05000338/LER-1980-052-03, /03L-0:on 800530,preliminary Analysis Results of Turbine First Stage Pressure Input to Interlock P-7 Indicated That Setpoints Exceeded Tech Spec Limits.Cause Undetermined.Changes to Calibr Procedures Will Be Made

/03L-0:on 800530,preliminary Analysis Results of Turbine First Stage Pressure Input to Interlock P-7 Indicated That Setpoints Exceeded Tech Spec Limits.Cause Undetermined.Changes to Calibr Procedures Will Be Made

ML19326D750
Person / Time
Site:	North Anna
Issue date:	06/30/1980
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19326D747	List: 05000338/LER-1980-052, Forwards LER 80-052/03L-0 05000338/LER-1980-052-03, /03L-0:on 800530,preliminary Analysis Results of Turbine First Stage Pressure Input to Interlock P-7 Indicated That Setpoints Exceeded Tech Spec Limits.Cause Undetermined.Changes to Calibr Procedures Will Be Made
References
LER-80-052-03L, LER-80-52-3L, NUDOCS 8007030269
Download: ML19326D750 (2)

LER-1980-052, /03L-0:on 800530,preliminary Analysis Results of Turbine First Stage Pressure Input to Interlock P-7 Indicated That Setpoints Exceeded Tech Spec Limits.Cause Undetermined.Changes to Calibr Procedures Will Be Made

Event date:
Report date:
3381980052R03 - NRC Website

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U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT CCNTROL BLOCK / / / / / / / (1)

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On May 30, 1980 preliminary analysis results of turbine first stage pressure

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inputs to interlock P-7 (blocks at power reactor trips below 10% RATED THERMAL /

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POWER) indicated the setpoint specified in a calibration procedure exceeded

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the T.S.

limit by 0.26% RATED THERMAL POWER.

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Since the NI power range input to P-7 is properly cali-

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The cause of the improper setpoints has not been detern:ined.

A setpoint

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change study is being conducted, changes to the calibration procedures will

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be made, and the P-7 setpoints will be changed.

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Virginic Electric cnd Pow:r Ccmptny North Anna Power Station, Unit 1

Attachment:

Page 1 of 1 Docket No. 50-338 Report No. LER 80-052/03L-0

Description of Event

Reactor trip system interlock P-7 is used to bypass the high pressurizer level and low pressurizer pressure reactor trips during low power or startup operation.

It is also used to bypass reactor coolant low flow, reactor coolant pump breakers open in more than one loop, andervoltage (RCP busses), underfrequency (RCP busses), and turbine trip signals to the Reactor Protection System.

It is derived from bistable circuits indicating less than 10% RATED THERMAL POWER (power level increasing) or 8% RATED THERMAL POWER (power level decreasing) as measured by both the first stage turbine pressure and the power range nuclear instrumentation channels.

P-7 is deactivated at 10% RATED THERMAL POWER (power level increasing) by 2 of 4 power range inputs (P-10) or 1 of 2 first stage turbine pressure inputs (P-13).

P-7 is activated at 8% RATED THERMAL POWER (power level decreasing) by 3 of 4 power range inputs (P-10) and 2 of 2 turbine first stage pressure inputs (P-13).

On May 30, 1980 Vepco North Anna Power Station instrument personnel conducted a preliminary study of the setpoints for interlock P-7 after a review of the results of an engineering study relating first stage

- turbine pressure to reactor power. The results of this preliminary study indicated the setpoints specified for the P-13 inputs to P-7 in a calibration procedure exceeded the T.S. limit by 0.26% RATED THERMAL POWER. Ongoing investigation by the Safety Engineering Staff indicates that the setpoints could be in error by as much as 6% RATED THERMAL POWER.

This event is reportable pursuant to T.S. 6.9.1.9.a.

This event effects P-7 setpoints on both Units 1 and 2.

Probable Consequences of Occurrance The P-10 (power range) inputs to P-7 are properly calibrated and will deactivate P-7 at the specified setpoints; therefore, the public health and safety are not effected.

Cause of Event

- The cause of the improper setpoints has not been determined.

Immediate Correct Action A setpoint study to determine if the setpoints were in error was initiated after assumptions made in the preliminary study were found to be incorrect.

Setpoint study results indicate that the setpoints could be in error by as much as 6% RATED THERMAL POWER.

l Scheduled Corrective Actions A setpoint study specifying new setpoints is in progress.

The setpoints for the P-13 inputs to P-7 will be recalibrated basec en the results of the setpoint study.

Actions Taken to Prevent Recurrance No actions to prevent recurrance are required.