ML20149K490

Final ASP Analysis - Oconee 3 (LER 287-85-002)

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.

756E-06

2.

756E-06 CD LOOP Total

7.

132E-06

7.

132E-06 ATWS LOOP Total

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.

332E-08

4.

592E-042

3. 923E-07

5. 842E-04

4. 156E-071 7.707E-04 1.521E-06~

2.80BE-06 2.975E-06

3.

456E-07

1.

221E-06

4.

597E-02

3.

155E-03

4.

162E-03

4.

457E-02

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.

2B0E-05

4.

170E-06

2.

500E-04

0.

000E+00

5.

415E-04

1.

020E-03

5.

000E-012

1.

900E-01

4.

00E -02'

2.

000E-02 1.500E -02 1.500E-02

3.

600E-02

1.

000E+00

2.

29?E-03

2.

299E-03

0.

000E+00

1.

OO0E+00 3.400E-01 > 2.600E-01

3.

400E-01

1.

200E-01 1.000E+00 5.100E-Ol

2.

700E-01

3.

400E-01 3.400E-01 1.0O0E+00

5.

000E-02

3.

400E-01

3.

400E-01

1.

000E+00

3.

400E-01

5.

200E-01

5.

200E-01

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