ML20156A250
| ML20156A250 | |
| 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 1984-011-00 | |
| Download: ML20156A250 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 389/84-011 Event
Description:
Trip and One AFW Train Fails Date of Event: November 21, 1984 Plant: St. Lucie 2 EVENT DESCRIPTION Sequence At 0927 h on November 21, 1984, the reactor was automatically tripped from 68% power due to loss of load. The loss of load was due to a generator exciter field failure. All automatic functions performed as designed with the exception of the "C" auxiliary feed pump that received its start signal, attempted to start, and tripped on overspeed as a re-sult of steam leakage, causing the pump to spin. The B" auxiliary feed pump functioned properly and provided the needed feed flow to the SGs.
The cause of the overspeed trip was the pump spinning as a result of steam leakage. The leakage was corrected, and the pump spinning stopped.
The cause of the loss of field excitation was determined to be failure of the exciter bearing, which allowed the rotor to drop slightly and rub the permanent magnet generator.
Corrective Action The bearing and the permanent magnet generator were replaced.
Alignment and other checks were performed. No cause for the failure of the bearing was able to be determined. The AFW leakage was repaired.
Plant/Event Data Systems Involved:
AFW Components and Failure Modes Involved:
One AFW pump - failed on demand Component Unavailability Duration: NA Plant Operating Mode: 1 (68% power)
Discovery Method: Operational event Reactor Age: 1.4 years Plant Type: PWR Comments None Event Identifier: 389/84-011 D-245
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate-Transient 1.0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate
- MFW 0.34 Assumed failed AFW 0.27 Degraded; one train failed Plant Models Utilized PWR plant Class G Event Identifier: 389/84-011 D-246
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 389/84-011 Event
Description:
Trip and One AFW Train Fails Event Date: 11/21/84 Plant: St Lucie 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OE+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 3.5E-04 Total 3.5E-04 CD TRANS 2.OE-04 Total 2.OE-04 ATWS TRANS 3.OE-05 Total 3.DE-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 3.E-04 112 TRANS -RT AFW MFW -HPI(F/B) -HPRI-HPI PORV.OPEN -SS.DEPRESS -COND/tIFW 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-Oil D--247
121 TRANS RT SEQUENCE CONDITIONAL PROJBABILIT'IES Sequence End State Pr'ob N Rec**
112 TRANS -RT AFW MFW -HP! (F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS CV 3.3E-04
- 6.1E-02
-COND/MFW 113 TRANS -RT AFW MFW -HP! (F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS CD 1.7E-04
- 3.1E-02 COND/MFW 114 TRANS -RT AFW MFW -HP! (F/B) -HPR/-HPI PORV.OPEN SS.DEPRESS CD 1.9E-05 9.2E-02 118 TRANS -RT AFW ?IFWHPI(F/B) -SS.DEPRESS -COND/MFW CV 1 .4E-0.5 3.2E-02 119 TRANS -RT AFW MFWHPI(F/B) -SS.DEPRESS COND/MFW CD 7.I1E-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:\luciepro.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS I ,0E-03 1.0E+00 LOOP 2.3E-05 3.4E-01 LOCA 2 .6E-02 3.4E-01 RT 1.2E-01 RT/LOOP 0.OE+00 1.0E+00 EMERG.SPOWER 2.9E-03 5.1E-01 AFW 1.OE-03 > 5.9E-03 2.57E-01 Branch Model: 1.OF.3+ser Train I Cond Prob: 2.OE-02 > Failed Train 2 Cond Prob: 1 .0E-01 Train 3 Cond Prob: 5 .OE-02 Serial Component Prob: 9.2E-04 AFW/EMERG .POWER 5 .OE-02 3 .4E-01 MFW 1.9E-01 > 1.0E+00 3.4E-01 Branch Model: 1.OF.1 Train 1 Cond Prob: 1.9E-01 > Failed POR V.OR.SR V.CHALL 2.OE-02 1.0E+00 PORV .OR .SRV .RESEAT 1.OE-02 1.2E-01 PORY .OR .SRV .RESEAT/EMERG.SPOWER 1.OE-02 1.2E-01 SS .RELEAS STERM 1.5E-02 3 .4E-01 55 .RELEAS .TERM/-MFW 1.5E-02 3.4E-01 SS.SDEPRESS 3 .6E-02 1.0E+00 Event Identifier: 389/84-011 D-248
COND/MFW 1.OE+0O 3.E-01 HPI 3 .OE-04 5 .2E-01 HPI (F/B) 3. OE-04 5.2E-01 4 OE-02 PORY .OPEN 1.OE+00 1.OE+00 HPR/-HPI 1.OE-03 1.OE+00 CSR 2 .OE-03 3.E-01
- forced
- Minarick 04-12-1987
- 12:39:29 Event Identifier: 389/84-011 D- 249