ML20147A471
| ML20147A471 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter Office of Nuclear Regulatory Research |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-005-00 | |
| Download: ML20147A471 (6) | |
Text
B.24-1 B.24 LER No. 324/82-005 Event
Description:
Scram with both RHRSW Loops Inoperable Date of Event:
January 16, 1982 Plant:
Brunswick 2 B.24.1 Summary After a reactor scram, operators attempted to align suppression pool cooling but were unable to do so because both residual heat removal (RHR) system service water (SW) loops were found to be inoperable. The conditional core damage probability estimated for the event is 2.3 x 10-4.
B.24.2 Event Description On January 16, 1982, Brunswick 2 experienced a scram due to low condenser vacuum. After the scram, a group I isolation occurred and the main steam isolation valves (MSIVs) closed. Operators aligned the reactor core isolation cooling system (RCIC) to supply makeup water to the reactor. Later, when operators attempted to align suppression pool cooling, they discovered that both RHRSW loops were inoperable. Low suction header pressure lockout signals prevented start of pumps in both loops. Operators reset the group I isolation, reopened the MSIVs, re-established condenser vacuum, and realigned the main feedwater power conversion system (PCS) for makeup and decay heat removal.
An inspection of the suction header pressure switches found that their sensing lines were partially plugged with sediment, which may have prevented the switches from sensing the actual header pressure, which was within acceptable limits. The suction header pressure switch for the A loop was also found to be damaged.
In addition, the power supply of the B loop suction header pressure switch was found to be switched off, apparently having been left that way after prior maintenance work. The pressure switch power feed breaker was reclosed, the RHRSW B loop interlock cleared, and the associated RHR train was started and aligned for suppression pool cooling. RHRSW train B was tested and declared operable approximately 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after the scram. The A service water loop was made operable approximately 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> after the scram.
B.24.3 Additional Event-Related Information "Operating Experience Feedback Report - Service Water System Failures and Degradations," NUREG-1275, V. 3, and "Brunswick Nuclear Power Station Unit 2 Loss of Residual Heat Removal Service Water on January 16, 1982," AEOD/Engineering Evaluation Report E236, USNRC, provide additional detail about this event.
B.24.4 Modeling Assumptions This event was modeled as a scram with both trains of RHRSW initially unavailable. The RHRSW pumps at Brunswick maintain a positive pressure differential between the tube and shell side of the RHR heat LER No. 324/82-005
B.24-2 exchangers, which prevents leakage of primary coolant into the service water (SW) system. Adequate decay heat removal can be provided in the event of RHRSW pump unavailability using the SW pumps to directly supply the RHR heat exchangers, if one valve (FO68A/B) in each train is locally opened. This action is addressed in the Brunswick IPE, and an operator failure probability of 0.01 was estimated. Because of the unavailability of the RHRSW trains, all modes of RHR, except low-pressure coolant injection (LPCI), were modeled as initially failed.
As this event involved a loss of condenser vacuum and MSIV isolation, the power conversion system was assumed to be failed and nonrecoverable in the short term (PCS was assumed to be recoverable in the long term).
To recover decay heat removal capability using RHR, operators needed to either recover the inoperable RHRSW pumps or align the service water system to supply the RHR heat exchangers. In the event, since the PCS had been recovered and was being used for decay heat removal, the operators focused on correcting the RHRSW suction header pressure switch problems and restoring RHRSW.
If the PCS had not been recovered, RHR could have been recovered by locally opening SW valves F068A and B.
To address this action, 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 0.017 [probability of not aligning SW multiplied by PCS long-term noikrecovery given MSIV closure (see Appendix A)], or 1.7E-4.
B.24.5 Analysis Results The conditional core damage probability estimated for this event is 2.3 x 10'. The dominant core damage sequence, highlighted on the event tree in Figure B.24. 1, involves the observed scram, failure of the power conversion system, and RHR failure.
LER No. 324/82-005
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Figure B.24.1 Dominant core damage sequence for LER 324/82-005 LER No. 324/82-005
B.24-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
Event
Description:
Event Date:
Plant:
324/82-005 Scram with both RHRSW loops inoperable January 16. 1982 Brunswick 2 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) 2.3E-04 2.3E-04 Sequence End State Prob 103 trans -rx.shutdown PCS srv.ftc.<2 -MFW RHR.AND.PCS.NREC 105 trans -rx.shutdown PCS srv.ftc.<2 MFW -hpci RHR.AND.PCS.NREC 403 trans rx.shutdown -rpt -slcs PCS -ads.inhibit -hpci RHR(SPCOO L) 121 trans.-rx.shutdown PCS srv.ftc.2 -hpci -cond RHR 123 trans -rx.shutdown PCS srv.ftc.2 -hpci cond -Ipcs RHR CD CD CD CD CD 1.2E-04 6.OE-05 3.3E-05 N Rec**
1.1E-04 5.7E-05 9.9E-02 8.4E-06 6.6E-03 4.3E-06 3.4E-03
-* non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob 103 105 121 123 403 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 -hpci -cond RHR trans -rx.shutdown PCS srv.ftc.2 -hpci cond -Ipcs RHR trans rx.shutdown -rpt -slcs PCS -ads.inhibit -hpci RHR(SPCOO L)
CD CD CD CD CD 1.2E-04
- 6.
OE-05 8.4E-06 4.3E- 06 3.3E-05 N Rec**
1.1E-04 5.7E-05 6.6E-03 3.4E-03 9.9E-02
- non-recovery credit for edited case SEQUENCE MODEL:
BRANCH MODEL:
PROBABILITY FILE:
No Recovery Limit c:\\asp\\1982-83\\bwrc8283.cmp c:\\asp\\1982-83\\bruns2.82 c:\\asp\\1982-83\\bwr8283.pro L_
I LER No. 324/82-005
B.24-5 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:
1.OF.1 Train 1 Cond Prob:
hpci rcic srv.ads crd(inj) cond 1pcs 1pci RHRSW(INJ)
Branch Model:
1.OF.l+opr Train 1 Cond Prob:
RHR Branch Model:
1.OF.4+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
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/-LPCI Branch Model:
1.OF.l+opr Train I Cond Prob:
rhr/lpci RHR(SPCOOL)
Branch Model:
1.OF.4+ser+opr Train I Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
Serial Component Prob:
RHR(SPCOOL)/-LPCI Branch Model:
1.OF.l+ser+opr Train 1 Cond Prob:
Serial Component Prob:
ep ep.rec rpt 1.1E-03 1.6E-05 3.3E-06 3.5E-04 1.7E-01 > 1.OE+OO 1.7E-01 > 1.OE+00 1.OE+OO 1.3E-03 2,2E-04 4.6E-01 > 1.OE+OO 4.6E-01 > 1.OE+OO 2.9E-02 6.OE-02 3.7E-03 1.OE-02 1.OE+OO 2.OE-03 1.1E-03 2.OE-02 > 1.OE+OO 2.OE-02 > 1.OE+OO 1.5E-04 > 1.OE+OO
- 1.OE-02 i.QE-Ol 3.OE-01 5.0E-01 1.5E-04 > 1.OE+OO
- 1.OE-02 iQOE-Ol 3.OE-O1 5.OE-01 O.OE+OQ > 1.OE+OO
- O.QE+OO 1.OE+0O 2.1E-03 > 1.OE+OO
- 1.OE-02 i.OE-0l 3.OE-O1 5.OE-O1 2.OE-03 2.QE-03 >1.OE÷QO
- O.OE+OO 2.OE-03 2.9E-03 1.6E-01 1.9E-02
- 1.
OE+OO 3.6E-01 6.7E-01 1i0E-01
- 1.
OE+OO 1.0E+00
- 1.
OE+OO 1.OE+OO 3.4E-01 7.OE-01 7.OE-O1 7.OE-01
- 1.
OE+0O 3.4E-O01
- 1.
OE+OO 1.OE+OO
- 1.
QE+0O 1.6E-02 > 1.OE-02 8.3E-03 > 1.7E-04 1.OE+OO 1.OE+00 1.OE+0O 1.QE+00 8.7E-01 1.OE+OO 1.OE+OO 1.OE-02 1.OE-02 1.OE-03 1.OE-02 i.QE-OS 1.OE-05 1.OE-05 i.QE-05 1.OE-03
- 1.
OE- 03 LER No. 324/82-005
B.24-6 slcs 2.OE-03 1.OE+O0 1.OE-02 ads.inhibit O.OE+O0 1.OE+O0 1.OE-02 man.depress 3.7E-03 1.OE+O0 1.OE-02
- branch model file
- forced LER No. 324/82-005