ML20149K388
| ML20149K388 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1984-015-00 | |
| Download: ML20149K388 (6) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 286/84-015 Event
Description:
LOOP with Both a DG Failure and an Unavailability Date of Event: November 16, 1984 Plant: Indian Point 3 EVENT DESCRIPTION Sequence On November 16, 1984, the reactor was at cold shutdown for a scheduled maintenance and inspection outage. RCS temperature was -.115*F with RIIR pump 32 providing core cooling. All plant electrical loads were being supplied from offsite 13.8-ky sources through the station auxiliary transformer (ST); 6.9-ky buses 5 and 6 were energized from the station auxiliary transformer via breakers ST-S and ST-6. All other inservice 6.9.-ky buses were energized via tie breakers to buses 5 and 6. EDG 31 was out of service for scheduled maintenan~ce. 'SWPs 31 through 36 were out of service to provide protection for divers cleaning the suction to the pumps on the intake structure. SWPs 38 and 39 and GCW pumps 31 and 32 were operating.
At 1242 h on November 16, breakers ST-S and ST-6 were tripped open via fault detection circuitry. A phase-to-phase fault had occurred as a piece of metal was blown onto the 138-ky primary-side A and B phase station auxiliary transformer buswork from an adjacent building roof.
As breakers ST-S and ST-6 opened, normal offsite power to the plant was lost. DGs 32 and 33 started automatically due to the undervoltage con-dition on their respective 480-V buses (6A and 5A) and achieved normal operating voltage. DG 33 successfully reenergized bus 5A, automatically starting CCW pump 31. The output breaker, 52-EG2, for DG 32 did not close, leaving bus 6A deenergized.
The control room operators closed breakers GT-35 and GT-36 at 1256 h to reenergize 6.9-kV buses 5 and 6 from the 13.8-kV offsite sources. Four-hundred-eighty-volt buses 2A and 3A were then manually energized via normal supply and tie breakers. RHR pump 31 was started manually to reestablish core cooling. Attempts to energize 480-V bus 6A by closing the station service transformer (SST) supply breaker SST-6 were unsuccessful due to an apparent loss of dc control power to the breaker. The operators then attempted to energize bus 6A from bus 3A by closing tie breaker 3AT6A. This breaker also failed to close. SW pump 38 was started manually to supply essential header cooling water. Both Event Identifier: 286/84-015 D-87
operating DGs were secured because offsite power had been successfully restored. After replacing failed control fuses, breaker SST-6 was closed, reenergizing 480-V bus 6A. All equipment was then returned to original status with the exception that outside power was being supplied by the 13.8-ky source instead of the normal 138-ky source. RCS tempera-0 ture increased ~-3 F during the time RHR was interrupted.
The total time that power was unavailable to the RUR system was 14 min. Because the reactor had been in the cold shutdown condition for over a month and Tavg was significantly below the 200*F limit for cold shutdown at the time of the event, the plant operators voluntarily chose to proceed cautiously and deliberately in restoring power. This was in light of the amount of equipment out of service at the time.
Corrective Action Investigation into the series of breaker failures associated with bus 6A has yielded the following results: (1) Breaker 52-EG2, the out-put breaker for DG 32, operated in accordance with design even though it did not close. Logic circuitry for the plant's electrical distribution system prevents any 480-V vital bus from being tied to two separate power supplies simultaneously. The bus 6A normal feed breaker, 52/6A, failed to open when offsite power was lost due to failed control power fuses. The logic circuitry therefore prevented breaker 52-EG2 from closing because two supply breakers to bus 6A would have been closed.
(2) Breaker SST-6, the SST supply breaker for bus 6A, opened as required on the LOOP. The control power fuses for this breaker are believed to have failed the previous time that the breaker was closed. The opera-tors were unable to close SST-6 until the fuses were replaced. (3) No cause for the failure of breaker 3A-6A was determined. The breaker worked properly the following day during testing.
On November 17, 1984, the events of the previous day were simulated to check the operation of all undervoltage associated equipment. As previously mentioned, new power supply fuses had been installed in breakers SST-6 and 52/6A. All equipment operated correctly. The roof from which the metal had fallen was inspected, and all remaining loose material was removed.
Plant/Event Data Systems Involved:
Emergency power Components and Failure Modes Involved:
One DG - unavailable due to routine maintenance One DG breaker - could not close on demand (logic failure)
Event Identifier: 286/84-015 D-8 8
Component Unavailability Duration: 1 d (assumed)
.Plant Operating Mode: 5 (0% power)
Discovery Method: Operational event Reactor Age: 8.6 years Plant Type: PWR Comments A bounding estimate was developed for this event. It assume's that the LOOP occurred while at power and that one DG was undergoing mainte-nance..
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP Base case Branches Impacted and Branch Nonrecovery Estimate.
Emergency power Base case *Degraded, two of three DGs unavailable AFW Base case *Degraded, one train unavailable HPI Base case Degraded, one train unavailable RPR Base case Degraded, one train unavailable LPI Base case Degraded, one train unavailable LPR Base case Degraded, one train unavailable Plant Models Utilized PWR plant Class B Event Identifier: 286/84-015 D-89
CONDITIONAL CORE WAGIAE PROBABILITY CALCULATIONS Event Identifier: 286/84-015 Event
Description:
LOOP with both a D65 Failure and an Unavailability Event Date: 11/16/84 Plant- Indian Point 3 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 3.E-01 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV LOOP 5.OE-05 Total 5.OE-05 CD LOOP 1.9E-04 Total 1.9E-04 ATWS LOOP O.OE+OO Total o.OE+OO DOMINANT SEQUENCES End State: CV Conditional Probability: 4.E-05 217 LOOP -RT/LOOP EMERS .POWER -AFW/EMER6 .PGWER -PORY .OR .SRV .CHALL SS .RELEAS .TERII End State: CD Conditional Probability: 1.7E-04 218 LOOP -RT/LOOP EMERG.POWER AFW/EtiERG.POI4ER SEQUENCE CONDITIONAL PROBABILITIES Event Identifier: 286/84-015 I>-90
Sequence State . Prob SeuneEnd NRec**
213 LOOP -RT/LOOP -EMERI3.POWER AFW -HPI(F/B) HPR/-HPI CD 9 .2E-06 ,5,dE-02 214 LOOP -RT/LOOP -EMERG.POWER AFW HPI(F/B) CD 7.OE-06 '4.7E-02 215 LOOP -RT/LOOP ElIERG.POt4ER -AFW/EMERt3.POWER PORV.OR.SRY.CHALL CV 2.OE-O6 :5.8E-02
-PORV .OR .SRV .RESEAT/EMERG .POI4ER 65 .RELEAS .TERM 217 LOOP -RT/LOOP EMERS .POWER -AFW/EMERG .POWER -PORV .OR .SRV .CHALL cv 4 .8E-05
- 5.9E-02
- dominant sequence for end state 4*non-recovery credit for edited case MODEL: b:\pwrbtree .cmp DATA: b:\IPPROB.CMP No Recovery Limit BRANC FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.OE-03 1.0E+00 LOOP 2.3E-05 3.4E-01 LOCA 4.2E-06 3.4E-01 RT 2.5E-04 1.2E-01 RT/LOOP O.OE+00 1.0E+00 Elf R6.POWER 2.9E-03 > 5.7E-02 5.1E-01 Branch Model: 1.OF .3 Train I Cond Prob: 5.OE-02 > Failed Train 2 Cond Prob: 5.7E-02 Train 3 Cond Prob: 1.9E-01 > Unavailable AFI4 1.OE-03 > 1.9E-03 2.7E-01 Branch Model: 1.OF.3+ser Train 1 Cond Prob: 2.OE-02 Train 2 Cond Prob: 1.OE-01 > Unavailable Train 3 Cond Prob: 5.OE-02 Serial Component Prob: 9.2E-04 AFW/EMERG.POWER 5.OE-02 3.4E-01 MFW 2.OE-01 3.4E-01 PORY iR.SRV .CHALL 4.OE-02 1.0E+00 PORV.OR.SRV.RESEAT 2.OE-02 5.OE-02 POR .OR .SRV .RESEAT/EMERG .POWER 2.OE-02 5.OE-02 SS.RELEAS.TERM 1.5E-02 3.4E-01 65 .RELEAS .TERM/-MFW 1.5E-02 3.4E-01 HPI 1.5E-03 > 2.2E-03 5.2E-01 Branch Model: 1.OF.3+ser Train I Cond Prob: 1.OE-02 Train 2 Cond Prob: 1.OE-O1 Event Identifier: 286/84-015 D-9 1
Train 3 Cofid Prob: 3.OE-01 ) Unavailable Serial Component Prob: 1.2E-03 HPI(F/B) 1.5E-03 > 2.2E-03 5.2E-01 4.OE-02 Branch Model: 1.OF.3+ser+opr Train 1 Cand Prob: 1.OE-02 Train 2 Cond Prob: 1.OE-01
.Train 3 Cond Prob: 3.OE-01 > Unavailable Serial Comnponent Prob: 1.2E-03 HPR/-HPI 3.OE-03 > 3.OE-02 5.6E-01 4.OE-02 Branch Model: 1.OF.2+opr Train 1 Cond Prob: 3.OE-02 Train 2 Cond Prob: 1.OE-01 > Unavailable PORY .OPEN 1.OE-02 1.OE+00 SS.DEPRESS 3.6E-02 1.OE+00 COND/MFW 1.OE+00 3.4E-O1 LPI/lfPI 1.OE-03 > 1.OE-02 3A.E-01 Branch Model: 1.fF.2 Train I Cond Prob: 1.OE-02 Train 2 Cond Prob: 1.OE-01 > Unavailable LPR/-HPI .HPR 6.7E-01 1.OE+00 LPR/HPI 1.OE-03 > 1.OE-02 I.OE+00 Branch Model: 1.7F.2 Train 1 Cond Prob: 1.OE-02 Train 2 Cond Prob: 1.OE-01 > Unavailable
- forced Minarick 04-11-1987 14:59:46 Event Identifier: 286/84-015 D-9 2