ML20149K494
| ML20149K494 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-022-01 | |
| Download: ML20149K494 (5) | |
Text
3-20 Accident Sequence Precursor Program Event Analysis LER No: 219/88-022 Ri Event
Description:
Trip with one safety-related bus unavailable Date of Event: October 2, 1988 Plant: Oyster Creek Unit 1 Summnary During a refueling outage, power to an emergency 4160-V bus was lost when a breaker tripped and locked out due to a ground fault on the bus. Because this event could have happened at power, it has been modeled as a trip with one safety-related bus unavailable. The condi-tional probability for core damage is calculated at 5.0 6. The relative significance of this event compared with other potential events at Oyster Creek Unit 1 is shown below.
Event Description During a refueling outage on Oct. 2, 1988, at 1357 h, power was lost to safety-related 4160-V Bus 1D when a breaker tripped and locked out due to a ground fault on a cable between Bus 1D and the diesel generator No. 2 breaker. The root cause of the cable failure was determined Lo be a defect in the cable insulation. The lockout of the faulted bus pre-vented the No. 2 emergency diesel generator from starting. The loss of power on the bus generated a reactor protection system actuation, which caused a full reactor scram signal and a main steam line isolation since RCS pressure was <600 psig. At 1506 h, power was restored to the reactor protection system No. 2 channel, allowing operators to reset the scram and main steam line isolation signals. At approximately 2130 h, the cable fault was isolated and power was restored to the 4160-V Bus 1D.
B-21 At 0140 h the next morning, operators were manually restoring normal power to instrument panel VACP-l when a momentary loss of power caused isolation of the drywell and torus vent and purge valves, drywell sump, the drywell equipment drain tank, and the realignment of the circuitry for the standby gas treatment system to autostart. All systems were returned to normal shortly after the normal power supply to VACP-l was restored.
Event-Related Plant Design Information Oyster Creek Unit 2 has two diesel generators that provide emergency power to vital 4160-V loads. Diesel No. 2 provides power to bus ID, which supplies a core spray pump, an emergency service water pump, con-tainment spray pump, and various other 4160-V vital loads and 480-V emergency busses.
ASP Modeling Assumptions and Approach The event has been modeled assuming that it could have occurred at power, and that if that were the case, a reactor scram would have also resulted.
Analysis Results The conditional probability of core damage estimated for the event is 5.0 x 10-6, which is indicative of a low significance event. The dominant core damage sequence involves failure of an SRV to close, fail-ure of FWCI,, and failure to depressurize to RPV, as shown on the fol-lowing event tree. An almost equally significant sequence involves successful depressurization, failure of core spray, and failure to utilize fire water in conjunction with shutdown cooling to mitigate the open SRV.
B-222 lENT S1HUT PO DON CHAL R- ~p F WIADS LPS SO OTHSTAR O TT OK OK OK II COREDAMAGE OK OK 12 COREDAMAGE OK 13 COýRE DAMAGE OX OK 14 COREDAMAGE OK i5 COREDAMAGE Lr OK 10 COREDAMAGE 17 COREDAMAGE 15 COREDAMAGE O0 OK
- 1. COR DAMAGE 20 COREDAMAGE OK OK 21 COREDAMAGE 2 COREDMG 22 COREDAMAGE OK OK 2K OK 21 COREDAMAGE OK OK 27 COREDAMAGE OK
.K 28 COREDAMAGE OK 29 COREDAMAGE OK 31 COREDAMAGE 3 COREDMG 3- COREDAMAGE SS ATWS Dominant Core Damage Sequence for LER 219/88-022 RI
B- 23 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 219/88-022 Event
Description:
Trip with one safety-related bus unavailable Event Date: 10/02/88 Plant: Oyster Creek INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1. OE+00 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD TRANS 5. OE-06 Total 5. OE-06 AIMS TRANS 3. OE-05 Total 3. OE-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
SequenceE nd State Prob N Rec**
25 trans -rx.shutdown pcs srv.chali/trans.-scram srv.close fw/p D0 2. 5E-06 2 .4E-Ol cs.trans fwci/fw.trans srv.ads 22 trans -rx.shutdown pcs srv.chall/trans.-scram srv.close fw/p C D0 2. OE-06 1.1lE-01 cs.trans fwci/fw.trans -srv.ads LPCS -SOC firewater 20 trans -rx.shutdown pcs srv.chall/trans.-scram srv.close fw/p D0 1. 6E-07 3. 2E-01 cs.trans -fwci/fw.trans SOC CC/SOC 12 trans -rx.shutdown pcs srv.chall/trans.-scram -srv.close isol C D0 1. 3E-07 3. 2E-01
.cond fw/pcs.trans -fwci/fw.trans SOC CC/SOC 99 trans rx.shutdownA TIWS 3.OE-05 1.0E+00
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence E:nd State Prob N Rec**
12 trans -rx.shu.tdown pos srv.chall/trans.-scram -srv.close isol C:0 1. 3E-07 3 .2E-01
.cond fw/pcs.trans -fwci/fw.trans SOC CC/SOC 20 trans -rx.shutdown pcs srv.chall/trans.-scram srv.close fw/p C D0 1. 6E-07 3 .2E-01 cs.trans -fwci/fw.trans SOC CC/SOC 22 trans -rx.shutdown pcs srv.chali/trans.-scrars srv.close fw/p C D0 2. GE-OS 1. 1E-01.
cs.trans fwci/fw.trans -srv.ads LPCS -SOC firewater 25 trans -rx.shutdown pcs srv.chall/trans.-scram srv.close Sw/p D0 2.SE-0 6 2 .4E-01 cs.trans fwci/fw.trans srv.ads 99 trans rx.shutdownA TIWS 3. OE-05 1 .OE+0O
-* non-recovery credit for edited case SEQUENCE MODEL: c:\asp\sealmod\bwraseal .cmp BRANCH MODEL: c:\asp\sealmod\oyster.sll PROBABILITY FILE: c:\asp\sealmod\bwr~csll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail Event Identifier: 219/88-022
B- 24 trans 2. 6E-04 1.0 0+00 loop 1. 6E-05 3. GE-01 loca 3.3E-0 6 5.0OE-01 rx. shutdown 3.0OE-05 1.00+00 rx. shutdown/ep 3.5E-04 1.00+00 PCs 1. 7E-01 1.00+00 srv.chall/trans.-scram 1.00E+00 1.00+00 srv.chall/loop .-scrars 1. OE+0O 1 .00+00 srv.close 1.2E-02 1 .00+00 eme r . power 2. 9E-03 6.00-01 ep. rec 1. 6E-01 1.00+00 fw/pcs .trans 1. 00+00 1.00+00 fwci/fw.trans 2. 9E-01 3.4E-01 fwci/loop 1.00+00 1.00+00 fwci/loca 1. OE-03 3.40-01 isol .cond 1. OE-02 1 .00+00 c rd 1. OE-02 1 .00+00 1 .OE-02 a rv. ads 3. 7E-03 7. 10-01 1.00E-02 LPCS 3.00-03 > 3.OE-02 3.4E-01 Branch Model: l.OF.2 Train 1 Cond Prob: 3.OE-03 > 3.00-02 Train 2 Cond Prob: 1. OE+00 SDC 2.1E-02 > 2.3E-02 3.40-01 1.00-03 Branch Model: 1.OF.3+ser+opr Train 1 Cond Prob: 3.0 0-02 Train 2 Cond Prob: 1.00-01 Train 3 Cond Prob: 3.00-01 > Unavailable Serial Component Prob: 2.00-02 CCISDC 1.OE-03 > 1.00-02 1.00+00 Branch Model: 1.OF.2 Train 1 Cond Prob: 1 .OE-02 Train 2 Cond Prob: 1.00-01 > Unavailable firewater 1.00+00 1. 0 +00 2 .00-03
- branch model file
- 'forced Minarick 11-14-1989 11:59:46 Event Identifier: 219/88-022