ML20084F111

Ao:On 720118,during Routine Monthly Surveillance Test, Pressurizer Pressure Bistable Failed to Deenergize on Low Pressure Set Point.Caused by Fluctuating Output of Bistable When Placed on Trip Point.Bistable Replaced

ML20084F111
Person / Time
Site:	Ginna, 05000294
Issue date:	01/27/1972
From:	Amish K ROCHESTER GAS & ELECTRIC CORP.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084F109	List: ML20084F106 ML20084F111
References
NUDOCS 8304200082
Download: ML20084F111 (2)

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S .wD ELECTi:lc CORi'3.YI?;I =- ~' ~~':"~^

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g ..s m n m t m ?co Dr. Peter A. Morris, Director ' P.

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Division of Reactor Licensing U. S. Atomic Energy Commission

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Washington, D. C. 20545

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Subject:

Detection of inoperative bistable during ',M

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1, monthly surveillance test p@ * .

R. E. Ginna Nuclear Power Plant Unit No.1 P ,Q Docket No. 50-244 , ,' '"

Dear Dr. Morris:

On January 18, 1972 during the routine monthly PT-5 Surveillance Test (Periodic Test - Process Instrumentation Reactor Trip Channels) a pressurizer pressure bistable failed to de-energize on the low pressure set point of 1715 psig.

This bistable (PC-429 D/C) has a dual acting function and did auto-matically unblock the safety injection signal from the single channel of increasing pressurizer pressure (PC-429 D). However, the simulated signal did not result in the parallel output that would permit the logic (input to safety injection from the second channel (PC-429 C) because of the bistable failure to de-energize. This failure dereated one of the three channels of redundancy provided in the low pressurizer pressure -

low pressurizer level protection channels.

In the previous monthly surveillance of December 17, 1971 this channel (PC 429 C) and the bistable (PC-429 D/C), as well as the others, per-formed normally.

The Plant Operating Review Committee met immediately and approved the use of the provisions in procedure PT-5 to replace the failed bistable with a tested replacement. This was completed, including the channel rechecking, shortly afterwards on this same date and all channels were e proven out and left in proper working order.

.2lA The removed bistable, on test, was found to have a fluctuating output

[/ when placed on a trip point. Several components within the bistable

{ were replaced ar.d the bistable functioned properly. Reinserting the

, removed components, one at a time, failed to isolate the original source

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, ec ,,Ignuary 27, $312 70 Dr. Peter A. Morris i

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of trouble. With no previous history of failure, it is now believed that that malfunction may have been caused by a random failure of a cold soldered joint.

This unit is still under test. Because of the failure to absolutely identify the reason for the malfunction, this bistable will not be reused in the reactor protection channels and will be so identified.

Very ruly yours,

.b Keith W. Amish i

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