ML19274E789

LER 79-040/03L-0 on 790326:during Steady State Operation, Periodic Calibr Revealed Nonconservative Overtemp Delta T Protection Circuitry Output.Caused by Instrument Drift. Summing Amplifier Card Replaced & Circuitry Recalibr

ML19274E789
Person / Time
Site:	North Anna
Issue date:	04/19/1979
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19274E784	List: ML19274E783 ML19274E786 ML19274E789
References
LER-79-040-03L, LER-79-40-3L, NUDOCS 7904240415
Download: ML19274E789 (2)

Text

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NAME OF PREPAREH

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Virginia Electric and Power Company North Anna Power Station, Unit #1

Attachment:

Page 1 of 1 Docket No. 50-338 Report No. 79-40/ 03L-0 Description of Event On 3/26/79 at approximately 1015, an instrument calibration " check" procedure was performed on the Channel I circuitry of Overtemperature delta T protection. The result of this procedure was the discovery of a non-conservative upper / lower flux summing amp output which effectively raised the overtemperature delta T setpoint.

Probable Consequences of Occurrence The overtemperature delta T channel is part of the reactor trip system.

instrumentation which ensures the reliability, redundance and diversity in the facility design for the protection and mitigation of accident and transient conditions. Therefore, this type of event is considered in the equipment design which provides protection for the safety and health of the general public.

Cause of Occurrence The cause of this occurrence is believed to be instrument drift.

Immediate Corrective Action The immediate corrective action was to replace the upper / lower flux signal summing amplifier (NM-412A) and recalibrate this card as per the appropriate instrument calibration procedure.

Scheduled Corrective Action No further action is required.

Actions Taken To Prevent Recurrence No action other than normal calibration surveillance is considered necessary.

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