ML17266A398

LER 80-071/03L-0:on 801231,during Operation at 100% Power, Vol Control Tank Inadvertently Diluted,Leading to RCS Dilution,Increasing Power Above Tech Specs Limit.Caused by Failed Crosby Relief Valve V2173 on Acid Pump Discharge

ML17266A398
Person / Time
Site:	Saint Lucie
Issue date:	01/29/1981
From:	Pace P FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML17209A641	List: ML17209A640 ML17266A398
References
LER-80-071-03L, LER-80-71-3L, NUDOCS 8102180653
Download: ML17266A398 (3)

Text

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REPORTABLE OCCURRENCE 335-80-.71 LICENSEE EVENT REPORT PAGE TWO ADDITIONAI CAUSE DESCRIPT IOfl The chargino pumps'; which take suction on the YCT, pump..bora'ted water

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into the RCSfor boron concentration control and makeup. llhile blending boric acid and water to the VCT to slightly dilute the RCS and add make-up', a relief in the line to the blending valve failed. This returned the boric acic.'o the boric acid makeup f'ink instead of into the VCT.

This resulted in the dilution of the VCT and therefore the dilution of the RCZ.

The plant is designed to safely accomodate this transient but the event is potentially significant due to the misleading indication given. The relief valve is downstream from the boric acid flow element so the operators had indication of'a normal blend to the VCT. Due to the small amount of acid involved (a few gallons) and the large boric acid tank size (8,000 gallons), tank level did not respond with notice-able indication. Increasing power was the first indication of the transient and the cause was not readily apoarent. Since dilution via the VCT is a slow process, the transient had been in orogress for several minutes before there was any indication. An alternate boron injecticn path was used to reduce power.

The relief was disassembled and found to have a cut seat and a bent stem. Th seat was repaired and the stem replaced. The bent stem was the root cause of the dilution. How the stem became bent is unknown.

A review by Plant Operators of this LER and of the proper actions taken, will increase awareness of this problem and will help the operator to deal with similar events, should they occur in the future.

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