ML20156A249
| ML20156A249 | |
| 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 1984-004-00 | |
| Download: ML20156A249 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 389/84-004 Event
Description:
LOFW, Failure of One AFW Train, and One MSRV Sticks Open Date of Event: February 9, 1984 Plant: St. Lucie 2 EVENT DESCRIPTION Sequence While the reactor was at 100% power, the MFWPs tripped due to low suction pressure. The reactor subsequently tripped on low SG level.
Following the trip, the 2C AFW pump started and then tripped on over-speed. A main steam SRV on the "A" SG also stuck partially open follow-ing the trip. Approximately 40 min was required to reseat the safe ty valve. Cooldown from the open safety valve was successfully controlled.
Corrective Action The cause of the low suction pressure to the MFWPs was not pbsi-tively determined. Condensate pump vent-line design probably con-tributed. The design is being changed to allow proper venting during strainer cleaning.
The 2C AFW pump tripped because of transients on a power supply during AEW actuation. The cause was not immediately known. However, repeated testing over a period of 6 d revealed the problem. A modifica-tion has been completed to eliminate this problem.
The SRV stuck open because a cotter pin was missing from a spindle nut. When the safety valve opened (as expected), the nut vibrated down and held the valve partially open. The nut pin was replaced, and all safeties were checked.
Plant/Event Data Systems Involved:
AFW and SG steam relief Components and Failure Modes Involved:
AFW pump - failed on demand MSRV -failed open in operation MFW -tripped during operation Event Identifier: 389/84-004 D-2 40
Component Unavailability Duration: NA Plant Operating Mode: 1 (100% power)
Discovery Method: Operational event Reactor Age: 0.7 year Plant Type: PWR Comments None MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate MFW 0.34 Recovery assumed locally at equipme~nt AFW Base case Degraded;'ý one train failed Secondary-side 1.0 No recovery assumed release terminated Secondary-side 1.0 No recovery assumed release terminated given MEW success Plant Models Utilized PWR plant Class G Event Identifier: 389/84-004 D-24 1
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 389/84-004 Event Description; LOFW With Failure of One AFW Train and Stuck-open MSRY Event Date: 2/9/84 Plant: St Lucie 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 5.OE-04 Total 5.OE-04 CD TRANS 2.OE-04 Total 2.OE-04 ATWS TRANS 3.OE-05 Total 3.OE-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 3.3E-04 112 TRANS -RT AFW MFW -HPI (F/B) -HPR/-HPI PORY .OPEN -96 .DEPRESS -COND/MFW End State: CD Conditional Probability: 1.7E-04 113 TRANS -RT AFW MFW -HPI(F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS COND/MFW End State: ATWS Conditional Probability: 3.OE-05 Event Identifier: 389/84-004 D-242
121 TRANS RT SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prob N Rec**
104 TRANS -RT -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI CV 1.5E-04 5.2E-01 112 TRANS -RT AFW MFW -HP! (F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS CV 3.3E-04
- b.IE-02
-COND/MFW 113 TRANS -RT AFW MFW -HPI(F/B) -HPR/--HPI PORV.OPEN -SS.OEPRESS CD 1.7E-04
- 3.1E-02 COND/MFW 114 TRANS -RT AFW MFW -HPI(F/B) -HPR/-HPI PORV.OPEN SS.DEPRESS CD 1.9E-05 9.2E-02 118 TRANS -RT AFW MFWHPI(F/B) -SS.DEPRESS -COND/MFW Cv 1.4E-05 3.2E-02 119 TRANS -RT AFW MFWHPI(F/8) -SS.DEPRESS COND/MFW CD 7.IE-06 1.6E-02 121 TRANS RT ATWS 3.OE-05 1 .2E-01
- dominant sequence for end state
- non-recovery credit for edited case MODEL: b:\pwrgtree.cmp DATA: b:\Iuciepro.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILIT IES Branch System Non-Recov Opr Fail TRANS 1.OE-03 1.OE+00 LOOP 2 .3E-05 3.4E-01 LOCA 2.6E-02 3 .4E-01 RT 2 .5E-04 1.2E-01 RT/ LOOP 0.OE+00 1.OE+00 EMERS .POWER 2.9E-03 5.1E-01 AFW 1.OE-03 > 5.9E-03 2.7E-01 Branch Model: I .OF.3+ser Train 1 Cond Prob: 2.OE-02 > Failed Train 2 Cond Prob: 1.0E-01 Train 3 Cond Prob: 5S..OE-02 Serial Component Prob: 9.2E-04 AFW/EMERS .POWER 5.OE-02 3.4E-01 MFW 1.9E-01 > 1.0E+00 3.4E-01 Branch Model: 1.OF.1 Train I Cond Prob: 1.9E-01 > Failed PORY .OR .SRV .CHALL 2.OE-02 1.OE+00 PORY .OR .SRV .RESEAT 1.0E-02 1.2E-01 PORV .OR .SRV .RESEAT/EMERG .POWER 1.0E-02 1.2E-01 SS .RELEAS .TERM 1.5E-02 > 1.0E+00 3.4E-01 > 1.0E+00 Branch Model: L.OF.1 Event Identifier: 389/84-004 D-243
Train I Cond Prob: 1.5E-02 > Failed 89 .RELEAS .TERtI/-MFW 1.5E-02 > l.OE+00 3.4E-01 > 1.OE+00 Branch Model: 1.O1'.1 Train I Couid Prob: 1.5E-02 > Failed 69 .DEPRESS 3.6E-02 1.OE+00 CONDIMFW 1.OE+00 3.4E-01 HPI 3.OE-04 5.2E-01 HPI (F/B) 3.OE-04 5.2E-01 4.E-02 PORY .OPEN I .OE+00 1.OE+00 HPR/-HPI 1 OE-03 1.OE+00 CSR 2.OE-03 3.4E-01
- forced Minarick
,04-12-1987
ý12:36:57 Event Identifier: 389/84-004 D-2 44