ML20156A218
| ML20156A218 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1983-063-00 | |
| Download: ML20156A218 (5) | |
Text
B.39-1 B.39 LER No. 361/83-063 Event
Description:
Trip with Motor-Driven AFW Pump Inoperable Date of Event: June 21, 1983 Plant: San Onofre 2 B.39.1 Summary A few days after a trip on Unit 2, an endurance test was performed on one of the Unit 3 motor-driven auxiliary feedwater (AFW) pumps (3P-504). During the test, the outboard bearing on the motor failed, and the pump was declared inoperable. Upon examination, it was discovered that the oil grooves in the AFW pump bearings were inadequate. Presumably, the bearings were not being lubricated properly. Similar bearing defects were discovered in the other Unit 3 motor-driven AFW pump (3P-141), and one of the two motor-driven AFW pumps on Unit 2 (2P-504). A trip had occurred on Unit 2 a few days earlier, while the AFW pump was presumably inoperable. The conditional core damage probability estimated for the event at Unit 2 is 1.1 x 10'.
B.39.2 Event Description While Unit 2 was shut down and Unit 3 was still precritical, a 48-hour endurance test was performed on the Unit 3 motor-driven AFW pump, 3P-504. During the run, the outboard bearing on the motor failed, rendering the pump inoperable. It was discovered later that the bearing oil grooves had been machined incorrectly and the bearing was apparently not being properly lubricated as a result. Similar problems were then identified with the other Unit 3 motor-driven AFW pump, 3P-141, and with the 2P-141 motor-driven AFW pump on Unit 2.
Low condenser vacuum caused a trip on Unit 2 on June 16, 1983.
B.39.3 Additional Event-Related Information A supplemental report to the licensee event report for this event indicated that the bearing machining error would not by itself cause bearing failure. However the report did indicate that the machining error, in conjunction with other normally acceptable conditions, could cause bearing failure. The other conditions which might be required were not specified.
B.39.4 Modeling Assumptions Since normally occurring conditions in conjunction with the bearing machining error could cause pump failure, it was assumed in this analysis that AFW pump 2P- 504 was inoperable in the long term. [The ASP models, like most PRA models, assume long-term (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) operability for AFW success.] As the bearing condition apparently existed since the pump's manufacture, it was assumed that the AFW pump was inoperable at the LER No. 361/83-063
B.39-2 time of the Unit 2 trip which occurred 5 days earlier. This event was modeled as an inoperability of train I of AFW in conjunction with the unit trip.
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.
The Unit 3 failures were not modeled, as Unit 3 was still in precritical status at the time.
B.39.5 Analysis Results The conditional core damage probability estimated for this event is 1.1 x 10'. The dominant core damage sequence, shown in Figure B.39. 1, involves reactor trip, failure of main and auxiliary feedwater, and failure to supply makeup from the condensate system.
LER No. 361/83-063
B.39-3 CO 000 0
0.z Ui 03:
Co.
a.
080 z
M a nw z
Figure B.39.1 Dominant core damage sequence for LER 361/83-063 LER No. 361/83-063
B.39-4 I
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 361/83-063 Event
Description:
Trip with AFW pump inoperable Event Date: June 21. 1983 Plant: San Onofre 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 1.1E-05 Total 1.1E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
119 trans -rt AFW mfw -srv.reseat cond CD 5.5E-06 1,SE-OI 508 trans rt -prim.press.limited AFW/ATWS CD 4.2E-06 I.OE-OI 118 trans -rt AFW mfw -srv.reseat -cond rcs.cooldown CD 3.1E-07 1.5E-OI 509 trans rt prim.press~limited CD 2.5E-07 1.OE-01 507 trans rt -prim.press.limited -AFW/ATWS emrg.boration CD 2.4E-07 I.OE-01 107 trans -rt -AFW srv.chall srv.reseat hpi CD 2.1E-07 8.9E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
107 trans -rt -AFW srv.chall srv.reseat hpi CD 2.1E-07 8.9E-01 118 trans -rt AFW mfw -srv.reseat -cond rcs.cooldown CD 3.1E-07 1.5E-01 119 trans -rt AFW mfw -srv.reseat cond CD 5.5E-06 1.5E-OI 507 trans rt -prim.press.limited -AFW/ATWS emrg.boration CD 2.4E-07 1.0E-01 508 trans rt -prim.press.limited AFW/ATWS CD 4.2E-06 I.OE-O1 509 trans rt prim.press.limited CD 2.5E-07 1,0E-OI
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\1982-83\pwrh8283.cmp BRANCH MODEL: c:\asp\1982-83\sanono2.82 PROBABILITY FILE: c:\asp\1982-83\pwr8283.pro No Recovery Limit LER No. 361/83-063
B.39-5 BRANCH FREQUENCIES/PROBABILITIES Branch System Non- Recov Opr Fail trans 1.17E-03 1.OE+00 1oop 2.OE-05 5.8E-01 1oca 2.4E -06 5.4E-01 sgtr 1.6E-06 1.OE+00 rt 2.8E -04 1.DE-01 rt(loop) 0.0 E+OQ 1.OE+00 AFW 3.8E-04 > 5.3E-03 4.5E-01 Branch Model: 1.OF.3+ser Train 1 Cond Prob: 2.0E-02 > Failed Train 2 Cond Prob: 1.CE-01 Train 3 Cond Prob: 5.OE-02 Serial Component Prob: 2.8E-04 AFW/ATWS 4.3E-03 > 1.5E-01 1.OE+00 Branch Model: 1.OF.1 Train I Cond Prob: 4.3E-03 > 1.5E-01 afw/ep 5.OE-02 3.4E-01 mfw 2.OE-01 3.4E-01 cond 2.5E-02 1.OE+00 1.OE-02 srv.chall 4.0 E-02 1.OE+00 srv.chall/afw 1.OE+00 1.0E+00 srv.chall/loop 1.QE-01 1.OE+00 srv .chal 1/sbo 1.OE+00 1.OE+00 srv. reseat 2.OE-02 1.OE+00 srv. reseat(atws) 1.0E-01. 1.0E+00 hpi 3.OE-04 8.9E-01 rhr 7.1E-03 5.7E-02 1.OE-03 hpr 2.OE-03 1.0E+00 ep 2.9E-03 8.9E-01 seal .loca 5.5E-02 1.OE+00 offsite.pwr.rec/seal loca 7.6E-01 1.OE+00 offsite.pwr.rec/-seal .loca 3.4E-01 1.OE+00 sg.iso.and. rcs.cooldown 1.OE-02 iQOE-01 1.OE-03 rcs.cooldown 1.OE-03 1.OE+00 rcs.cool.below.rhr 3.OE-03 1.0E+00 3.OE- 03 prim. press. limited 8.8E-03 1.OE+00 emrg.boration 0.OE+00 1.OE+00 1.OE-02
- branch model file
- forced LER No. 361/83-063