw/emerg.power -porv.or.srv.chall CD 4.4E-07 4.2E-01 seal.loca -ep.rec(sl) NPI
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
52 loop -rt/loop EMERG.POWER -afw/emerg.power -porv.or.srv.chall CO 4.4E-07 4.2E-01 seal.loca -ep.rec(sl) HPI 53 loop -rt/loop ENERG.POWER -afw/emerg.power -porv.or.srv.chall CO 5.4E-07 4.2E-01 seal.loca ep.rec(sl)
- 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 NODEL: c:\asp\1989\pwrbseal.cmp BRANCH NODEL: c:\asp\19B9\salem2.sll PROBABILITY FILE: c:\asp\1989\pwr~bsll.pro No Recovery Limit Event Identifier: 311/90-042
B-246 BRANCH FREOUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 9.OE-04 1.OE+OO loop 1. 6E-05 5.3E-01 loca 2 .4E-06 4.3E-01 rt 2 .8E-04 1.2E-01 rt/loop O.OE+OO l.OE+OO EMERG.*POWER 7.5E-03 > 9.7E-02 8.OE-Ol Branch Model: 2.OF.3 Train 1 Cond Prob: 5.OE-02 Train 2 Cond Prob: 5.7 E-02 Train 3 Cond Prob: 1.9E-01 > Unavailable AFW 3.8E-04 > 1.3E-03 2. 6E-01 Branch Modal: l.OF.3+ser Train 1 Cond Prob: 2.OE-02 Train 2 Cond Prob: l.OE-Ol > Unavailable Train 3 Cond Prob: 5.OE-02 Serial Component Prob: 2 .8E-04 afw/emnerg. power 5.OE-02 3.4E-01 mfw 1 .OE+OO 7. OE-02 porv.or.srv.chall 4 .OE-02 1.OE+OO porv.or. srv. reseat 2 .OE-02 1.1E-02 porv.or. srv. reseat/emerg.power 2 .OE-02 1. OE+OO seal .loca 2 .7E-O1 1. OE+OO ep. rec (al) 5.7E-O1 1. OE+OO ep. rec 7 .OE-02 1.OE+OO HP I l.OE-03 > l.OE+OO 8.4E-01 > 1.OE+OO Branch Model: l.OF.2 Train 1 Cond Prob: l.OE-02 > Unavailable Train 2 Cond Prob: l.OE-Ol > Unavailable HPI (F/B) l.OE-03 > 1.OE+OO 8.4E-01 > l.OE+OO 1. OE-02 Branch Model: l.OF.2+opr Train 1 Cond Prob: l.OE-02 > Unavailable Train 2 Cond Prob: l.OE-Ol > Unavailable hpr/-hpi 1.5E-04 1.OE+OO 1.OE-03 porv. open l.OE-02 1. OE+OO 4. OE-04
- branch model file
- forced Kina rick 08-06-1991 17:33:27 Event Identifier: 311/90-042