ML20149K487
| ML20149K487 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1986-001-00 | |
| Download: ML20149K487 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 269/86-001 Event
Description:
Trip, LOFW, and a stuck-open MSRV occur Date of Event: January 31, 1986 Plant: Oconee 1 EVENT DESCRIPTION Sequence At 1546 h during troubleshooting, circuit breaker PCB-24 was man-ually closed without the reset of the generator lockout relays. When the breaker was closed, the relay logic was satisfied, causing a yellow bus lockout. Consequently, all the 230-kV yellow-bus tie breakers opened.
One of the breakers that opened was PCB-21, the generator to the yellow-bus tie breaker. When it opened, the only path for current flow from the generator to the switchyard was via PCB-20. PCB-20 faulted, undergoing an explosion, -17 seconds after PCB-21 opened. At 1547 h the turbine/generator tripped, initiating an anticipatory reactor trip from 100% stable power conditions.
Following the reactor trip, both MFWPs tripped on high discharge pressure. A preliminary investigation showed that the MFWP speed demand did not run back as expected. All three EFW pumps started immediately to supply feedwater flow for DHR.
Following the reactor trip, one of the MSRVs (IMS-8) opened and stuck open for 11 min. It reseated when the SG pressure decreased to 975 psig, the minimum RCS pressure was 1750 psig.
Unit 1 was stabilized at hot shutdown conditions with no actuations of engineering safeguard systems or pressurizer relief valves, and no RCS leakage was induced.
Corrective Action PCB-20 was repaired. The MFWP trip set points were reviewed. The MSRV (IMS-8) was repaired.
Plant/Event Data Systems Involved:
MFW, main steam relief, electrical Event Identifier: 269/86-001 D-42
Components and Failure Modes Involved:
MSRV - stuck open in operation MFWPS - tripped off in operation Component Unavailability Duration: NA Plant Operating Mode: 1 (100% power)
Discovery Method: Operational event Reactor Age: 12.8 years Plant Type: PWR Comments None MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 No recovery Branches Impacted and Branch Nonrecovery Estimate MFW 1.0 No recovery possible in the short term SS release 0.12 MSRV stuck open but closed on lower terminated pressure Plant Models Utilized PWR plant Class D Event Identifier: 269/86-001 D-43
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 269/B6-001 Event
Description:
Trip, LOFW, and Stuck Open MSRV Event Date: 1/31/O6 Plant: Oconee I INITIATING EVENT NON-RECOVERABLE INITIATIN6 EVENT PROBABILITIES TRANS i.OE+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 3.2E-05 Total 3.2E-05 CD TRANS 2.1 E-06 Total 2. 1E-06 ATWS TRANS 3.4E-05 Total 3.4E-05 DOMINANT SEQUENCES End State: CY Conditional Probability: 2. BE-05 109 TRANS -RT -AFN -PORVOR.SRV.CHALL SS.RELEAS.TERM HP!
End State: CO Conditional Probability: I.OE-06 103 TRANS -RT -AFN PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HPR/-HPI -5S.DEPRESS LPR/-HP I.HPR End State: ATWS Conditional Probability: 3.4E-05 Event Identifier: 269/86-001 D-44
126 TRANS RT SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prob NRec*#
101 TRANS -RT -AFWPORV.OR.SRV,CHALL -PORV.OR.SRV.RESEAT SS,RELE CV 2.4E-06 1.OE-01 AS.TERM HP!
103 TRANS -RT -AFW PORVORBRVCHALL PORV.OR.SRV.RESEAT -HPI HP CD 1.OE-06
- 5.OE-02 R/-HPI -SS.DEPRESS LPRI-HPI.HPR 104 TRANS -RT -AFW PORV.OR.SRVCHALL PORV.OR.SRV.RESEAT -HPI HP CD 5.8E-08 5.OE-02 R/-HPI SS.DEPRESS 109 TRANS -RT -AFN -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI CV 2.8BE-05 4 1.OE-01 123 TRANS -RT AFN MFW -HPI(F/B) HPR/-HPI -5S.DEPRESS COND/MFW CD 4.2E-07 3.OE-02 124 TRANS -RT AFN MFW -HPI(F/B) HPR/-HPI SS.DEPRESS CD 4.7E-08 8.BE-02 125 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESB -COND/MFW CV 8.6E-07 4.9E-02 126 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS COND/MFW CD 4.4E-07 2.5E-02 127 TRANS -RT AFW MFW HPI(F/B) SB,DEPRESS CD 4.9E-08 7.4E-02 128 TRANS RI ATWS 3.4E-05 1.2E-01
- dominant sequence for end state
- 4 non-recovery credit for edited case SEQUENCE MODEL: c:\asp\newmodel\pwrdtree.cap BRANCH MODEL: c:\asp\newmodel\oconee.txt PROBABILITY FILE: c:\asp\newmodel\pwrb.pro No Recovery Limit BRANCH FREgUENCIES/PROBABILITIES Branch System Non-Recoy Opr Fail TRANS 4,SE-04 1.OE+00 LOOP 4.6E-06 3.9E-01 LOCA 2.4E-06 4.3E-01 RT 2.8E-04 1.2E-01 RT/LOOP OOE+00 1.OE+00 EMER6.POWER 2.9E-03 8.OE-01 AFW 3.BE-04 2.6E-O1 AFW/EMERS..POWER 5.OE-02 3.4E-01 MFW 2.OE-01 > 1.OE+00 3.4E-01 Branch Model: 1.OF.1 Train I Cond Prob: 2.OE-01 > Failed PORV.OR.SRV.CHALL - B.OE-02 1.OE+00 PORV.OR.SRV,RESEAT 1.OE-02 5. OE-02 PORV.OR.SRV.RESEAT/EMERG.POWER I.OE-02 1.0E+00 SS.RELEAS.TERM 1.5E-02 > L.OE+O0 3.4E-01 > 1.2E-01 Event Identifier: 269/86-001 D-45
Branch Modeli 1.DF.1 Train I Cond Prob: 1,5E-02 > Failed SS.RELEAS.TERM/-MFW 1.5E-02 > 1,OE+00 3.4E-01 > 1.2E-01 Branch Model: l.OF.,
Train I Cond Probi 1.5E-02 ) Failed HP! 3.OE-04 8.4E-01 HP1(F/B) 3. E-04 8.4E-01 4.0E-02 HPR/-HP! 1.5E-04 1.OE+00 4.OE-02 SS.DEPRESS 3.6E-02 1.QE +00 COMD/MFW I.OE+O0 3.4E-Oi LPI/HPI 1.5E-04 3.4E-01 LPR/-HPI.HPR b.7E-01 1.OE+00 LPR/HPI 1.5E-04 1,OE+00
- branch model file
- '.forced Austin 09-11-1987 11:25159 Event Identifier: 269/86-001 D-46