ML20149K403
| ML20149K403 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-019-00 | |
| Download: ML20149K403 (5) | |
Text
B.20-1 B.20 LER No. 309/83-002 Event
Description:
Transient with MFW Inoperable and One Isolated Steam Generator Date of Event: January 25, 1983 Plant: Maine Yankee B.20.1 Summary On January 25, 1983, Maine Yankee tripped from a full load while isolating an electrical ground. Main feedwater (MFW) was unavailable after the trip and auxiliary feedwater (AFW) auto-started and provided cooling to the steam generators. Approximately 15 minutes after the trip, indications were received that a main feedwater line break had occurred. The estimated conditional core damage probability for this event is 8.6 x 10-5.
B.20.2 Event Description On January 25, 1983, Maine Yankee tripped from full load while an electrical ground was being isolated.
Main feedwater was not available after the trip due to the trip of the turbine-driven pump and maintenance on both motor-driven pumps [NUREG-0090-Vol. 6-No.1 1]. Approximately 15 minutes later, a loud noise was heard in the plant machine shop, and a containment fire detector alarmed. Containment humidity also began to rise. The containment was entered for inspection and a feedline leak was discovered near the number 2 steam generator inlet nozzle. Station cooldown was initiated to permit close access for further inspection and repairs. Further investigation revealed that the leak likely occurred due to water hammer, which resulted in the failure of an existing crack in the feed pipe. The feedline leak was at most 100 gpm [NUREG-0090-Vol.6-No.11] and all AFW pumps were functional at the time of the incident.
B.20.3 Additional Event-Related Information The Maine Yankee MFW system consists of one turbine-driven pump and two motor-driven pumps. AFW system consists of two motor-driven pumps and one turbine-driven pump. Any one of the three AFW pumps can supply sufficient water to remove decay heat from the steam generators.
B.20.4 Modeling Assumptions This event was modeled as a transient with MFW failed. The MFW branch probability was set to failed, and the nonrecovery probability was set to 1.0 to reflect the likelihood that operators would not have been able to recover MFW within the allowable time during the transient.
LER No. 309/83-002
B.20-2 The -100 gpm leak rate experienced from the feedwater line to SG2 was relatively large compared to the output of a single AFW pump. Therefore, AFW success was assumed to require operation of two of three AFW pumps. The AFW branch failure probability was revised to reflect this.
B.20.5 Analysis Results The estimated conditional core damage probability for this event is 8.6 x 10'. The dominant sequence, highlighted on the event tree in Figure B.20. 1, involves a successful reactor trip, the failure of AFW, the failure of MFW, and the failure of feed and bleed.
LER No. 309/83-002
B.20-3 00C 88 ;8 V 2:88 r 0,
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Figure B.20.1 Dominant core damage sequence for LER 309/83-002 LER No. 309/83-002
B.20-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 309/83-002 Event
Description:
Transient with MFWinoperable and one SG isolated Event Date: January 25, 1983 Plant: Maine Yankee INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OE+O0 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 8.6E-05 Total 8.6E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
120 trans -rt afw MFW feed.bleed CD 8.2E-05 4.5E-01 119 trans -rt afw MFW-feed.bleed recov.sec.cool hpr CD 2.7E-06 4.5E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
119 trans -rt afw MFW-feed.bleed recov.sec.cool hpr CD 2.7E-06 4.5E-01 120 trans -rt afw MFW feed.bleed CD 8.2E-05 4.5E-01
- non-recovery credit for edited case SEQUENCE MODEL: c:\aspcode\models\myank82.cmp BRANCH MODEL: c:\aspcode\models\myankee.82 PROBABILITY FILE: c:\aspcode\models\pwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 6.5E-04 I.OE+O0 loop 2.0E-05 5.8E-01 loca 2.4E-06 5.4E-01 LER No. 309/83-002
B.20-5 sgtr 1.6E-06 1.OE+00 rt 2.8E -04 1.OE-01 rt(loop) 0.OE+00 1.OE+00 afw 6.1E-03*** 4.SE-01, afw/atws 4.3E-03 1.OE+00 afw/ep 5.OE-02 3.4E-01 MFW 1.9E-01 > 1.OE+00 3.4E-01 > 1.OE+00 Branch Model: 1.OF.1 Train 1 Cond Prob: 1.9E-01 > Failed porv.chall 4.OE-02 1.OE+00 porv.chall/afw 1.OE+00 1.OE+00 porv.chall/loop 1.OE-01 1.OE+00 porv.chall/sbo 1.OE+00 1.OE+00 porv.reseat 2.OE-02 1.1E-02 porv.reseat/ep 2.OE-02 1.OE+00 srv.reseat(atws) 1.OE-01 1.OE+00 hpi 3.OE-04 8.9E-01 feed.bleed 2.OE-02 1.OE+00 1.OE-02 emrg.boration Q.OE+00 1.0E+00 1.OE-02 recov.sec.cool 2.DE-01 1.OE+00 recov.sec.cool/offsite.pwr 3.4E-01 1.OE+00 rcs.cooldown 3.OE-03 1.OE+00 1.OE-03 rhr 3.1E-02 7.OE-02 1.OE-03 hpr 4.OE-03 1.OE+00 1.OE-03 ep 2.9E-03 8.9E-01 seal loca 5.5E-02 1.OE+00 offsite.pwr.rec/-ep.and.-afw 3.2E-01 1.OE+00 offsite.pwr.rec/-ep.and.afw 1.1E-01 1.OE+00 offsite.pwr.rec/seal.loca 6.5E-01 1.OE+00 offsite.pwr.rec/-seal.loca 2.3E-01 1.OE+00 sg.iso.and.rcs.cooldown 1.OE-02 1.OE-01 rcs.cool.below.rhr 3.OE-03 1.OE+00 3.OE-03 prim.press.limited 8.8E-03 1.OE+00
- branch model file
- forced
- branch probability reflects the requirement for 2 of 3 AFW pumps for success.
LER No. 309/83-002