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Final ASP Analysis - Catawba 1 (LER 413-85-041)
	ML20147A493
Person / Time
Site:	Catawba
Issue date:	05/26/2020
From:	Christopher Hunter; Office of Nuclear Regulatory Research
To:	;
	Littlejohn J (301) 415-0428
References
	LER 1985-041-00
	Download: ML20147A493 (5)
	v • d • e

PRECURSOR DESCRIPTION AND ANALYSIS LER No.:

413/85-041 Event

Description:

LOFW and Secondary-Side Relief Valve Problems Date of Event:

June 13, 1985 Plant:

Catawba 1 EVENT DESCRIPTION Sequence After declaring an Unusual Event at 2145 h because of unidentified RCS leakage, reactor power was reduced to 15%.

MNW pump A was secured.

At this power level, the feedwater flow path was switched from the lower feedwater nozzles to the upper ANW nozzles.

During the changeover a low-suction flow trip of MFW pump B occurred, causing a turbine trip and an autostart of both AFW motor-driven pumps and MFW isolation.

The reactor was subsequently manually tripped from 6% power as required by the loss of SG feedwater abnormal procedure.

The pressurizer PORVs opened and closed on high pressure within 2 s. SG P.ORV "C" opened for 1.5 min. The PORVs in the other three SGs failed to open on demand.

The safety-grade MSRVs were operational.

The MNW pump trip occurred during a flow reduction caused by a normal plant shutdown sequence.

The MFW pump B recirculation valve was not capable of modulating quickly enough to provide adequate pump minimum flow, causing its trip.

An attempted restart of pump B failed.

Corrective Action SG PORVs were recalibrated to open at proper set points.

Procedures were revised to provide guidelines for manual control of the feedwater minimum flow valves during nozzle changeover to ensure minimum pump flow.

Plant/Event Data Systems Involved:

Main steam relief (PORVs) and MFW Components and Failure Modes Involved:

MFW pump -

failed in operation Three SG PORVs -

failed on demand Event Identifier:

413/85-041 E-291

Component Unavailability Duration:

NA Plant Operating Mode:

1 (16% power)

Discovery Method:

Operational event Reactor Age:

0.5 year Plant Type:

PWR Comments See LER 413/85-043 on June 22, 1985, for a similar event MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Non recoverable Branches Impacted and Branch Nonrecovery Estimate MFW 0.34 Restart of pump B failed, so the nonrecovery estimate reflects the difficulty of restarting the system or pump B or restarting pump A during the transient The three failed SG PORVs were not readily recoverable (recoverable only

locally, if at all);

turbine bypass valves were still available for depressurization Secondary-side depressurization 0.34 Plant Models Utilized PWR plant Class F Event Identifier:

413/85-041 E-292

LER Number:

Event

Description:

Event Date:

Plant:

CONDITIONAL CORE DAMAGE CALCULATIONS 41,3185-041 LOFW and Secondary Side Relief Valve Problems Catawba I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator CV TRANS Total

1.

OOOE+00 Probability

6.

871E-06

6.

871E-06 CD TRANS Total

6.

698E-06

6.

69BE-06 ATWS TRANS Total DOMINANT SEQUENCES End State:

CV Conditional Probability:

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

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

ATWS Conditional Probability:

128 TRANS RT

3.

OOOE-05

3.

OGOE-05 2.5~45E-06

1.

2B9E-06

3.

OOOE-05 Event Identifier:

413/B5-041 E-2 93

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

181 TRANS -RT -AFN PORV.OR.SRV.CHALL -PORV.OR.SRV.RESEAT SS.RELE AS.TERM HPI 102 TRAN -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP RI-HP! -SS.DEPRESS -LPRI-HPI.HPR 103 TRANS -RI -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HP! HP RI-HP! -SS.DEPRESS LPRI-HPI.HPR 104 TRANS -RI -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HP! HP Ri-HP! SS.DEPRESS 109 TRANS -RI -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI 119 TRANS -RI AFW MFW -HPI(FIB) -HPRI-HPI PORV.OPEN -SS.DEPRESS

-CONDIMFW 1240 TRANS -RT AFN MFW -HP!(FIB) -HPRI-HPI PORV.OPEN -SS.DEPRESS CONDIMFW Cv CD CD CV CV CO

1.

1.

5.

1.

1.

103E-06 1.956E-03

8.

482E-07

1.

008E-070 4.545E-06 *1.76BE-01 31.750E-07 3.681'E-02 1.932E-07 13897E-02 122 123 124 125 1 26 127 128 TRANS -RT TRANS -RT TRANS -RT TRANS -RT TRANS -RI TRANS -RI TRANS -RT TRANS RI AFW AFW AFW AFW AFW AFW AFW MFW MFW MFW MFW MFW MFW MFW

-HP! (F/B)

-HP! (FIB)

HPI (F/B)

HP! (FIB)

-HPRi-HPI PORV.OPEN HPRI-HPI -SS.DEPRESS HPRI-HPI -SS. DEPRESS HPRI-HPI SS. DEPRESS

-SS.DEPRESS -CONOINFW

-SS. DEPRESaS COND/MFW SS. DEPRESS SS. DEPRESS

-CONDIMFW CON D/MFW CD CV Cc CD Cv CD CD AIWS

2. 927E-07

1.

62SE-06

8.