ML20147A360
| ML20147A360 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-025-00 | |
| Download: ML20147A360 (5) | |
Text
B.27-1 B.27 LER No. 325/82-025 Event
Description:
Scram with RCIC Inoperable Date of Event: February 18, 1982 Plant: Brunswick I B.27.1 Summary After a reactor scram, the reactor core isolation cooling (RCIC) system and high-pressure coolant injection (HPCI) systems were signalled to start by a low reactor water level. A failure of the turbine speed controller caused RCIC to immediately trip, however. The conditional core damage probability estimated for this event is 1.3 x 10".
B.27.2 Event Description On February 18, 1982, Brunswick 1 experienced a scram, followed by a low reactor water level start signal for HPCI and RCIC. While HPCI apparently performed normally, RCIC started and immediately tripped on high exhaust pressure. This was attributed to an improperly calibrated turbine speed control system. RCIC was successfully restarted and operated manually to provide reactor vessel makeup.
B.27.3 Additional Event-Related Information Following a similar event described in LER 325/82-069, the RCIC control system problems were eventually attributed to a control system design error. The RCIC electronic governor module was found not to have a reference signal common to the RCIC speed controller. Accordingly, variations between the two circuits in sensed ground potential caused unpredictable control system behavior. The flawed control system design apparently had existed since plant startup.
B.27.4 Modeling Assumptions This event was modeled as a scram, with RCIC assumed unavailable, but recoverable. As reactor vessel level dropped to the auto-start setpoint for RCIC and HPCI, the reactor was assumed to have isolated. This isolation resulted in the unavailability of the power conversion and feedwater systems. The nonrecovery probability for the power conversion system (PCS) was revised to 0.017 to reflect the main steam isolation valve (MSIV) closure (see Appendix A). Combining this value with the estimated long-term RHR nonrecovery probability of 0.016 results in a combined nonrecovery probability for residual heat removal (RHR) and PCS of 2.7E-4.
LER No. 325/82-025
B.27-2 B.27.5 Analysis Results The conditional core damage probability estimated for this event is 1.3 x 10'. The dominant core damage sequence, highlighted on the event tree in Figure B.27. 1, involves the observed scram and failure of the power conversion system and RHR.
LER No. 325/82-025
B.27-3 0-WO U) z 00000 000000000000000000000000000U 000O000Y00o0u Cr z
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Figure B.27.1 Dominant core damage sequence for LER 325/82-025 LER No. 325/82-025
B.27-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 325/82-025 Event
Description:
Scram with RCIC inoperable Event Date: February 18. 1982 Plant: Brunswick 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 1.3E-05 Total 1.3E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
103 trans -rx.shutdown PCS srv.ftc.<2 -MFW RHR.AND.PCS.NREC CD 6.6E-06 1.8E-04 105 trans -rx.shutdown PCS srv.ftc.<2 MFW-hpci RHR.AND.PCS.NREC CD 3.3E-06 9.1E-05 119 trans -rx.shutdown PCS srv.ftc.<2 MFW hpci RCIC srv.ads c CD 1.2E-06 1.2E-01 rd(inj) 414 trans rx.shutdown rpt CD 6.7E-07 1.0E-01 413 trans rx.shutdown -rpt slcs CD 4.1E-07 1.OE-01 412 trans rx.shutdown -rpt -slcs PCS ads.inhibit CD 3.4E-07 1.0E-01 138 trans -rx.shutdown PCS srv.ftc.2 hpci srv.ads CD 3.3E-07 4.9E-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.AND.PCS.NREC CD 6.6E-06 1.8E-04 105 trans -rx.shutdown PCS srv.ftc.<2 MFW-hpci RHR.AND.PCS.NREC CD 3.3E-06 9.1E-05 119 trans -rx.shutdown PCS srv.ftc.<2 MFW hpci RCIC srv.ads c CD 1.2E-06 1.2E-01 rd(inj) 138 trans -rx.shutdown PCS srv.ftc.2 hpci srv.ads CD 3.3E-07 4.9E-01 412 trans rx.shutdown -rpt -slcs PCS ads.inhibit CD 3.4E-07 1.0E-01 413 trans rx.shutdown -rpt slcs CO 4.1E-07 1.DE-01 414 trans rx.shutdown rpt CD 6.7E-07 i.0E-01
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\1982-83\bwrc8283.cmp LER No. 325/82-025
B.27-5 BRANCH MODEL: c:\asp\1982-83\brunsl.82 PROBABILITY FILE: c:\asp\1982-83\bwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 1.OE-03 1.OE+00 loop 1.6E-05 3.6E -01 1oca 3.3E-06 6.7E-01 rx.shutdown 3.5E-04 iDOE-0l PCS 1.7E-01 > 1.OE+00 1.OE+00 Branch Model: I.OF.1 Train 1 Cond Prob: 1.7E-01 > 1.OE+O0 srv.ftc.<2 1.OE+O0 1.OE+00 srv.ftc.2 1.3E-03 1.OE+00 srv.ftc.>2 2.2E-04 1.OE+00 MFW 4.6E-01 > 1.OE+00 3.4E-01 Branch Model: I.OF.1 Train 1 Cond Prob: 4.6E-01 > 1.OE+O0 hpci 2.9E-02 7.OE-O01 RCIC 6.OE-02 > 1.OE+O0 7.OE- 01 Branch Model: 1.OF.I Train 1 Cond Prob: 6.OE-02 > 1.OE+O0 srv.ads 3.7E-03 7.OE- 01 1.OE-02 crd(inj) 1.OE-02 1.OE+00 I.OE-02 cond 1.OE+O0 3.4E-01 IOE-03 1pcs 2.OE-03 1.OE+00 1pci 1.1E-03 1.0E+00 rhrsw(inj) 2.OE-02 1.OE+00 1.OE-02 rhr 1.5E-04 1.6E-02 I.OE-05 RHR.AND.PCS.NREC 1.5E-04 > 1.5E-04 8.3E-03 > 2.7E-04 I.OE-05 Branch Model: 1.OF.4+opr Train 1 Cond Prob: I.OE-02 Train 2 Cond Prob: I.OE-01 Train 3 Cond Prob: 3.0E-O1 Train 4 Cond Prob: 5.OE-O1 rhr/-lpci O.OE+O0 1.0E+00 I.OE-05 rhr/lpci 1.OE+00 1.OE+00 1.OE-05 rhr(spcool) 2.1E-03 1.OE+00 1.OE-03 rhr(spcool)/-Ipci 2.OE-03 1.OE+00 1.OE-03 ep 2.9E-03 8.7E-01 ep.rec 1.6E-O1 1.OE+00 rpt 1.9E-02 1.OE+00 slcs 2.OE-03 1.OE+00 1.OE-02 ads.inhibit O.OE+O0 1.OE+OO 1.OE-02 man.depress 3.7E-03 1.OE+00 1.OE-02
- branch model file
- forced LER No. 325/82-025