ML19312C216

Abnormal Occurrence AO-269/75-15:on 751219,borated Water Storage Tank Level Indication Failed.Caused by Failure of Trace Heating to Level Instrumentation Air Lines.Station Mod Initiated to Provide Power for Heat Tracing

ML19312C216
Person / Time
Site:	Oconee
Issue date:	01/07/1976
From:	DUKE POWER CO.
To:
Shared Package
ML19312C215	List: ML19312C214 ML19312C216
References
NUDOCS 7912100696
Download: ML19312C216 (2)

Text

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DUKE POWER COMPANY

, OCONEE UNIT 1 nr

' Report No.: A0-269/75-15 Report Date: January 7,1976 Occurrence Date: December 19, 1975 Facility: Oconee Unit 1, Seneca, South Carolina Identification of Occurrence: Failure of borated water storage tank level j indication Conditions Prior to Occurrence: Unit at 100%. full power Descrip". ion of Occurrence:

On December 19, 1975, both channels of the Oconee Unit 1 BVST level instrumentation failed as a result of freezing of moisture in the impulse lines to the level transmitters. Technica] Specification 3.3.1.8 requires that both channels of BWST level instrumentation be operable. Reactor power was immediately reduced and a shutdown initiated. Within 3.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, one level channel was put back into service by running a separate impulse line to the level transmitter. Reactor power had been decreased to 65%,

and the shutdown was terminated. Both channels were returned to service approximacely 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> later.

Apparent Cause of Occurrence:

The apparent cause of this occurrence was the failure of trace heating to the level instrumentation air lines. Consec,uently, the very low ambient air temperature (16 F) caused moisture er. trained in the lines to freeze, resulting in instrument failure. Investigation indicated that an electrical short had occurred in one of the trace heating lines. Since the two lines are connected in series, the other line was electrically open and also inoperable.

Analysis of Event:

Although there was no BWST level instrumentation for approximately 3h hours, the tank showed a normal level of 48 feet when indication was restored. No l leaks were detected, and it is concluded that the tank level remained normal l during the time that no indication was available. Therefore, adequate borated l water was available for HPI, LPI, and Reactor Building spray in the event of an Engineered Safeguards actuation. It is concluded that the health and safety of the public was not affected by this occurrence.

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• ').. -AQ-269/75-15 January 7, 1976 Page 2 Corrective Action:

A station modification was initiated to provide power for the heat tracing on each BWST level transmitter from an independent power source, thereby providing redundancy between the two heat tracing lines. This modification has been completed on the Unit 1 BWST heat tracing and will be implemented on Units 2 and 3 by March 15, 1976.

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