05000346/LER-1979-005-03, /03L-0 on 790106:during Surveillance Testing, Borated Water Storage Tank Level Bistable Was Tripped;Valves DH9A Opened & DH7A Closed.Caused by Component Failure of Output Relay K51A & Instrument Drift

/03L-0 on 790106:during Surveillance Testing, Borated Water Storage Tank Level Bistable Was Tripped;Valves DH9A Opened & DH7A Closed.Caused by Component Failure of Output Relay K51A & Instrument Drift

ML19273B137
Person / Time
Site:	Davis Besse
Issue date:	01/31/1979
From:	Nelson J TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19273B134	List: 05000346/LER-1979-005, Forwards LER 79-005/03L-0 05000346/LER-1979-005-03, /03L-0 on 790106:during Surveillance Testing, Borated Water Storage Tank Level Bistable Was Tripped;Valves DH9A Opened & DH7A Closed.Caused by Component Failure of Output Relay K51A & Instrument Drift
References
LER-79-005-03L, LER-79-5-3L, NUDOCS 7902060383
Download: ML19273B137 (3)

LER-1979-005, /03L-0 on 790106:during Surveillance Testing, Borated Water Storage Tank Level Bistable Was Tripped;Valves DH9A Opened & DH7A Closed.Caused by Component Failure of Output Relay K51A & Instrument Drift

Event date:
Report date:
3461979005R03 - NRC Website

text

U. S. NUCLE AR REGUL ATORY CO.1. I NRC F pnM 366 (7 77).

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8 EVENT DESCRIPTION AND PROBABLE CC'.SECUENCES h of surveillance testing when the Borated Water Storage Tank (BWST)]

l o 12 l l During the conduct fo 13 l l level bistable was tripped, Decay Heat (DH) Valves DH9A opened and DH7A closed. The [

l Lvalves were returned to nornal and the breakers for these valves were opened to pre-o

.i further inadvertent actuations and thus naintain the flowpath fron the BWST to l

o 3 l vent 3 6 l Energency Core Cooling Systen (ECCS) Train 2.

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ECCS Train 1 was fully I

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CAUSE DE3CRIPTION AND CORRECTIVE ACTIONS h failure of output relay

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l, j i j l K51A in Safety Features Actuation Systea (SFAS) Channel 4.

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l believed to be the cause of BWST level bistable being out of tolerance.

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The bistable was recalibrated as per the test procedure to withig i.

l the Tech Spec limits. The bistable will be replaced during an upconing outage.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POLER STATION UNIT ONE SUPPLEMENTAL INFOPJ1ATION FOR LER NP-33-79-06 DATE OF EVENT: January 6, 1979 i

FACILITY: Davis-Besse Unit 1 Saf ety Features Actuation System (SFAS) Channel 4 IDENTIFICATION OF OCCURRENCE:

output relay f ailure and Channel 2 Borated Water Storage Tank (BWST) level setpoint out of tolerance f

The unit was in Mode 1, with Power (MWT) = 2747, Conditions Prior to Occurrence:

and Load (Gross MWE) = 915.

Description of Occurrence: During the conduct of Step 6.5 of Surveillance Test ST 5031.01, "SFAS Monthly Test" on January 6, 1979, at 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, BNST level bi-stable BA212 was tripped as per the test procedure. Upon tripping BA212, Decay Heat (DH) Valve DH9A, " Emergency Sump Outlet Line 2 Isolation Valve", opened and DH7A, "BWST Outlet Isolation Valve" closed. The bistable was reset as per the procedure of ST 5031.01, and DH9A was reclosed and DH7A, "BWST Outlet Isolation Valve" (which is interlocked with DH9A tc close when DH9A opens) was reopened.

investigation into the cause of DH9A opening (and DH7A closing)

During the subsequent further inadvertent actua-the breakers for these two valves were opened to prevent tions and thus maintain the flowpath from the BWST to Emergency Core Cooling System (ECCS) Train 2.

However, removing power from the operators of these valves also disables the automatic transfer to the caergency sump.

This placed the unit in the Action Statement of Technical Specification 3.5.2, which requires two (2) operable ECCS trains in Mode 1.

After the problem which caused the actuation of DH9A was found and resolved, Step 6.5 of ST 5031.01 was re-performed unsuccessfully.

It was found that the setpoint of BWST level bistable BA212 was in excess of the Technical Specification limit of 4.725 feet of BWST level. This placed the unit in Action Statement 9 of Technical Specification 3.3.2.1.

Designation of Apparent Cause of Occurrence:

The cause of the actuation of DH9A and DH7A was component f ailure of output relay K51A in SFAS Channel 4.

Tripping BA212 in addition to the f ailare of relay K51A caused the two out of four logic to be satisfied and thus actuate DH9A and DH7A.

Instrument drift is believed to be the cause of BWST level bistable BA 212 being out of tolerance.

LER //79-005

TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE PAGE 2 SUPPLEMENTAL INFOMRATION FOR LER NP-33-79-06 There was no danger to the health and safety of the public Analysis of Occurrence:

or to unit personnel. The flowpath from the BWST to ECCS Train 2 was returned to Thus ECCS Train 2 was capable of operability when DH9A was closed and DH7A opened.

performing its safety function in the event of an accident until the BWST was emptied.

ECCS Train 1 was fully operable throughout the occurrence.

Under Maintenance Work Order (MWO) IC-119-79, Instrument and

Corrective Action

Control personnel investigated, found, and corrected the cause of DH9A and DH7A actuation.

An output relay, K51A in SFAS Channel 4 was defective and was replaced.

Upon finding the BWST level bistable BA212 out of calibration, it was immediately (ST 5031.01) procedure, to within the Technical Speci-recalibrated as per the test The breakers to DH9A and DH7A were cl' sed, restoring ECCS Train 2 o

fication limits.

to full operability.

SEAS Channel 2, BWST level trip was declared operable at 0100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> on January 6, 1979, thus removing the unit from the Action Statement of Technical Specification 3.5.2 and Technical Specification 3.3.2.1.

Since bistable BA212 has jrifted in the the same direction on a previous occasion (see Licensee Event Report NP-33-78-133),

bistable will be replaced during an upcoming maintenance outage.

It is estimated that approximately 6300 gallons of water flowed into the containment energency sump during the time DH9A was open.

This water flowed through the contain-ment and emergency suap drains to the containment normal sump uhere it was pumped to the Miscellaneous Waste Drain Tank. The area surrounding the emergency sump was inspected and no execssive contamination was present. The post accident boric acid neutralizinn baskets were inspected and no evidence of penetration was discovered.

Failure Data: There have been no previous f ailures of output relays.

Two previous incidents of BUST level bistables being out of tolerance were reported in Licensee Event Reports NP-33-78-84 and NP-33-78-13.

LER #79-005