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Final ASP Analysis - Oconee 1 (LER 269-85-005)
	ML20149K485
Person / Time
Site:	Oconee
Issue date:	05/28/2020
From:	Christopher Hunter; NRC/RES/DRA/PRB
To:	;
	Littlejohn J (301) 415-0428
References
	LER 1985-005-01
	Download: ML20149K485 (5)
	v • d • e

PRECURSOR DESCRIPTION AND ANALYSIS LER No.:

269/85-005 Rev. 1 Event

Description:

Two Stuck-Open Steam Generator Relief Valves Date of Event:

April 11, 1985 Plant:

Oconee 1 EVENT DESCRIPTION Sequence On April 11, 1985, at 1228 h, Oconee 1 tripped from 100% full power upon the fast closure of the low-pressure Turbine Intercept Valves and the main turbine control valves.

The resulting higher turbine header pressure and reduced heat transfer caused a turbine trip and subsequent RCS pressure rise until the reactor trip set point was reached.

The trip occurred.-

4 s (1228 h) after the valves closed.

Main steam relief valves (MSRVs) 4 and 10 opened for steam relief.

MFW flow was maintained.

The PORVs were not challenged.

HPI was utilized for a short period for inventory control.

MSRVs 4 and 10 failed to reclose until steam generator pressure was reduced to 880 psig.

Corrective Action The immediate corrective action was to stabilize the unit at hot shutdown conditions.

The subsequent investigation resulted in the discovery of a faulty edge connector on a circuit board in one of the electrohydraulic control cabinets.

Following the repair of the connector, the unit was put back in operation.

Plant/Event Data Systems Involved:

Steam relief, turbine intercept valves, HPI Components and Failure Modes Involved:

Two MSRVs -

failed to close TG EH-C card -

failed in operation HPI -

isolated too soon HPI supply valve -

failed to open from control room on demand Component Unavailability Duration:

NA Plant Operating Mode:

100% power Discovery Method:

Operational event Reactor Age:

12.0 years Plant Type:

PWR Event Identifier:

269/85-005 E-86

Comments A similar trip occurred January 22, 1985, and is described in LER 269/85-002.

Description:

Event Date:

Plant:

-CONDITIONAL CORE DAMAGE CALCULATIONS 269/85-005 Rev.1 Two Stuck Open Steam Generator Relief Valves 4/11/85 Oconee I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator CV TRANS Total CD TRANS Total ATWS TRANS Total

1.

000E+00 Probability 2.021IE-05

2.

021E-05

1.

68 IE-06 1.68 1E-06

3.

OOOE-05

3.

OOOE-05 DOM INANT SEQUENCES End State:

CV Conditional Probability:

109 TRANS -RT -AFN -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI End State:

CD Conditional Probability:

103 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI End State: ATHS Conditional Probability:

128 TRANS RT

1.

722E-05

1.

075E-06 HPR/-HPI -SS.DEPRESS LPR/-HPI.HPR

3.

OOOE -05 Event Identifier: 269/85-005 Rev.1 E-88

SEQUENCE CONDI TIONAL PROBABILIT IES Sequence End State Seq. Prob Non-Recovif 101 TRANS -RI -AFW PORV.OR.SRV.CHALL -PURV.OR.SRV.RESEAT SS.RELE AS.TERM HPI 102 TRANS -RI -AFWf PORV.OR.SRV.CHALL PORV.DR.SRV.RESEAT -HP! HP RI-HPI -SS.DEPRESS -LPR/-HPI.HPR 103 TRANS -RI -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP RI-HP! -SS.DEPRESS LPRI-HPI.HPR 104 TRANS -RI -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP RI-HP! SS.DEPRESS 109 TRANS -RI -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERN HP!

123 TRANS -RI AFN MFW -HPI(FIB) HPRI-HPI -SS.DEPRESS CONDINFW 126 TRANS -RI AFW NFW HPICFIB) -SS.DEPRESS COND/NFW 128 TRANS RI CY Cv CD

1.

496E-06

6.

240E-02

5. 2Y3E-07

2. 964E-03 1..075E-06

2.964E-03

5.

989E-OB

2. 964E-03 CD Cv CD CD ATWS 1.722E-05 *

2.

451E-07

2.

464E-07 3.OO0E-05 *

6. 240E-02

1.

776E -03

1. 302E -03

1.

200E-01

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 failures associated with an event.

Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.

MODEL:

DATA-b: pwrdtree. cmp b.-oconprob.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS LOOP LOCA RI RI/LOOP EMERS. POWER AFW AFW/ENERS. POWER FNF PORY. OR. SRV.CHALL PORV. OR. SRV. RESEAT PORV. OR.SRV. RESEAT/EMER6. POWER SS. RELEAS. TERM Branch Model: