ML20161A157
| ML20161A157 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-028-00 | |
| Download: ML20161A157 (5) | |
Text
B-222 Accident Sequence Precursor Program Event Analysis LER No: 344/88-028 Event
Description:
Trip with one safety injection pump out for mainte-nance Date of Event: September 16, 1988 Plant: Trojan Summuary A trip from 100% power occurred while one train of the safety-injection system was out of service for maintenance. The conditional core damage probability estimated for this event is 1.9 x 10-6. The relative sig-nificance of this event compared with other potential events at Trojan is shown below:
-LER 344/88-028 1E-8 I1E-7 1E-6 IE-5 IE-4 I1E-3 1E-2 I
Trip - L EP Unavail Trip w/1 AFW (360 hrs)
Train Unavail LOOP AFW Unavail (360 hrs)
Event Description While establishing conditions necessary for replacement of a failed pressurizer pressure transmitter, a technician erroneously tripped the input bistable from another pressurizer pressure transmitter. This satisfied the two out of four overtemperature delta temperature (OTDT) trip logic, causing a reactor trip from 100% power. The trip occurred at approximately 0830. At that time, safety injection pump "B" was out of service for maintenance. Trains "A" and "B" of auxiliary feedwater (AFW) started. At 0905, it was discovered that the AFW control valve (CV-3004A1) for the "A" steam generator could not be throttled from the control room, due to a motor operator clutch lever being depressed by the motor power conduit. The conduit was improperly routed over the valve operator. The valve was properly positioned to deliver the correct AFW flow rate, however, and the cable was subsequently moved off the lever.
.1-223 ASP Modeling Assumptions and Approach This event was modeled with one train of safety injection unavailable following a trip. Because all trains of the AFW system were providing the required flow, the control valve that could not be throttled was not considered to be faulted.
Analysis Results The conditional probability of severe core damage estimated for this event is 1.9 x 10-6. The dominant sequence for core damage involves a failure of auxiliary feedwater (p = 8.5 x 10-4) and main feedwater (p = 0.07) following trip, and failure of feed and bleed (p = 0.018, including failure to initiate). This sequence is highlighted on the following event tree.
B-224 ZE FT TAS I
TRPW AW MW PORV/
9RV CHAL PORV/
SRV REETOE HPI HPR PORV OPN SEQ O
O END STATE OK OK CD 12 CD OK OK OK
- 13 CD 14 CD OK OK 156 CD 16 CD 17 CD 18 ATWS Dominant Core Damage Sequence for [ER 344/88-D28
3-225 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 344/88-028 Event
Description:
Trip with one Safety Injection pump unavailable Event Date: 09/16/88 Plant: Trtojan INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1. 0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 1. 9E-06 Total 1. 9E-06 ATWS TRANS 3. 4E-05 Total 3. 4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
17 trans -rt afw mfw HPI(F/B) CD 1. 1E-06 2. OE-02 15 trans -rt afw mfw -HPI(F/B) -hpr/-hpi porv.open CD 6. 1E-07 2. 4E-02 12 trans -rt -afw porv.or.srv.chall porv.or.srv.reseat ((PI CD 7. 4E-08 9. 2E-03 16 trans -rt afw mfw -HPI(F/B) hpr/-hpi CD 6. BE-08 2 .4E-02 i8 trans rt AIMS 3.4E-05 1.2E-01
-- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
12 trans -rt -afw porv.or.srv.chall porv.or.srv.reseat HPI CO 7. 4E-08 8. 21-03 15 trans -rt afw rnfw -RPI(F/B( -hpr/-hpi porv.open CD 6.1lE-07 2 .4E-02 16 trans -rt afw mfw -HPI(F/B( hpr/-hpi CD 6. 81-08 2 .4E-02 17 trans -tt afw mfw HPI(F/B) CD 1. 1E-06 2 .OE-02 is trans tt ATWS 3. 4E-05 1.2E-01
-non-recovery credit for edited case SEQUENCE NODEL: a: \seaimod\pwrbseal .cmp BRANCH MODEL: a:\sealmod\trojan.sll PROBABILITY FILE: a:\sealmod\pwr bsll .pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opt Fail trans 5. 6E-04 I1. OE+/-00 loop 1. 6E-05 3. 6E-01 inca 2 . 4E-068 4.3E-01 rt 2 .BE-04 1.2E-01 rt/ loop 0S.OE+/-IS 1. SE+SS eme rg. power 2 .9E-03 8.01-01 afw 2 .5E-03 3.4 E-01 Event Identifier: 344/88-028
9- 226 afw/emerg .power 2 .5E-03 3. 4E-01 mfw 1.00+00 7 .0E-02 porv.or.srv.chall 4.00E-02 1.00+/-00 porv.or.srv. resent 2 .0E-02 1. 10-02 porv.or.srv.rescat/emerg.power 2. 00-02 2. 0E+-00 seal. loca 2.3E-01 1.00+00 ep. rec si) 5. 9E-01 1.00+00 ep. rec 6. 1E-02 1 .00+00 HPI 1.00-03 > 1.OE-02 8.40-01 Branch M~odel: l.OF.2 Train 1 Coed Prob: 1 .00-02 Train 2 Cond Prob: 1.0Z-01 > Failed 522 (FIB) 1.OE-03 > 1.OE-02 8.40-01 1.00-02 Branch M4odel: 1.OF.2+opr Train 1 Cond Prob: 1.0 E-02 Train 2 Coed Prob: 1.00-01 > Failed hprl-hpi 1.5E-04 1. 00+/-00 1. OE-03 porv . pen 1 .0E-02 1.00+00 4.00-04 branch model file
- forced Minarick 11-12-1989 21:56:28 Event Identifier: 344/88-028