ML20156A259
| ML20156A259 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1983-055-00 | |
| Download: ML20156A259 (5) | |
Text
B.13-1 B.13 LER No. 281/83-055 Event
Description:
Trip with AFW Pump Inoperable Date of Event: November 18, 1983 Plant: Surry 2 B.13.1 Summary Auxiliary feedwater (AFW) pump B was found failed due to steam binding on November 18, 1983. On November 20, 1982, it was found failed due to a failed lube oil cooler. Surry 2 experienced a trip on November 16. The conditional core damage probability estimated for this event is 3.5 x 10'.
B.13.2 Event Description Surry unit 2 was operating at full power on November 18, 1983, when the B motor-driven AFW pump failed to provide flow when started. An investigation determined that a leaking check valve was allowing backflow into the pump, which became steam bound. A similar problem was experienced by the pump on December 6, 1983. The turbine-driven AFW pump at Surry experienced a steam-binding problem on November 20; however, the relevant licensee event report indicates that the pump had been operable previously. In addition, AFW pump B was found to have a failed lube oil cooler during maintenance efforts on November 20. There was a reactor trip reported on November 16, 1983.
B.13.3 Additional Event-Related Information None.
B.13.4 Modeling Assumptions As the problems with motor-driven auxiliary feedwater pump (MDAFWP) B reported on November 18 and 20 were believed to have been latent during the trip on November 16, this event was modeled as a trip with that AFW pump inoperable. It was assumed that failure of the other AFW pumps from the same cause was possible. Although the specific failure discovered was not reported to be present in redundant systems, the potential for common cause failure was believed to exist. Therefore, the conditional probability of a common cause failure was included in the analysis for those components that failed as part of the event. This was implemented in the model by setting the serial component failure probability equal to the conditional probability that the remaining pumps would fail, given failure of pump B (0.1 x 0.3). Since failure of either remaining pump would have rendered AFW inoperable for ATWS mitigation, the failure probability of AFW during ATWS was calculated as 0.1 + 0.1 = 0.2.
LER No. 281/83-055
B.13-2 B.13.5 Analysis Results The conditional core damage probability estimated for this event is 3.5 x 10-. The dominant sequence for this event, highlighted on the event tree in Figure B. 13.1, involves a transient with reactor trip success, failure of main and auxiliary feedwater, and failure of feed-and-bleed cooling.
LER No. 281/83-055
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Figure B.13.1 Dominant core damage sequence for LER 281/83-055 LER No. 281/83-055
B.13-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 281/83-055 Event
Description:
Trip with AFW pump inop Event Date: November 18. 1983 Plant: Surry 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OE+O0 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 3.5E-05 Total 3.5E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
121 trans -rt AFW mfw feed.bleed CD 2.7E-05 1.5E-01 508 trans rt -prim.press.limited AFW/ATWS CD 5.6E-06 1.0E-01 119 trans -rt AFW mfw -feed.bleed recov.sec.cool -csr hpr CD 8.8E-07 1.5E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
119 trans -rt AFW mfw -feed.bleed recov.sec.cool -csr hpr CD 8.8E-07 1.5E-01 121 trans -rt AFW mfw feed.bleed CD 2.7E-05 1.5E-01 508 trans rt -prim.press.limited AFW/ATWS CD 5.6E-06 1.OE-01
- non-recovery credit for edited case SEQUENCE MODEL: d:\asp\models\pwra8283.cmp BRANCH MODEL: d:\asp\models\surry2.82 PROBABILITY FILE: d:\asp\models\pwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 1.9E-03 1.OE+O0 loop 1.6E-05 5.3E-01 loca 2.4E-06 5.4E-01 LER No. 281/83-055
B.13-5 sgtr 1.6E-06 1.OE+00 rt 2.8E-04 1.0E-01 rt(loop) 0.0 E+00 1.OQE+00 AFW 3.8E-04 > 3.1E-02 4.5E-01 Branch Model: 1.OF.3+ser Event Identifier: 281/83-055 Train I Cond Prob: 2.OE-02 Train 2 Cond Prob: 1.OE-01 > 1.0E+00 Train 3 Cond Prob: 5.OE-02 Serial Component Prob: 2.8E-04 > 3.OE-02 AFW/ATWS 4.3E-03 > 2.OE-01 1.OE+00 Branch Model: I.OF.1 Train 1 Cond Prob: 4.3E-03 > 2.OE-01 afw/ep 5.OE-02 3.4E-01 mfw 1.9E-01 314E-01 1.OE-03 porv.chall 4.OE-02 1.OE+00 porv.chall/afw 1.OE+00 1.OE+00 porv.chall/loop 1.OE-01 1.OE+00 porv.chall/sbo 1.OE+00 1.0E+00 porv.reseat 2.OE-02 1.1E-02 porv.reseat/ep 2.OE-02 1.OE+00 srv.reseat(atws) 1.OE-01 1.OE+00 hpi 1.5E-03 8.9E-01 feed.bleed 2.OE-02 1.OE+00 1.OE-02 emrg.boration 0.OE+00 1.OE+00 1.OE-02 recov.sec.cool 2.OE-01 1.0E+00 recov.sec.cool/offsite.pwr 3.4E-01 L..E+00 rcs.cooldown 3.OE-03 1.OE+00 1.OE-03 rhr 2.2E-02 7.OE-02 1.OE-03 csr 7.5E-04 1.OE+00 hpr 4.OE-03 1.OE+00 1.OE-03 ep 2.9E-03 8.9E-01 seal.loca 2.7E-01 1.OE+00 offsite.pwr.rec/-ep.and.-afw 2.2E-01 1.OE+00 offsite.pwr.rec/-ep.and.afw 6.7E-02 1.OE+00 offsite.pwr.rec/seal.loca 5.7E-01 1.OE+00 offsite.pwr.rec/-seal.loca 7.0E-02 1.0OE+00 sg.iso.and.rcs.cooldown 1.OE-02 1.OE-01 rcs.cool.below.rhr 3.OE-03 1.OE+00 3.OE-03 prim.press.limited 8.8E-03 1.OE+00
- branch model file
- forced LER No. 281/83-055