ML20090E180

AO 74-5:on 740415,during Annual Refueling Shutdown Testing, Three High Temp Main Steam Line Tunnel Sensors Found to Actuate at Lower than Required Temp.Caused by Setpoint Drift on Sensor.Sensors Recalibr

ML20090E180
Person / Time
Site:	Nine Mile Point
Issue date:	04/24/1974
From:	Schneider NIAGARA MOHAWK POWER CORP.
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
References
A-74-5, A0-74-5, NUDOCS 8303140076
Download: ML20090E180 (2)

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NIAG ARA MOHAWK .PO'NER CORPORATION %0I'.,1 I D>7h y ,

MAGARA MOHAWK h[ RbCf Ybb

. 't 3 J MAY 131974 ' j- H 200 ERIE BOULEVARD WEST h[

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Mr. Donald J. Skovholt AssistaM D$ rector for Reactor Operations .

Divi'sion of' Reactor Licensing United States Atomic Energy Commission Washington, D.C. 20545

Dear Mr. Skovholt:

• In accordance with Technical Specifications 1.136 and 3.6.2 for

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Nine Mile Point Unit 1, the enclosed Abnormal Occurrence Report is'sub-mitted.r Titisreportisinaccordancewiththeformat'setforthinRegulatory Guideline 1.16.

Very truly yours, s s.

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s e. R.R. Schneider Sg s Vice President - Electric Operations

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4 ABNORMAL OCCURRENCE REPORT

1. Report No. 74-5 2a. Date April 25, 1974 2b. Occurrence Date April 15, 1974

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3. Facility Nine Mile Point Nuclear Station Unit 1 i

4. Identification of Occurrence Main Steam Line liigh Temperature Sensor Set Point Drift.

5. Conditions Prior to' Occurrence Unit I was shutdown for annual refueling.

6. Description of Occurrence During routine surveillance testing three liigh Temperature Main Steam Line Tunnel Sensors were found to actuate at a lower temperature than required. These signals provide a closure of the Mali. Steam Line Isolation Valves upon reaching 200*F. Ilowever, since the isolation function requirement is j:_200*F the necessary t, rip function would have been accomplished in the conservative direction. In as much as the set point drift was conservative no hazard would have been presented to the general public as a result of t:iis drift.

7. Designation of Apparent Cause of the Occurrence Set point Drift.

8. Analysis of Occurrence The Technical Specifications require an isolation signal be sent to the Main Steam Isolation Line Valves, in the event the tunnel temperature reaches or ex'ceeds 200*F. Ilowever, the basis for the Specification requires a deviation of + 10*F. The as found trip point of these Fenwell Temperature Detectors is as follows:

IB -10F 187*F IB-10G 186*F Ih-10P 185'F ,

9. Corrective Action The instrument was recalibrated to 200*F trip point.

10. Failure Dat;a 1st Setpoint Drift on these detectors.

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