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Final ASP Analysis - Trojan (LER 344-85-009)
	ML20161A154
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	06/09/2020
From:	Christopher Hunter; NRC/RES/DRA/PRB
To:	;
	Littlejohn J (301) 415-0428
References
	LER 1985-009-00
	Download: ML20161A154 (5)
	v • d • e

PRECURSOR DESCRIPTION AND ANALYSIS LER No.:

344/85-009 Event

Description:

AFW Pumps Fail on Demand Following Trip Date of Event:

July 20, 1985 Plant:

Trojan EVENT DESCRIPTION Sequence At 0707 h a short in a cooling fan caused a trip of the main cooling unit for the unit auxiliary transformer and overheating of the trans-former.

The entire transformer cooling system tripped rather than only the one affected fan.

The control room alarm failed.

The operators failed to notice another temperature indication.

This resulted in a turbine trip and a subsequent reactor trip.

AFW was demanded as plant conditions initiated MFW isolation.

Both AFW pumps started, but the diesel ANW pump tripped on low suction pressure.

The operator restarted the pump after blocking the trip, but then the turbine AFW pump tripped (3 to 5 min later),

also on low suction pressure.

The operator throttled down the AFW pump discharge valves and restarted the turbine pump satisfactorily.

Six hours after the reactor trip during restart, a condenser/circulating water leak was discovered but thought to be minor by the operators.

The plant was restarted but then later shut down when the severity of the leak was discovered.

Corrective Action The transformer cooling fan was repaired, and the AFW pump suction trip design problem was resolved.

Plant/Event Data:

Systems Involved:

AFW, transformer (cooling system), MEW Components and Failure Modes Involved:

AFW pumps -

failed on demand (sequentially)

Main condenser tube leak -

discovered during restart operation Component Unavailability Duration:

NA Plant Operating Mo'de:

1 (100% power)

Discovery Method:

During operation Reacto r Age:

9.59 years Plant Type:

PWR Event Identifier:

344/85-009 E-201

Comments The AFW pumps also tripped repeatedly during subsequent testing and investigation of the problem MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate AFW 0.04 Readily recoverable MFW Base case Note that MFW is modeled as unavail-able because of automatic isolation following transients involving each trip Plant Models Utilized PWR plant Class C Event Identifier:

344/85-009 E-202

CONDITIONAL CORE DAMAGE CALCULATIONS LER Number:

Event

Description:

Event Date:

Plant:

344/85-009 AFW Pumps Fail on Demand Following Trip 7/20185 Trojan INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator CV TRANS Total

1.

OOOE+00 Probability

7.

786E-04

7. 786E-04 CD TRANS Total

4.

445E-04

4.

445E-04 ATWS TRANS Total DOMINANT SEQUENCES End State: CV Conditional Probability:

125 TRANS -RT AFN MFW HPliF/B) -SS.DEPRESS -COND/MFW End State:

CD Conditional Probability:

126 TRANS -RT AFW RFW HPI(F/B) -SS.DEPRESS COND/MFW End State:

ATWS Conditional Probability:

128 TRANS RT

3.

OOOE-05

3.

OOOE-05

3.

504E-04

1. 805E-04

3.

000E-05 Event Identifier: 344/85-009 E-203

SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prob Non-Recovi*

119 TRANS -RT AFW MFW -HPI(FIB) -HPR/-HPI PORV.OPEN -SS.DEPRESS

-COND/MFW 120 TRANS -RI AFW MFW -HPI(FIB) -HPRI-HPI PORV.OPEN -SS.DEPRESS CONDIMFW 122 TRANS -RI AFN MFW -HPI(F/B) HPR/-HPI -SS.DEPRESS -CONDIMFN 123)

TRANS -RT AFW MFW -HPI(F/B) HPR/-HPl -SS.DEPRESS COND/MFW 124 TRANS -RT AFW MFW -HPI(F/B) I4PR/-HPI SS.DEPRESS 125 TRANS -RI AFN MFW HPI(F/8) -SS.DEPRESS -COND/MFW 126 TRANS -RT AFW MFW Hi(FfB) -SS.DEPRESS COND/MFW 127 TRANS -RT AFW flFW HPI(F/B) SS.DEPRESS 128 TRANS RI CV CD 7.957 E-05

8.

264E-03 4.099E-05

4.

257E-03 CY CD CD Cv CD CD AIWS

3.

455E-04

1.

7BOE-04

1.

955E-05 3.504E-04

1.80SE-04*

1.

983E-05

3.

OOOE-05

5.

107E-04 2.631E-04

7.

738E-04

4.

09SE-04 2.11 IE-04

6.

210E-04

1.

200E-01 4 dominant sequence for end state 4* 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:pwrbtree.cmp DATA:

b:trojprob.cmp No Recovery Limit BRANCH FREGUENC IES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS LOOP LOCA RI RI/LOOP EMERG. POWER AFW Branch Model:

1.OF.2 Train I Cond Prob:

Train 2 Cond Prob:

AFW/IEERG. POWER Branch Model:

1.OF.1 Train 1 Cond Prob:

MFW PORY. OR. SRV. CHALL PORY. OR.SRV.RESEAT Event Identifier: 344/85-009

1.

030E-03

2.

280E -05

4.

170E-06

2.