ML20149K490
| ML20149K490 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-002-00 | |
| Download: ML20149K490 (5) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.:
287/85-002 Event
Description:
Lockout of Startup Transformer While Shut Down Date of Event:
August 28, 1985 Plant:
Oconee 3 EVENT DESCRIPTION Sequence on August 28, 1985, Unit 3 was in a refueling outage with its auxiliary power being supplied by startup transformer CT-3.
At 0340 h the fault pressure relay on the transformer actuated.
This initiated a lockout that cleared and deenergized the transformer.
Unit 3 main feeder buses 1 and 2 were deenergized, resulting in a loss of ac power.
Corrective Action The immediate corrective action was to supply auxiliary power to Unit 3 by Keowee Hydro Units 1 and 2 via CT-4.
The load center transformer feeder breakers that tripped on loss of power were reset.
Auxiliary power load was transferred to CT-S.
An investigation was initiated to determine the reason for CT-3 fault pressure relay actuation and lockout.
CT-3 insulating oil was drained and cleaned.
Approximately 400 oz.
of water was removed from the transformer tank and windings.
The windings were inspected twice.
Three bad Y phase insulators on the 4.16-ky bus to CT-3 were replaced.
One bad neutral brushing for the winding was replaced.
Finally, the fault pressure relay was replaced.
Plant/Event Data Systems Involved:
4.16-ky auxiliary power Components and Failure Modes Involved:
Startup trans-former -
fault pressure. relay Component Unavailability Duration:
NA Plant Operating Mode:
Refueling Discovery Method:
Operational event Reactor Age:
11.1 years Plant Type:
PWR Comments None Event Identifier:
287/85-002 E-125
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP 0.26 Base case (0.34) x assumed probability of occurring at power (0.75)
Branches Impacted and Branch Nonrecovery Estimate None Plant Models Utilized PWR plant Class D Event Identifier:
287/85-002 E-126
LER Number:
Event
Description:
Event Date:
Plant:
CONDITIONAL CORE DAMAGE CALCULATIONS 287185-002 Lockout of Startup Transformer While Shutdown 8/28/85 Oconee 3 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP
- 2.
600E-0 I SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV LOOP Total
- 2.
- 2.
- 7.
- 7.
- 0.
000E+00
- 0.
000E+00 DOMIINANT SEQUENCES End State:
CV Conditional Probability:
1.521E-06 212 LOOP -RT/LOOP -EP -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI End State:
CD Conditional Probability:
2.975E-06 215 LOOP -RT/LUOP -EP AFW -HPI HPR/-HPI SEQUENCE CONDITIONAL PROBABILITIES Event Identifier: 287185-002 E-127
Sequence SeueceEnd State Seq. Prob Non-Recov**
201 LOOP -RI/LOOP -EP -AFN PORV.OR.SRV.CHALL -PURV.OR.SRV.RESEAT SS.RELEAS.TERM HP!
202 LOOP -RI/LOOP -EP -AFN PORV. OR. SRY. CNALL PORY. OR. SAY.RESEAT
-HP! -HPR/-HPI CSR -SS.DEPRESS -LPR/-HPI 205 LOOP -RI/LOOP -EP -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT
-HP! HPR/-HPI -SS.DEPRESS -LPR/-HPI 212 LOOP -Ri/LOOP -EP -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI 214 LOOP -RTILOOP -EP AFW -HP! -HPR/-HPI CSR 215 LOOP -RT/'LOOP -EP AFW -HP!
HPR/-HPI 219 LOOP -RT/LOOP EP -AFW/EP -PORV.OR.SRV.CHALL SS.RELEAS.TERM 220 LOOP -AT/LOOP EP AFW/EP cv CY cv Cv CD CD CY ED
- 6.
- 4.
- 3. 923E-07
- 5. 842E-04
- 4. 156E-071 7.707E-04 1.521E-06~
2.80BE-06 2.975E-06
- 3.
- 1.
- 4.
- 3.
- 4.
- 4.
- 4.
50BE-02 1*non-recovery credit for edited case Note:
Conditional probability values are differential values which reflect the added risk due to observed failures.
Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.
MODEL:
B:pwrdtree.cmp DATA:
B:surrprob.cop No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS LOOP Branch Model:
INITOR Initiator Freq:
LOCA RI RI/LOOP EP AFW AFN/EP MFW PORY. OR.SRV.CHALL PORV. OR. SRV.RESEAT SS. RELEAS. TERN SS. RELEAS. IERI¶/-MFW SS. DEPRESS COND/MFW HP!
HPI(FIB)
PORY. OPEN Event Identifier: 287/85-002
- 1.
030E-03 2.280E-05 > 2.280E-05
- 2.
- 4.
- 2.
- 0.
000E+00
- 5.
- 1.
- 5.
- 1.
- 4.
00E -02'
- 2.
000E-02 1.500E -02 1.500E-02
- 3.
- 1.
000E+00
- 2.
29?E-03
- 2.
- 0.
000E+00
- 1.
OO0E+00 3.400E-01 > 2.600E-01
- 3.
- 1.
200E-01 1.000E+00 5.100E-Ol
- 2.
- 3.
400E-01 3.400E-01 1.0O0E+00
- 5.
- 3.
- 3.
- 1.
000E+00
- 3.
- 5.
- 5.
- 1.
OOOE+00
- 4.
OOOE-02 F,-1 28
HPR/-HPI 3.OOOE-03 5.600E-01 4.OOOE-02 CSR 3.OOOE-03 3.400E-01 4.OOOE-02 PORV.OPEN 1.OO0E-03 3.400E-01 LPI/HPI 6.700E-01 1.OOOE+00 LPR/-HPI 2.OOOE-03 1.OODE+00 LPR/HPI 0.OOOE+00 0.OOOE+00 if* forced Austini 08-13-1986 02: 09:44 Event Identifier: 287/85-002 E-129