ML20147A361
| ML20147A361 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-041-00 | |
| Download: ML20147A361 (6) | |
Text
B.28-1 B.28 LER No. 325/82-041 Event
Description:
Both RHRSW Loops Simultaneously Inoperable Date of Event: March 25, 1982 Plant: Brunswick I B.28.1 Summary Loop B of the residual heat removal (RHR) service water (SW) system was found to be inoperable during a period when loop A was tagged out for maintenance. The estimated increase in core damage probability, or importance, over the duration of the event is 4.7 x I10. The base-case core damage probability (CDP) over the duration of the event is 2.9 x 10"7, resulting in an estimated conditional core damage probability (CCDP) of 4.7 x 10'.
B.28.2 Event Description During power operations, an auxiliary operator discovered that the motor cooler isolation valves to 1B and ID pumps were open with the pumps not running. Investigating, he found that the breaker which supplied the motor cooler isolation valves had tripped, de-energizing the valves as well as the B loop RHRSW low-suction header pressure switches. In turn, this rendered the B loop of RHRSW inoperable. At the same time, loop A RHRSW was tagged out for maintenance.
B.28.3 Additional Event-Related Information Loop B of RHRSW had been flushed approximately two days prior to the event, which entailed manipulation of the breaker in question.
B.28.4 Modeling Assumptions It was assumed that RHRSW loop B was unavailable from the time of the system flush until discovery of the mispositioned breaker. Loop A was assumed to have been unavailable throughout this period as well. This event was modeled as a two-day unavailability of RHRSW and, accordingly, of RHR. The RHRSW pumps at Brunswick maintain a positive pressure differential between the tube and shell side of the RHR heat exchangers, which prevents primary coolant leakage into the service water (SW) system. Adequate decay heat removal can be provided using the SW pump if valves F068A and B are locally opened. This action is addressed in the Brunswick individual plant examination (IPE), and an operator error probability of 0.01 was estimated. To address this section, the nonrecovery probability for RHR was revised to 0.01 to reflect the probability of the operators failing to open F068A and B. For sequences involving potential RHR and PCS recovery, the nonrecovery estimate was revised to 0.01 x 0.52 (see Appendix A), or 5.2 x 10'.
LER No. 325/82-041
B.28-2 B.28.5 Analysis Results The estimated increase in core damage probability over the duration of the event is 4.7 x 10'. The base-case CDP (not shown in calculation) is 2.9 x 107, resulting in an estimated CCDP of 4.7 x 10W. The dominant core damage sequence, highlighted on the event tree in Figure B.28. 1, involves a transient with failure of the power conversion system, main feedwater success, and RHR failure.
LER No. 325/82-041
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B.28-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 325/82-041 Event
Description:
Both RHRSW loops simultaneously inoperable Event Date: March 25. 1982 Plant: Brunswick I UNAVAILABILITY. DURATION= 48 NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 5.OE-02 LOOP 2.BE -04 LOCA 1.IE-04 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 4.4E-05 LOOP 2.8E-06 LOCA 1.8E-07 Total 4.7E-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 3.7E-05 4.6E-03 105 trans -rx.shutdown pcs srv.ftc.<2 mfw -hpci RHR.AND.PCS.NREC CD 6.6E-06 1.8E-03 202 loop -rx.shutdown -ep srv.ftc.<2 -hpci RHR CD 2.7E-06 3.6E-03
- 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 3.7E-05 4.6E-03 105 trans -rx.shutdown pcs srv.ftc.<2 mfw -hpci RHR.AND.PCS.NREC CD 6.6E-06 1.8E-03 202 loop -rx.shutdown -ep srv.ftc.<2 -hpci RHR CD 2.7E-06 3.6E-03
- 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 MODEL: c:\asp\1982-83\bwrc8283.cmp BRANCH MODEL: c:\asp\1982-83\brunsl.82 PROBABILITY FILE: c:\asp\1982-83\bwr8283.pro LER No. 325/82-041
B.28-5 No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 1.OE-03 1.OE+OO loop 1.6E-05 3.6E-01 loca 3.3E-06 6.7E-01 rx. shutdown 3.5E-04 1.0E-01 pcs 1.7E-01 1.OE+0O srv.ftc.<2 1.OE+00 1.OE+00 srv.ftc.2 1.3E-03 1.OE+OO srv.ftc.>2 2.2E-04 1.OE+OO mfw 4.6E-01 3.4E- 01 hpci 2.9E-02 7.OE-01 rcic 6.OE-02 7.OE-01 srv.ads 3.7E-03 7.OE-01 1.OE-02 crd(inj) 1.OE-02 1.OE+00 1.OE-02 cond 1.OE+OO 3.4E-01 1.OE-03 Ipcs 2.OE-03 1.OE+00 1pci 1.1IE-03 1.OE+OO RHRSW(INJ) 2.OE-02 >1.OE+OO 1.OE+00 1.OE-02 Branch Model: 1.OF.l+opr Train 1 Cond Prob: 2.OE-02 > 1.OE+OO RHR 1.5E-04 > 1.OE+0O 1.6E-02 > 1.OE-02 1.OE-05 Branch Model: 1.OF.4+opr Train 1 Cond Prob: 1.OE-02> 1.0E+00 Train 2 Cond Prob: 1.OE-01> 1.OE+OO Train 3 Cond Prob: 3.0E -O01>1.OE+OO Train 4 Cond Prob: 5. E-01 1.OE+OO RHR.AND.PCS.NREC 1.5E-04> 1.OE+00 8.3E-03 > 5.2E-03 1.OE-05 Branch Model: 1.OF.4÷opr Train 1 Cond Prob: 1.OE-02> 1.OE+0O Train 2 Cond Prob: 1.OE-O1> 1.OE+0O Train 3 Cond Prob: 3.OE -01> 1.OE+0O Train 4 Cond Prob: 5.OE -01> 1.OE+00 RHR/-LPCI O.OE+OO I .OE+OO 1.OE+OO > 1.OE-02 1.OE-05 Branch Model: 1.OF.l+opr Train 1 Cond Prob: O.OE+OO > 1.OE+OO rhr/lpci 1.OE+0O 1.OE+OO 1.OE-05 RHR(SPCOOL) 2.1E-03 > 1.OE+OO 1.0E+00 1.OE-03 Branch Model: 1.OF.4+ser+opr Train 1 Cond Prob: 1.OE-02 > 1.OE+OO Train 2 Cond Prob: iQOE-0l > 1.OE+00 Train 3 Cond Prob: 3.OE-O1 > 1.OED0O Train 4 Cond Prob: 5.OE-O1 > 1.OE+00 Serial Component Prob: 2.OE-03 RHR(SPCOOL)/-LPCI 2.OE-03 > 1.OE+OD 1.OE+0O 1.QE-03 Branch Model: 1.OF.l+ser+opr Train 1 Cond Prob: O.OE+OO 1.OE+00 Serial Component Prob: 2.OE-03 ep 2.9E-03 8.7E-01 ep. rec 1.6E-01 1.OE+00 rpt 1.9E-02 1.OE+0O slcs 2.OE-03 1.OE+OO 1.OE-02 ads.inhibit O.OE+00 1.OE+00 1.OE-02 LER No. 325/82-041
B.28-6 man.depress 3.7E-03 1.OE+O0 1.OE-02
- branch model file
- forced LER No. 325/82-041