ML20135H320
| ML20135H320 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 05/14/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1990-005-00 | |
| Download: ML20135H320 (5) | |
Text
B-233 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No.: 311/90-005 Event
Description:
HPI inoperable due to leaking weld Date of Event: January 17, 1990 Plant: Salem 2 Summary The high-pressure injection (BPI) flow path to the reactor coolant system (RCS) was isolated to stop leakage of borated water from the discharge side of the boron injection tank (BIT). 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.
LER 311/90-005 1E-7 1E- IE-5 1E-4 IE-3 IE-2 I Iz I I I I II, II L I LOFW +- 1 MTM AFW precursor cutoff -J Event Description Salem 2 was operating at 100% of rated power on January 16, 1990, when a boron leak was discovered on the discharge side of the BIT. The leak was located on a portion of the old recirculation line from the BIT to the boric acid storage tank, which had been removed and capped by a design change in 1988. The BIT inlet isolation motor-operated valves had to be closed to isolate the leak. This action not only isolated the leak, but also eliminated the cold leg injection flow path for the charging pumps; thus HPI was inoperable. The unit was shut down in accordance with Technical Specifications, and the leaking pipe was removed and replaced.
The leak was isolated at 2300 h on January 16, 1990. The plant was in Mode 4 at 1300 h on January 17, 1990, and in Mode 5 (cold shutdown) at 0808 h the next day.
B-234 A failure analysis performed on the damaged section of pipe determined that the crack that caused the leak was probably initiated at a weld defect during the installation of the pipe cap in November 1988. Crack propagation is attributed to "high frequency, low amplitude cyclic loading, which is characteristic of the positive displacement pump discharge..."
Additional Event-Related Information The emergency core cooling system (ECCS) delivers water to the RCS in the event of a loss-of-coolant accident (LOCA). Two centrifugal charging pumps are required for the high-pressure injection phase of the ECCS following a design basis LOCA. These pumps then deliver borated water at RCS pressure from the refueling water storage tank (RWST) through the BIT to the four RCS cold legs. Conversely, the safety injection pumps take a suction on the RWST and deliver borated water at approximately 1520 psig through the accumulator discharge lines to the four RCS cold legs.
ASP Modeling Assumptions and Approach This event has been modeled as an unavailability of BPI and bleed and feed following a postulated trip during plant shutdown. The likelihood of trip during the shutdown was assumed to be 0. 1. The potential for catastrophic failure of the weld prior to discovery has not been addressed in the analysis.
Analysis Results The conditional probability of severe core damage estimated for this event is 1.3 x 10-6.
The dominant sequence, highlighted on the following event tree, involves a transient-induced LOCA with failure of HPI.
B-235 LIIICHAL TRARSV/
TRNAFW MFW PO SRV PORW ISRV IRESEAT I
HPi I
HPR I
OPERN OE SEQ)
NO EN STATE OK OK 11 CD 12 CO OK OK OK 13 CD 14 Co OK OK 15 CD (1) 16 CD 17 CD 18 ATWS (1)0OK for Class D Dominant core damage sequence for LER 31 1/90-005
B-236 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 311/90-0OS Event
Description:
HPI inoperable due to leaking weld Event Date: 01/17/90 Plant: Salem 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1 .OE-Ol SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 1.3E-06 Total 1 .3E-06 ATWS TRANS 3.4E-06 Total 3.4E-06 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State P rob N Rec**
12 TRANS -rt -aft, porv.or.srv.chall porv.or.srv.reseat HPI CD 7 .4E-07 9 .2E-04 17 TRANS -rt afw mfw HPI(F/B) CD 5. 9E-07 1.5E-03 18 TRANS rt ATWS 3.4E-06 1 .2E-02
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
12 TRANS -rt -afw porv.or~srv.chall porv.or.srv.reseat NPI CD 7.4E-07 9.2 E-04 17 TRANS -rt afw mfw NPI (F/B) CD 5.9E-07 1.5SE-O3 1B TRANS rt. ATWS 3.4E-06 1 .2E-02
- non-recovery credit for edited case SEQUENCE MODEL: c :\asp\19B9\pwrbseal.cmp BRANCH MODEL: c:\asp\19B9\salem2 .sll PROBABILITY FILE: c:\asp\19B9\pwrbsll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System qon-Recov Opr Fail TRANS 9.OE-04 > 9.OE-D4 L.OE+OO > 1.OE-Ol Event Identifier: 311/90-005
B-237 Branch Model: INITOR Initiator Freq: 9.02-04 loop 1.6E-05 5.3E-01 loca 2.42-06 4.3E-01 2.8E-04 1.2E-01 rt/loop 0.02+00 1.02+00 emerg.power 7.5E-03 8.02-01 afw 3.8E-04 2. 6E-01 afw/emerg.power 5.02-02 3. 4E-01 mfw 1.02+00 7.02E-02 porv.or.srv.chall 4.02-02 1.02+00 porv.or.srv. reseat 2.02-02 1. 1E-02 porv.or.srv. reseat/emerg.power 2.02-02 1.02+00 seal.loca 2.72-01 1. 02+00 ep. rec (si) 5.7E-01 1. 02+00 ep. rec 7.02-02 1. 02+00 HP' 1.02-03 > 1. 02+00 8. 4E-01 Branch Model: 1.OF.2 Train 1 Cond Prob: 1.02-02 > Failed Train 2 Cond Prob: 1.02-01 > Failed HPI (F/B) 1.02-03 > 1.02E+00 8. 4E-01 1. 02-02 Branch Model: 1.OF.2+opr Train 1 Cond Prob: 1.02-02 > Failed Train 2 Cond Prob: 1.02-01 > Failed hpr/-hpi 1.5E-04 1.02E+00 1.02E-03 porv.open 1.02-02 1.02+00 4. 02-04
- branch model file
- forced Mina rick 08-06-1991 17:30:27 Event Identifier: 311/90-005