05000338/LER-1979-040-03, /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

/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: 05000338/LER-1979-039-03, /03L-0 on 790325:during Normal Operation,Power Supply to Hydrogen Recombiner Deenergized & Recombiner Inoperable for 10-h.Unit 2 Emergency Bus Degraded Voltage Protection Modified & Reenergized 05000338/LER-1979-040-03, /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 ML19274E783
References
LER-79-040-03L, LER-79-40-3L, NUDOCS 7904240415
Download: ML19274E789 (2)

LER-1979-040, /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

Event date:
Report date:
3381979040R03 - NRC Website

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U.S. NUCLE AR REGUL ATORY COMMISSION NRC F ORM 366 om LICENSEE EVENT REPORT CONTROL DLOCK: l l

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63 EVENT DATE 14 75 REPOR T D ATE bo E VENT DESCRIPTION AND PROBABLE CONSEQUENCES h l On 3/26/79 during normal steady state operation, a periodic calibration procedure I

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I was performed on the Overtemperature Delta T protection circuitry.

This procedure I

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lo l41 [ revealed a nonconservative output of the upper / lower flux signal summing amplifier in 1 10l5l l the Overpower Delta T protection circuitry.

Redundant circuitry was available, I

I therefore the health and safety of the general public was not endangered.

This event I o c is reportable as per T.S. 6.9.1.9.a.

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NAME OF PREPAREH PHONE:

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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.