ML20147A362
| ML20147A362 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-054-00 | |
| Download: ML20147A362 (5) | |
Text
B.29-1 B.29 LER No. 325/82-054 Event
Description:
Scram with RCIC Inoperable Date of Event:
June 7, 1982 Plant:
Brunswick I B.29.1 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 the event is 1.4 x 10'.
B.29.2 Event Description On June 7, 1982, a blown main steam isolation valve (MSIV) fuse caused 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 due to a failed electronic governor module.
B.29.3 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.29.4 Modeling Assumptions The HPCI and RCIC low-level auto-start setpoint is assumed to be the same as the reactor isolation setpoint, so the power conversion and main feedwater systems were assumed to be unavailable. This event was modeled as a scram and isolation, with RCIC unavailable and not recoverable. The long-term nonrecovery probability for the power conversion system (PCS) was revised to 0.017 to reflect the apparent isolation (see Appendix A). Combining this value with the estimated long-term residual heat removal (RHR) nonrecovery probability of 0.016 results in a combined nonrecovery probability for RHR and PCS of 2.7 x 10-4.
B.29.5 Analysis Results The conditional core damage probability estimated for this event is 1.4 x 10'. The dominant core damage sequence, highlighted on the event tree in Figure B.29.1, involves the observed scram, failure of the power LER No. 325/82-054
B.29-2 conversion system, main feedwater recovery, and RHR failure. The RCIC failure does not affect this sequence.
LER No. 325/82-054
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B.29-3
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Figure B.29.1 Dominant core damage sequence for LER 325/82-054 LER No. 325/82-054
B.29-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
Event
Description:
Event Date:
Plant:
325/82-054 Scram with RCIC inoperable June 7. 1982 Brunswick 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS 1.OE+O0 End State/Initiator Probability CD TRANS Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER) 1.4E-05 1.4E-05 Sequence End State Prob 103 105 119 414 413 412 138 trans -rx.shutdown PCS srv.ftc.<2 -MFW RHR.AND.PCS.NREC trans -rx.shutdown PCS srv.ftc.<2 MFW -hpci RHR.AND.PCS.NREC trans -rx.shutdown PCS srv.ftc.<2 MFW hpci RCIC srv.ads c
rd(inj) trans rx.shutdown rpt trans rx.shutdown -rpt slcs trans rx.shutdown -rpt -slcs PCS ads.inhibit trans -rx.shutdown PCS srv.ftc.2 hpci srv.ads CD CD CD CD CD CD CD 6.6E-06 3.3E-06 1.7E-06 6.7E-07 4.1E-07 3.4E-07 3.3E-07 N.Rec**
1.8E-04 9.1E-05 1.7E-01 1.OE-01 1.OE-01 1.OE-01 4.9E-01
rd(inj) trans -rx.shutdown PCS srv.ftc.2 hpci srv.ads trans rx.shutdown -rpt -slcs PCS ads.inhibit trans rx.shutdown -rpt slcs trans rx.shutdown rpt End State Prob CD CD CD CD CD CD CD 6.6E-06 3.3E-06 1.7E-06 3.3E-07 3.4E-07 4.1E-07 6.7E-07 N Rec**
1.8E-04 9.1E-05 1.7E-O1 4.9E-01 1.OE-01 1.OE-01 I.OE-01
- non-recovery credit for edited case SEQUENCE MODEL:
BRANCH MODEL:
c:\\asp\\1982-83\\bwrc8283.cmp c:\\asp\\1982-83\\brunsl.82 LER No. 325/82-054
B.29-5 PROBABILITY FILE:
c:\\asp\\1982-83\\bwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans loop loca rx.shutdown PCS Branch Model:
1.OF.1 Train 1 Cond Prob:
srv.ftc.<2 srv.ftc.2 srv.ftc.>2 MFW Branch Model:
I.OF.1 Train 1 Cond Prob:
hpci RCIC Branch Model:
1.OF.1 Train 1 Cond Prob:
srv.ads crd(inj) cond 1pcs Ipci rhrsw(inj) rhr RHR.AND.PCS.NREC Branch Model:
1.OF.4+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
rhr/-Ipci rhr/lpci rhr(spcool) rhr(spcool)/-lpci ep ep.rec rpt slcs ads.inhibit man.depress 1.OE-03 1.6E-05 3.3E-06 3.5E-04 1.7E-01 > 1.OE+OO 1.7E-01 > 1.OE+00 1.0E+00 1.3E-03 2.2E-04 4.6E-01 > 1.OE+00 4.6E-01 > 1.OE+OO 2.9E-02 6.0E-02 > 1.OE+00 6.0E-02 > 1.OE+OO 3.7E-03 1.0E-02 1.0E+0O 2.DE-03 1.1E-03 2.OE-02 1.5E-04 1.5E-04 > 1.5E-04 1.OE-02 I.QE-01 3.OE-01 5.OE-01 O.OE+OO 1.OE+00 2.1E-03 2.OE-03 2.9E-03 1.6E-01 1.9E-02 2.OE-03 O.OE+OO 3.7E-03 1.OE+O0 3.6E-01 6.7E-01 1.0E-01 1.OE+O0 1.OE+O0 1.OE+O0 1.OE+O0 3.4E-01 7.OE-O1 7.OE-O1 > 1.OE+O0 7.OE-O1 1.OE+O0 3.4E-01 I.OE+O0 1.OE+O0 1.OE+O0 1.6E-02 8.3E-03 > 2.7E-04 1.OE+O0 1.OE+O0 1.OE+O0 1.OE+O0 8.7E-01 1.OE+O0 1.OE+O0 1.OE+O0 1.OE+O0 1.OE+O0 1.OE-02 1.OE-02 1.OE-03 1.OE-02 1.OE-05 1.OE-05 1.OE-05 iQOE-05 1.OE-03 1.OE-03 1.OE-02 1.OE-02 1.OE-02 branch model file
- forced LER No. 325/82-054