ML20149K397
| ML20149K397 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1983-117-00, LER 1983-147-00 | |
| Download: ML20149K397 (5) | |
Text
B.48-1 B.48 LER No. 373/83-117, -147 Event
Description:
B RHR Heat Exchanger Outlet Valve Failure Date of Event: September 30, 1983 Plant: LaSalle 1 B.48.1 Summary Both licensee event reports indicate that the B train residual heat removal (RHR) heat exchanger outlet valve failed to open on demand, due to hydraulic locking. Manual attempts to open the valve were unsuccessful on both occasions. A reactor scram occurred on November 3, during the time that the B train of RHR was potentially unavailable. The conditional core damage probability estimated for this event is 1.4 x 10'.
B.48.2 Event Description On September 20, 1983, while LaSalle 1 was in cold shutdown, operators at LaSalle attempted to open the B RHR heat exchanger outlet valve, but were unable to do so. Attempts using the valve motor operator and manual attempts were both unsuccessful. Subsequent inspection determined that the valve was experiencing hydraulic locking when water became trapped in the bonnet cavity. Since the bonnet cavity did not have any means to vent off water trapped within, the valve could become locked in the closed position. Licensee event report 373/83-117 indicates that the problem was recurring.
After the event, the motor operator for the valve was inspected. The motor windings were found to be burned and the motor was replaced. A plan was then formulated to check the performance of the valve over the next two complete shutdowns before making a permanent fix.
On November 12, 1983, a few days after a scram, operators attempted to open the B RHR heat exchanger outlet valve but, again, were unable to do so. The licensee event report for this event, 373/83-147, refers to the test plan of the prior event but does not make it clear if this was the first or second complete shutdown.
Again, the cause of the valve failure was found to be hydraulic locking. The valve motor operator was again found to be burned, and the motor was replaced.
B.48.3 Additional Event-Related Information None.
B.48.4 Modeling Assumptions This event was modeled as a scram with the B RHR heat exchanger assumed inoperable. Train B of RHR was assumed to be inoperable for all modes requiring RHR service water (SW) cooling. Although the specific LER No. 373/83-117, -147
B.48-2 failure discovered was not reported to be present in redundant portions of the system, other potential common cause failure modes remained and could have affected system performance. 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 were assumed to have been failed as a part of the postulated event.
The plant power conversion system was assumed to have remained available but vulnerable to failure during this event.
It would also have been appropriate to have modeled the period that the B RHR heat exchanger was unavailable, thereby analyzing the risk impact of potential initiators which could have occurred. However, while the problems with the B train RHR heat exchanger outlet valve were recurring and apparently existed during much of 1983, limited information was available concerning other failures and plant operating history during that time. Therefore, the unavailability was not modeled.
B.48.5 Analysis Results The conditional core damage probability estimated for this event is 1.4 x 10-4. The dominant core damage sequence for this event, highlighted on the event tree in Figure B.48.1, involves scram, failure of the power conversion system, main feedwater success and RHR failure.
LER No. 373/83-117, -147
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B.48-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 373/83-117 Event
Description:
B RHR heat exchanger outlet valve failure Event Date: September 30. 1983 Plant: LaSalle I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OE+O0 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 1.4E-04 Total 1.4E-041 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 1.3E-04 7.7E-03 105 trans -rx.shutdown pcs srv.ftc.<2 mfw -hpci RHR.AND.PCS.NREC CD 1.4E-05 2.8E-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 1.3E-04 7.7E-03 105 trans -rx.shutdown pcs srv.ftc.<2 mfw -hpci RHR.AND.PCS.NREC CD 1.4E-05 2.8E-03
- non-recovery credit for edited case SEQUENCE MODEL: d:\asp\models\bwrc8283.cmp BRANCH MODEL: d:\asp\models\lasallel.82 PROBABILITY FILE: d:\asp\models\bwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES LER No. 373/83-117, -147
B.48-5 Branch System Non- Recov Opr Fail trans 1.5E-03 1.OE+OO loop 1.6E-05 5.3E-01 1oca 3.3E-06 6,7E-01 rx.shutdown 3.5E-04 1.OE-01 pcs 1.7E-01 1.OE+OO srv.ftc.<2 1.OE+O0 1.OE+OO srv.ftc.2 1.3E-03 1.0E--00 srv.ftc.>2 2.2E-04 1.OE+00 mfw 2.9E-01 3.4E-01 hpci 2.OE-02 3.4E-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+O0 3.4E-01 1.OE-03 1pcs 2.0E-02 1.OE+00 1pci 6.OE-04 1.OE+O0 rhrsw(inj) 2.OE-02 1.OE+0O 1.OE-02 RHR 1.OE-03 > 1.OE-01 1.6E-02 1.OE-05 Branch Model: 1.OF.2+opr Train 1 Cond Prob: 1.OE-02 > 1.OE+O0 Train 2 Cond Prob: LOE-01 RHR.AND.PCS.NREC 1LOE-03 > 1.OE-01 8.3E-03 1.OE-05 Branch Model: 1.OF.2+opr Train 1 Cond Prob: 1.OE-02 > 1.OE+O0 Train 2 Cond Prob: 1GE-01 RHR/-LPCI O.OE+O0 > 1.0E-01 ** 1.OE+00 1.OE-05 Branch Model: 1.OF.l+opr Train 1 Cond Prob: O.OE+O0 rhr/lpci 1.OE+O0 1.OE+O0 1.OE-05 RHR(SPCOOL) 2.OE-03 > 1.0E-01 1.OE+00 1.OE-03 Branch Model: 1.OF.2+opr Train 1 Cond Prob: 2.OE-02 > 1.OE+O0 Train 2 Cond Prob: 1.OE-01 RHR(SPCOOL)/-LPCI 1.OE-03 > 1OE-01 1.OE+00 1.OE-03 Branch Model: 1.OF.2+opr Train 1 Cond Prob: 1.OE-02 > 1.OE+O0 Train 2 Cond Prob: 1.OE-O1 ep 2.9E-03 8.7E-01 ep.rec 1.7E-01 1.OE+00 rpt 1.9E-02 1.OF+00 slcs 2.OE-03 1.OE+00 1.OE-02 ads.inhibit O.OE+O0 1.OE+00 1.OE-02 man.depress 3.7E-03 1.OE+00 L.OE-02
- branch model file
- forced LER No. 373/83-117, -147