ML20156A132
| ML20156A132 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-023-00, LER 1982-024-00 | |
| Download: ML20156A132 (5) | |
Text
B.15-1 B.15 LER No. 293/82-024 and -023 Event
Description:
Scram and HPCI Failure Date of Event: August 13, 1982 Plant: Pilgrim B.15.1 Summary During recovery from a scram on August 13, 1982 (LER 293/82-023), the high-pressure coolant injection (HPCI) system tripped after 5 minutes owing to high reactor water level. After restarting the HPCI pump, attempts to bring it past idle speed were unsuccessful. The estimated conditional core damage probability for the event is 2.9 x 105.
B.15.2 Event Description On August 13, 1982, a scram occurred when a removable hand rail fell against main steam hi-flow instrumentation and generated a containment isolation signal (LER 293/82-023). During recovery from the scram, the HPCI system tripped after 5 minutes, owing to high reactor water level. After restarting the HPCI pump, attempts to bring it past idle speed were unsuccessful. Eleven manual safety relief valve (SRV) actuations were required to control pressure. Investigation of the HPCI system revealed that the HPCI gland seal condenser gasket had failed, causing wetting of the HPCI control circuitry. The control circuits were dried and calibrated, and gasket repair was accomplished.
B.15.3 Additional Event-Related Information The HPCI system consists of a single turbine-driven pump that can provide primary coolant makeup at a rate of 4250 gpm. The HPCI pump is provided with two suction sources. The primary source is the condensate storage tank (CST), with the suppression pool providing the secondary source. These are interlocked to ensure that only one source is aligned at a time. The system is designed to swap from the CST to the suppression pool on low CST or high suppression pool level.
B.15.4 Modeling Assumptions This event was modeled as a transient initiator with the power conversion system (PCS) unavailable and HPCI failed due to control circuit wetting and not recoverable. The PCS system was assumed unavailable because a containment isolation signal was generated when the hand rail fell against the main steam hi-flow instrumentation; this signal is expected to have closed the main isolation valves (MSIVs).
The main feedwater system is motor driven at Pilgrim, and was assumed to be available following closure of the MSIVs.
LER No. 293/82-024 and -023
B.15-2 The nonrecovery probability for sequences involving residual heat removal (RHR) or PCS recovery was revised to reflect the MSIV isolation (see Appendix A).
B.15.5 Analysis Results The estimated conditional core damage probability for the event is 2.9 x 10'. The dominant sequence, highlighted on the event tree in Figure B. 15.1, involves a transient initiator followed by successful reactor shutdown, failure of the power conversion system, failure of two SRVs to close, HPCI unavailability and automatic depressurization system (ADS) failure.
LER No. 293/82-024 and -023
B.15-3 a: 000000000800000 0000 00000000O0080000000OU00868 00 cc (z
(0-0.
to a0-cc2z CL
>0 C.)
0 IL U)
Figure B. 15.1 Dominant core damage sequence for LER 293/82-024 and -023 LER No. 293/82-024 and -023
B.15-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 293/82-024 Event
Description:
Scram and HPCI failure Event Date: August 13. 1982 Plant: Pilgrim INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+O0 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 2.9E-05 Total 2.9E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
138 trans -rx.shutdown PCS srv.ftc.2 HPCI srv.ad:sD.PCS.NREC CD 1.6E-05 7.0E-01 103 trans -rx.shutdown PCS srv.ftc.<2 -mfw RHR.AN CD 9.OE-06 2.5E-04 119 trans -rx.shutdown PCS srv.ftc.<2 mfw HPCI rcic srv.ads c CD 1.0E-06 1.7E-01 rd(inj) 107 trans -rx.shutdown PCS srv.ftc.<2 mfw HPCI -i rcic RHR.AND.PC CD 9.5E-07 9.1E-05 S.NREC 414 trans rx.shutdown rpt CD 6.7E-07 i.0E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
103 trans -rx.shutdown PCS srv.ftc.<2 -mfw RHR.AN[ D.PCS.NREC CD 9.0E-06 2.5E-04 107 trans -rx.shutdown PCS srv.ftc.<2 mfw HPCI -rrcic RHR.AND.PC CD 9.5E-07 9.1E-05 S.NREC 119 trans -rx.shutdown PCS srv.ftc.<2 mfw HPCI rcic srv.ads c CD 1.OE-06 1.7E-01 rd(inj) 138 trans -rx.shutdown PCS srv.ftc.2 HPCI srv.ad s CD 1.6E-05 7.0E-01 414 trans rx.shutdown rpt CD 6.7E-07 1.0E-01
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\1982-83\bwrc8283.cmp BRANCH MODEL: c:\asp\19B2-83\pilgrim.82 PROBABILITY FILE: c:\asp\1982-83\bwr8283.pro No Recovery Limit LER No. 293/82-024 and -023
B.15-5 BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 1.2E-03 1.OE+00 1oop 2.0E -05 4.3E-01 1oca 3.3E-06 6.7E-01 rx. shutdown 3.5E-04 iGOE-0l PCS 1.7E-01 >1.0E+00 1.OE+00 Branch Model: 1.OF.1 Train 1 Cond Prob: 1.7E-01 > 1.0E+00 srv.ftc.<2 1.0E+00 1.OE+00 srv.ftc.2 1.3E-03 1.OE'00 srv.ftc.>2 2.2E-04 1.OE+00 mfw 2.9E-01 3.4E-01 HPCI 2.9E-02 > 1.0E+00 7.OE-01 > 1.OE+00 Branch Model: 1.OF.1 Train I Cond Prob: 2.9E-02 > 1.0E+00 rcic 6.OE-02 7.OE-01 srv.ads 3.7E-03 7.OE-01 1.OE-02 crd(inj) 1.0E-02 1.OE+00 1.OE-02 cond 1.0E+00 3.4E-01 1.0E-03 1pcs 2.OE-03 1.0E+00 1pci 1.1E-03 1.OE+00 rhrsw(inj) 2.OE-02 1.OE+00 1.0E-02 rhr 1.5E-04 1.6E-02 iQOE-05 RHR.AND.PCS.NREC 1.5E-04 > 1.5E-04 8.3E-03 > 2.7E-04 1.OE-05 Branch Model: 1. OF. 4+opr Train 1 Cond Prob: 1.0E-02 Train 2 Cond Prob: 1.OE-01 Train 3 Cond Prob: 3.OE-01 Train 4 Cond Prob: 5.OE-01 rhr/-lpci 0.0 E+00 1.0E+00 1.OE-05 rhr/lpci 1.OE+00 1.OE+00 1.OE-05 rhr(spcool) 2.1E-03 1.OE+00 1.0E-03 rhr(spcool)/-lpci 2.OE-03 1.0E+00 1.0E-03 ep 2.9E- 03 8.7E-01 ep.rec 3.1E-02 1.OE+00 rpt 1.9E-02 1.0E-'00 slcs 2.OE-03 1.OE+00 1.OE-02 ads.inhibit 0.0E+00 1.OE+00 1.0E-02 man.depress 3.7E-03 1.OE+00 1.OE-02
- branch model file
- forced LER No. 293/82-024 and -023