ML20149K376
| ML20149K376 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1983-084-00 | |
| Download: ML20149K376 (5) | |
Text
B.44-1 B.44 LER No. 366/83-084 Event
Description:
Reactor Scram with RHR Loop A Unavailable Date of Event:
August 17, 1983 Plant:
Hatch 2 B.44.1 Summary On August 16, 1983, Hatch 2 experienced a reactor scram. While proceeding to cold shutdown, the A loop heat exchanger outlet valve failed to open. The conditional core damage probability estimated for the event is 1.4 x10"4.
B.44.2 Event Description On August 16, 1983, Hatch 2 experienced a reactor scram on low water level due to a reactor feed pump turbine control signal spike. On August 17, 1983, as the unit was going from hot shutdown to cold shutdown, the residual heat removal system (RHR) A loop heat exchanger outlet valve (2El 1-FO03A) failed to open because of a burned-out motor.
When plant personnel attempted to open 2EI I -FO03A, its position indication was lost and personnel received a "valve overload" alarm. An investigation of the valve revealed that its motor suffered an electrical fault when personnel tried to open the valve.
B.44.3 Additional Event-Related Information The cause of the valve motor fault is unknown; however, a similar incident occurred one month earlier (see the analysis of LERs 366/83-042, -055, and -056). The valve motor was replaced and the torque switch setting was calibrated. The valve was returned to service on August 10, 1983.
B.44.4 Modeling Assumptions This event was modeled as a reactor scram with one train of RHR unavailable. The ASP model assumes the dominant failure mode is a common cause failure of the RHR pumps. The potential for common cause failure exists even when a component is failed. Therefore, the conditional probability of a common cause failure was included in the analysis for those components that failed as part of the event. To address the failure of the heat exchanger outlet valve, the model was modified. Failure of the heat exchanger outlet valve disables all functions of a complete train of RHR. For this analysis, one train of RHR (all modes) was assumed failed.
The probability of the second train failing, given failure of the first train, was assumed to be 0.1.
LER No. 366/83-084
B.44-2 B.44.5 Analysis Results The conditional core damage probability estimated for this event is 1.4 xl O4. The dominant core damage sequence, highlighted on the event tree in Figure B.44. l, involves the observed transient, failure of the power conversion system, main feedwater system success, and failure of the RHR system.
LER No. 366/83-084
Cn z
(-C cc 0
z0 (n
>0 C,
C-,
U)
CC0 U,
cc B.44-3 000000000000000000 0000 000 0000 00000 0000 Figure B.44.1 Dominant core damage sequence for LER 366/83-084 LER No. 366/83-084
B.44-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
Event
Description:
Event Date:
Plant:
366/83-084 Scram with RHR loop A unavailable August 17. 1983 Hatch 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)
Sequence 1.4E-04 1.4E-04 End State Prob N Rec**
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
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence 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 CD CD 1.2E-04 7.3E-03 2.2E-05 2.8E-03 End State Prob N Rec**
CD CD 1.2E-04 7.3E-03 2.2E-05 2.8E-03
- non-recovery credit for edited case SEQUENCE MODEL:
BRANCH MODEL:
PROBABILITY FILE:
c:\\asp\\1982-83\\bwrc8283.cmp c:\\asp\\1982-83\\hatch2.82 c:\\asp\\1982-83\\bwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch trans loop 1
oca rx.shutdown System 1.5E-03 1.6E-05 3.3E-06 3.5E-04 Non-Recov
- 1.
OE+OD 3.6E-01 6.7E-01 iDOE-01 Opr Fail LER No. 366/83-084
B.44-5 pcs srv. ftc. <2 srv.ftc.2 srv.ftc.>2 1.7E-01 1.OE+0O 1.3E-03
- 2. 2E-04 mfw hpci rci c srv.ads crd(inj) cond I pcs I pci rhrsw(inj)
RHR Branch Model:
1.OF.4+opr Train I 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 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
Serial Component Prob:
RHR(SPCOOL)/-LPCI Branch Model:
1.OF.1+ser+opr Train 1 Cond Prob:
Serial Component Prob:
ep ep.rec rpt slcs ads.inhibit man.depress 4.6E-01 2.9E-02 6.OE-02 3.7E-03 1.OE-02 1.OE+00 2.OE-03 1.1E-03 2.OE-02 1.5E-04 > 1.0E-01 **
1.0E-02 I.0E-01 3.0E-01 5.OE-01 1.5E-04 > 1.E-01 **
LOE-02 1.OE-01 3.0E-01 5.0E-01 O.OE+O0
> 1CE-01 **
O.OE+O0 1.0E+O0 2.1E-03 > 1.E-01 **
1.OE-02 1.E-01 3.OE-01 5.0E-01 2.0E-03 2.0E-03 > i.CE-01 **
O.OE+C0 2.0E-03 2.9E-03 1.6E-01 1.9E-02 2.0E-03 O.OE+O0 3.7E-03 1.OE+O0 1.0E+O0 1.OE+O0 1.OE+O0 3.4E-01 7.0E -01 7 CE-01 7.0E-01 1.0E+O0 3.4E-01 1.0E+O0 1.0E+O0 1.0E+O0 1.6E-02 8.3E-03 l.OE+0O 1.0E+O0 1.0E+O0 1.0E+O0
- 8. 7E- 01 1.0OE+O0 1 ý0E+O0
- 1. OE+ 00 1.0E+O0 1.0OE+O0 1.0E-02 1.OE-02 1.0E-03 I.OE-02 i.0E-05 1.0E-05 1.OE-05 1.0E-05 L.0E-03 1.OE-03 1.0E-02 1.0E-02 1.0E-02 branch model file
- forced LER No. 366/83-084