ML20161A164
| ML20161A164 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1986-038-00 | |
| Download: ML20161A164 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 250/86-038 Event
Description:
System is unavailable AFW Date of Event: December 4, 1986 Plant: Turkey Points 3 and 4 EVENT DESCRIPTION Sequence During routine testing, AFW pump B of AFW train 2 unexpectedly tripped off on an overspeed trip (the set point had drifted). Because the station AFW consists of three turbine-driven pumps (pumps B and C on train 2 and pump A on train 1), pump C was placed in service. Personnel then discovered pump C's steam supply valve (MOV-3-1403) failed to open. Train A was available but could not service both Units 3 and 4.
After trains B and C were restored to service, unit 4 AFW motor valves were inspected. The alignment of the valves rendered one train inoperable.
Corrective Action The AFW pump B trip set point was adjusted. The valve MOV-3-1403 motor was replaced.
Plant/Event Data Systems Involved:
AFW Components and Failure Modes Involved:
Train B - failed in testing Train A - failed in testing Component Unavailability Duration: 360 h Plant Operating Mode: 1 (100% power)
Discovery Method: Testing Reactor Age: 14.2 (Unit 3) and 13.5 years (Unit 4), respectively Plant Type: PWR Comments Both units were affected by this event; however, this unavail-ability is a problem only if both MFW systems fail simultaneously, as in a station LOOP event. In a LOOP only one unit could be provided with sufficient AFW.
Event Identifier: 250/86-038 D-26
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Postulated LOOP Base case nonrecovery Branches Impacted and Branch Nonrecovery Estimate AFW 1.0 Recovery impossible without repair and local troubleshooting Plant Models Utilized PWR plant Class E Event Identifier: 250/86-038 D-27
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 250/86-038 Event
Description:
Unavailability of Auxiliary Feedwater Event Date: 12/4/86 Plant: Turkey Point 3 UNAVAILABILITY, DURATIONz 360 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 6. E-04 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV LOOP i 7.9E-09 )
Total ( 7.9E-09 )
CD LOOP 5. BE-05 Total 5. BE-05 ATWS LOOP 0.OE+00 Total 0.OE+00 DOMINANT SEQUENCES End State: CD Conditional Probability: 2.6E-05 214 LOOP -RT/LOOP -EMERB.POWER AFN HPI(F/B)
SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prob N Recet 212 LOOP -RT/LOOP -EMERG.POWER AFN -HPI(F/B) -HPR/-HPI PORV.OPEN CD 5.9E-06 *3.9E-01 213 LOOP -RT/LOOP -EMERG.POWER AFW -HPI(F/B) HPR/-HPI CD 2.5E-05 *3.9E-01 Event Identifier: 250/86-038 D-28
214 LOOP -RTI/LOOP -EMERB.POWER AFW HPI(FIB) CD 2.6E-05
- 3.3E-01 218 LOOP -RTI/LOOP EMERG.POWER AFW/EMERO.POWER CD 1.5E-0b 3.1E-01
- dominant sequence for end state
,e 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: c:\asp\newmodel\pwrbtree.cup BRANCH MODELi c:\asp\newmodel\turkey.txt PROBABILITY FILE: c:\asp\neBWodel\pwr~b.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch system Non-Recov Opr Fail TRANS 4.JE-04 I. OEWO LOOP 4.6E-06 3.9E-01 LOCA 2.4E-06 4.3E-01 RT 2. BE-04 1.2E-01 RT/LOOP 0.OE+00 1.0E+00 EMER.,POWER 2.9E-03 B.OE-01 AFW 1.5E-03 > 1.OE+00 2.7E-01 > I.OE+00 Branch Model: 1. OF,3 Train I Cond Prob: 5. OE-02 > Unavailable Train 2 Cond Prob: I.OE-01 > Unavailable Train 3 Cond Prob: 3.OE-0I > Unavailable AFW/EMERBPONER 1.5E-03 > I.OE+O0 2.7E-O1 ) I.OE+00 Branch Model: 1.OF,3 Train 1 Cond Prob: 5. OE-02 > Unavailable Train 2 Cond Prob: I.OE-OI > Unavailable Train 3 Cond Prob: 3.OE-01 > Unavailable MFW I.9E-01 3.4E-01 PORV.OR.SRV.CHALL 4.OE-02 I.OE+00 PORV.OR.SRV.RESEAT 2. OE-02 5.OE-02 PORV.ORSRV.RESEAT/EMERG.POWER 2.OE-02 1.0E+00 SS.RELEAS.TERM 1.5E-02 3.4E-01 5S.RELEAS. TERM/-MFW 1.5E-02 3.4E-01 HPI 3. DE-04 B.4E-01 HPI(F/B) 3.OE-04 B 4E-01 4.OE-02 HPR/-HPI 1.3E-04 1.OE+00 4. DE-02 PORV.OPEN I.OE-02 1.OE+00 8S.DEPRESS 3.6E-02 i.OE+00 COND/MFW 1.OE+00 3.4E-01 LpI/HPI i.SE-04 3.4E-01 Event Identifier: 250/86-038 D-29
LPR/-HPIHPR 6.7E-01 1.OE+00 LPR/HPl 1.5E-04 1.OE+O0
- branch sade! file cc forced Austin 09-11-1987 11t14:36 Event Identifiers 250/86-038 D-30