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Final ASP Analysis - Oconee 1 (LER 269-85-002)
	ML20149K484
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: ML20149K484 (5)
	v • d • e

PRECURSOR DESCRIPTION AND ANALYSIS LER No.:,

269/85-002 Event

Description:

Spurious Main Steam Intercept Valve Closure and Trip Date of Event January 22, 1985 Plant:

Oconee 1 EVENT DESCRIPTION Sequence On January 22, 1985, at 0447 h, Oconee Unit 1 tripped from 100% full power.

The trip occurred when all six intercept valves closed for unknown reasons, causing high turbine header pressure that resulted in high RCS pressure.

The reactor tripped on high RCS pressure -.5 s after the intercept valves closed and main steam relief valves (MSRVs) opened to relieve secondary side pressure.

MSRVs No. 2 and No. 10 failed to reseat until SG pressure had been reduced to 875 psig.

Two of six main steam valves.that supply main steam to moisture separator heaters were manually closed from the control room to help control main steam header pressure.

Because of previously identified control problems, the other four valves had been placed in the open position and could not be closed from the control room during the event.

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

Subsequent investigations found no problem or reasons to explain the intercept valve closures.

The unit was placed back on-line at 100% power at 2330 h.

Plant/Event Data Systems Involved:

Turbine intercept valves (TIV) and steam relief Components and Failure Modes Involved:

Mýa in s team i n ter cept val ves -

spuriously closed during operation Two MSRVs -

initially failed to reclose after opening Four of six main steam to moisture separator heater valves

-failed to close Component Unavailability Duration:

NA Plant Operating Mode:

100% power Discovery Method:

Operational event Reactor Age:

11.8 years Plant Type:

PWR Event Identifier:

269/85-002 E-8 1

Comments MSRVs 2 and 10 have behaved similarly as documented in LER 269/84-006.

See also LER 269/85-005 for a similar event.

(Ref. LERs84-006 and 85-005.)

MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate Steam-side re-0.12 MSRVs reseated in the required period lease terminated after reducing pressure from the control room Steam-side re-0.12 Rationale for recovery estimate same lease terminated; as above given MFW success Plant Models Utilized PWR plant Class D Event Identifier:

269/85-002 E-82

CONDITIONAL CORE DAMAGE CALCULATIONS LER Number:

Event

Description:

Event Date:

Plant:

269/85-002 Spurious Main Steam Intercept Valve Closure and Trip 1/22/85 Oconee I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator CV TRANS Total CD TRANS Total AIMS TRANS Total

1.

OOOE+OO Probability

2.

021E-05

2.

021E-05

1.

681 E-06

1.

681E-06

3.

OOOE -05

3.

OOOE -05 DOMINANT SEQUENCES End State:

CV Conditional Probability:

109 TRANS -RT -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI End State: CO Conditional Probability:

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

128 TRANS RT

1.

722E-05

1.

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

3.

OOOE-05 Event Identifier:

269/85-002 E-8 3

SEQUENCE CONDIT IONAL PROBABILITIES Sequence End State Seq. Prob Non-Recovil 101 TRANS -RT -AFW PORV.OR.SRV.CHALL -PORV.OR.SRV.RESEAT SS.RELE AS.TERM HPI 102 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP R/-HPI -SS.DEPRESS -LPR/-HPI.HPR 103 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP R/-HPI -SS.DEPRESS LPR/-HPI.HPR 104 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP R/-HPI SS.OEPRESS 109 TRANS -RI -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI 123 TRANS -RI AFW PIFW

-HPI(F/B) HPR/-HPI -SS.DEPRESS COND/NFW 126 TRANS -RI AFN MFW HPI(F/B) -SS.DEPRESS CONDIIIFN 128 TRANS RI CV CV CD CD

1.

496E-06

6.

240E-02

5.

273E-07

2.

964E-03 1.075E-06

2.964E-03

5.

989E-08

2.

964E-03 CV CD CO ATWS 1.722E-05

2.45 1E-07

2.

464E-07 3.OOOE-05 f

6.

240E-02

1.

776E-03

1.

302E -03

1.

200E-01I Idominant sequence for end state IInon-recovery credit for edited case Note:

Conditional probability values are differential values which reflect the added risk due to failures associated with an even~t.

Parenthetical values indicate a reduction in risk compared to a simil'ar period without the existing failures.

MODEL:

DATA:

b

pwrdtree. cup b: oconprob. cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS LOOP LOCA RI RI/LOOP EMERG. POWER AFN AFK/EMERG. POWER "FM PORV. OR. SRV. CHALL PORV. OR. SRV. RESEAT PORV. OR.SRV. RESEAT/ENERD. POWER SS. RELEAS. TERM Branch Model:

1.OF.1 Train I Cond Prob:

Event Identifier:

269/85-002

1.

2.

4.

2.

0.