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 0.z 000 0
Ui a.
Co.
z0 3:
080 M
a z
nw Figure B.39.1 Dominant core damage sequence for LER 361/83-063 CO LER No. 361/83-063
B.39-4 I
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
Event
Description:
Event Date:
Plant:
361/83-063 Trip with AFW pump inoperable June 21. 1983 San Onofre 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS 1.0E+00 End State/Initiator Probability CD TRANS Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
- 1.
1E-05 1.1E-05 119 508 118 509 507 107 Sequence trans -rt AFW mfw -srv.reseat cond trans rt -prim.press.limited AFW/ATWS trans -rt AFW mfw -srv.reseat -cond rcs.cooldown trans rt prim.press~limited trans rt -prim.press.limited -AFW/ATWS emrg.boration trans -rt -AFW srv.chall srv.reseat hpi End State Prob CD CD CD CD CD CD 5.5E-06 4.2E-06 3.1E-07 2.5E-07 2.4E-07 2.1E-07 N Rec**
1,SE-OI I.OE-OI 1.5E-OI 1.OE-01 I.OE-01 8.9E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob 107 trans -rt -AFW srv.chall srv.reseat hpi 118 trans -rt AFW mfw -srv.reseat -cond rcs.cooldown 119 trans -rt AFW mfw -srv.reseat cond 507 trans rt -prim.press.limited -AFW/ATWS emrg.boration 508 trans rt -prim.press.limited AFW/ATWS 509 trans rt prim.press.limited
- non-recovery credit for edited case CD CD CD CD CD CD 2.1E-07 3.1E-07 5.5E-06 2.4E-07 4.2E-06 2.5E-07 N Rec**
8.9E-01 1.5E-01 1.5E-OI 1.0E-01 I.OE-O1 1,0E-OI SEQUENCE MODEL:
BRANCH MODEL:
PROBABILITY FILE:
No Recovery Limit c:\\asp\\1982-83\\pwrh8283.cmp c:\\asp\\1982-83\\sanono2.82 c:\\asp\\1982-83\\pwr8283.pro LER No. 361/83-063
B.39-5 BRANCH FREQUENCIES/PROBABILITIES Branch System trans 1 oop 1 oca sgtr rt rt(loop)
AFW Branch Model:
1.OF.3+ser Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Serial Component Prob:
AFW/ATWS Branch Model:
1.OF.1 Train I Cond Prob:
afw/ep mfw cond srv.chall srv.chall/afw srv.chall/loop srv.chal 1/sbo srv. reseat srv. reseat(atws) hpi rhr hpr ep seal.loca offsite.pwr.rec/seal loca offsite.pwr.rec/-seal.loca sg.iso.and. rcs.cooldown rcs.cooldown rcs.cool.below.rhr prim. press. limited emrg.boration 1.17E-03
- 2.
OE-05 2.4E -06 1.6E-06 2.8E -04 0.0 E+OQ 3.8E-04 > 5.3E-03 2.0E-02 > Failed 1.CE-01 5.OE-02 2.8E-04 4.3E-03 > 1.5E-01 4.3E-03 > 1.5E-01 5.OE-02 2.OE-01 2.5E-02 4.0 E-02 1.OE+00 1.QE-01 1.OE+00 2.OE-02 1.0E-01.
3.OE-04 7.1E-03 2.OE-03 2.9E-03 5.5E-02 7.6E-01 3.4E-01 1.OE-02 1.OE-03 3.OE-03 8.8E-03 0.OE+00 Non-Recov 1.OE+00 5.8E-01 5.4E-01 1.OE+00 1.DE-01 1.OE+00 4.5E-01 1.OE+00 3.4E-01 3.4E-01 1.OE+00 1.OE+00 1.0E+00 1.OE+00 1.OE+00 1.OE+00 1.0E+00 8.9E-01 5.7E-02 1.0E+00 8.9E-01 1.OE+00 1.OE+00 1.OE+00 iQOE-01 1.OE+00 1.0E+00 1.OE+00 1.OE+00 Opr Fail 1.OE-02 1.OE-03 1.OE-03
- 3.
OE- 03 1.OE-02 branch model file
- forced LER No. 361/83-063