ML20156A251
| ML20156A251 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1986-011-00 | |
| Download: ML20156A251 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.:
Event
Description:
Date of Event:
Plant:
389/86-011 Emergency power system is unavailable July 9, 1986 St. Lucie 2 EVENT DESCRIPTION Sequence At 0854 h the 2-A emergency DG was started for a surveillance test conducted once every 7
- d.
The 2-A DG failed to meet the required generator voltage and frequency within 10 s after the start signal.
One of the two engines in the 2-A DG set had failed to start.
The 2-A DG was manually tripped by the operator at 0856 h.
At 0915 h the redundant 2-B DG was started.
At 0917 h, 2-B DG was stopped because an operator observed 1 of the 12 cylinder cooling fan blades rubbing the cooling fan shroud.
The unit remained at 100% power throughout this event.
Corrective Action 2-B DG was repaired and returned to service at 1059 h.
Trouble-shooting of the 2-A DG revealed a problem in the mechanical portion of the Woodward governor.
The problem was corrected, and 2-A DG was returned to service at 2010 h.
Plant/Event Data Systems Involved:
Emergency power generation system Components and Failure Modes Involved:
2A DG -
failed in testing 2B DG -
failed in testing Component Unavailability Duration:
surveillance period)
Plant Operating Mode:
1 (100% power)
Discovery Method:
Surveillance test Reactor Age:
3.1 years Plant Type:
PWR 84 h assumed (half of the 7-d Event Identifier:
389/86-011 D-121
Comments LER 389/86-011 states that the fan rub associated with DG 2-B was minor.
If the fan rub was minor in the sense that even with the fan rub, the DG would have operated for its mission time, then the emergency power system unavailability should be based on the maintenance unavail-ability period (-1 3/4 hours).
- However, if the fan rub was minor in the sense that it was easily repaired, but with the rub the DG would not have operated for its mission time, then an emergency power system unavailability based on the surveillance period is warranted.
Since it is not possible to distinguish between these two cases based on informa-tion provided in the LER, a more conservative estimate based on surveil-lance internal was assumed.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Postulated LOOP Base case nonrecovery Branches Impacted and Branch Nonrecovery Estimate EPS 1.0 Given a
Plant Models Utilized PWR plant Class G Event Identifier:
389/86-011 D-122
CONDITIONAL CORE DAMASE PROBABILITY CALCULATIONS Event Identifier:
389186-011 Event
Description:
Eaerqency Power System Is Unavailable Event Date:
7/9/86 Plant:
St Lucie 2 UNAVAILABILITY, DURATION= 84 NON-RECOVERABLE INITIATINS EVENT PROBABILITIES LOOP SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator 1.5E-04 Probability CV LOOP Total 7.5E-07 7.5E-07 CD LOOP Total 2.6E-O6 2.6E-06 ATWS LOOP Total O.OE+00
- 0.
OE+OO DOMINANT SEQUENCES End State:
CV Conditional Probability:
7.4E-07 211 LOOP -RT/LOOP EMERG.PONER -AFW/EMERS.POWER -PORV.OR.SRV.CHALL SS.RELEAS.TERM End State:
CD Conditional Probability:
2.6E-06 212 LOOP -RT/LOOP EMER6.PONER AFW/EMERB.POWER SEQUENCE CONDITIONAL PROBABILITIES Event Identifier: 389/86-011 D-123
Sequence End State Prob N Rec**
211 LOOP -RT/LOOP EMERGPOWER -AFW/EMERB.POWER -PORV.OR.SRV.CHALL SS.RELEAS.TERN 212 LOOP -RTILOOP EMERG.POWER AFW/EMERS.POWER Cv CD 7.4E-07
- 1.3E-01 2.6E-06
- 1.3E-01
- dominant sequence for end state H non-recovery credit for edited case Note:
For unavailabilities, conditional probability values are differential values which reflect the added risk due to failures associated with an event.
Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.
SEQUENCE MODEL:
BRANCH MODEL:
PROBABILITY FILE:
ct\\asp\\newmodel\\pwrgtree.cep c:\\asp\\newmodel\\Iucie.txt c:\\asp\\newmodel\\pwr~b.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS LOOP LOCA RT RT/LOOP EMERB.POWER Branch Model:
1.OF.2 Train I Cond Prob:
Train 2 Cond Prob:
AFN AFW/ENERS.POWER MFW PORV.OR.SRV.CHALL PORY.OR.SRV.RESEAT PORV.OR.SRV.RESEAT/EMERS.POWER SS.RELEAS.TERN SB.RELEAS. TERM/-MFW SS.DEPRESS COND/MHF HPI HPI(F/B)
PORV.OPEN HPR/-HPI CSR
- branch model file Event Identifier: 389/86-011 4.BE-04 4.6E-06 2.4E-06
- 2. BE-04
- 0.
OE+00 2.9E-03 ) 1.OE+00
- 5. E-02 5.7E-02
- 3. BE-04 5.0E-02 1.9E-01
- 2. E-02 l.OE-02 1.0E-02 1.5E-02 1.SE-02 3.bE-02 1.OE+00 3.0E-04 3.OE-04 1.0E+00 1.5E-04
- 2. OE-03
> Unavailable
> Unavailable I
. OE +00 3.9E-01
- 4.
- 1.
2E-01 J.
OE+00 B.OE-01 1,I.E+00 2.,6E-01 3,4E-01 3.4E-01
- 1.
OE+00
- 5.
OE-02 1.OE+00 3.4E-01
- 3.
E-01 110E+00
- 3.
- 8.
4E-01 1
.0E+00 1.0E+00
- 3.
- 4.
OE-02 D-124
- forced Austin 09-11-1987 12:47 115 Event Identifier: 389/86-011 D-125