ML20156A139
| ML20156A139 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1987-014-01 | |
| Download: ML20156A139 (4) | |
Text
B-48 PRECURSOR DESCRIPTION SHEET LER No.: 293/87-014 RI Event
Description:
LOOP and one DC removed from service for inspection Date of Event: 11/12/87 Plant: Pilgrim 1 EVENT DESCRIPTION Sequence During a severe winter storm, the startup transformer was feeding the plant electrical distribution systems through the normal outage con-figuration except that bus B2 was tied to Bus B4. The A and B D~s were in standby. The shutdown transformer was unavailable due to modifica-tion work in progress on the new blackout DG tie-in. The unit auxiliary transformer was ready for partial operation; several post-maintenance tests needed to be completed. The RHRS A pump was in shutdown cooling mode; the C pump was secured. The RHRS B and D pumps were in standby.
The A core spray train was in standby also; the B train was in mainten-ance. Two of five air compressors were also in maintenance. Of the remaining three compressors, one was operable but shut down. Backwash-ing of the main condenser was in progress.
At 0205 h offsite line 342 developed a phase A to phase C ground fault that tripped open two switchyard air circuit breakers (ACBs 103 &
104). ACB 104 opened too slowly and actuated the stuck breaker logic, which caused ACB 105 to trip. When ACB 105 tripped, it initiated a transfer sequence that tripped ACBs at the opposite end of line 342.
ACB 102 was still supplying power to the startup transformer via line 355. Then line 355 developed a phase B to C fault, which tripped its ACBs. Line 355 was reenergized in 0.5 s from the Bridgewater Station, but the ACB had already tripped. All ACBs in the switchyard were now open (0206 h), and a LOOP condition existed. Both DGs autostarted and supplied the vital buses. PCIS and scram occurred. Between 02 06 and 0215 h line 355 experienced multiple faults due to the high winds. The dispatcher ordered the Bridgewater breaker to be opened to prevent cycling and thereby preventing a short-term recovery of offsite power.
RHR A was briefly isolated when four fuses blew out, but SDC was restarted using pumps A and C. CRD pump A was shut down to prevent seal damage..
At 1135 h DG B was removed from service to investigate an ammeter problem. A prelube pump failure had also occurred. The restoration of offsite power was in progress but had not yet been accomplished. With DG B off, bus A-6 deenergized, disabling the air compressor supplying instrument air. Valves A0220-46 and -47 shut; they were providing a vent path from the vessel. A manual vent valve was opened. Thirty minutes later a second vent valve was opened. Power was restored to lines 342 and 355 at 1 415 h.
Event Identifier: 293/87-014 Ri
B-49 Corrective Action Repairs were made and a backup air supply will be installed.
Plant/Event Data Systems Involved:
Electrical Emergency power Components and Failure Modes Involved:
Offsite power lines fail on storm A DC is out for maintenance Component Unavailability Duration: 14 h Plant Operating Mode: 6 (0%)
Discovery Method: Operational event Reactor Age: 15.4 y Plant Type: BWR Comments For analysis purposes it has been assumed that the LOOP could have occurred at power. Removal of DC B for inspection has not been addressed in the at-power postulated event.
MODELINC CONSIDERATION AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP 1.0 No short-term recovery assumed possible Branches Impacted and Branch Nonrecovery Estimate None.
Plant Models Utilized BWR plant Class C Event Identifier: 293/87-014 Rl
B-50, CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 293/87-014RI Event
Description:
LOOP and one DG removed from service for inspection Event Date: 11/12/87 Plant: Pilgrim 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 1.OE+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 3.9E-04 Total 3. 9E-04 CV LOOP 1. 6E-05 Total 1.6E-D5 ATWS LOOP '7. E-0 6 Total 7_7E-D6 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
274 LOOP emerg.power -scram ep.rec CD 3.9E-04 1.4E-01 201 LOOP -emerg.power -scram srv.chall/loop.-scram -srv.close -hpci CV 1.3E-05 2.9E-01 rhr(sdc) rhr(spcool)/-lpci.rhr(sdc) -c.i.and.v -rhrsw(c.i.and.v 202 LOOP -emerg.power -scram srv.chall/loop.-scram -srv.close -hpci CV 2.6E-06 1.1E-01 rhr(sdc) rhr(spcool)/-lpci.rhr(sdc) -c.i.and.v rhrsw(c.i.and.v 846 LOOP -emerg.power scram slc.or.rods ATWS 6.9E-06 1.0E+00 841 LOOP emerg.power scram ATWS 8.OE-07 8.0E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec*-
201 LOOP -emerg.power -scram srv.chall/loop.-scram -srv.close -hpci CV 1.3E-05 2.9E-01 rhr(sdc) rhr(spcool)/-lpci.rhr(sdc) -c.i.and.v -rhrsw(c.i.and.v 202 LOOP -emerg.power -scram srv.chall/loop.-scram -srv.close -hpci CV 2.6E-06 1.1E-01 rhr(sdc) rhr(spcool)/-lpci.rhr(sdc) -c.i.and.v rhrsw(c.i.and.v 846 LOOP -emerg.power scram slc.or.rods ATWS 6.9E-06 1.0E+00 274 LOOP emerg.power -scram ep.rec CD 3.9E-04 1.4E-01 841 LOOP emerg.power scram ATWS 8.0E-07 8.OE-01
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\newmodel\bwrcnew.cmp BRANCH MODEL: c:\asp\newmodel\pilgrim.new Event Identifier: 293/87-014RI
B-51 PROBABILITY FILE: c:\asp\newmodel\bwr-cnew.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans S.6E-04 1.oOE00 LOOP 1.7E-05 > 1.7E-05 3.2E-01 > 1.OE+00 Branch Modell INITOR Initiator Freq: 1.7E-05 loca 3,3E-06 5.GE-01 scram 3.5E-04 1.OE+00 slc.or.rods l.OE-02 1.0E+00 1.OE-02 pcs/trans 1.7E-01 1.0E+00 srv.chall/trans.-scram 1.OE+00 1.0E+00 srv.chall/loop.-scram 1.0E+O0 1.0E+00 srv.close 1.3E-02 1.0E+00 emerg.power 2.9E,03 8.0E-01 ep.rec 1.0E+00 1.7E-01 fw/pcs.trans 2.9E-01 3.4E-01 fw/pcs.loca 4.0E-02 3.4E-01 hpci 2.9E-02 7.0E-01 rcic 6.0E-02 7.0E-01 crd I.OE-02 1.0E+00 1.0E-02 arv.ads 3.7E-03 7.1E-01 1.0E-02 cond/fw.pcs I.OE+00 3.4E-01 1.OE-03 lpcs 3.OE-03 3.4E-01 Ipci(rhr}/Ipcs I.0E-03 7.1E-01 rhr(adc) 2.1E-02 3.4E-01 1.0E-03 rhr(sdc)/-lpci 200E-02 3.4E-01 1.OE-03 rhr(sdc)/lpci 1.0E+00 1.0E+O0 1.0E-03 rhr(spcool)/-lpci.rhr(sdc) 2.0E-03 1.0E+00 rhr(spcool)/lpci.rhr(sdc) 5.2E-01 1.0E+00 c.i.and.v 1.0E-03 1.0E+00 101E-02 rhrsw 2.0E-02 3.4E-01 2.0E-03 rhrsw(c.i.and.v) 5.0E-01 3.4E-01
- branch model file
- forced Minarick 05-16-1989 06:59:22 Event Identifier; 293/87-014R1