ML19345G161
| ML19345G161 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 06/03/1974 |
| From: | Hartley F CONNECTICUT YANKEE ATOMIC POWER CO. |
| To: | |
| References | |
| AO-50-213-74-9, NUDOCS 8103090066 | |
| Download: ML19345G161 (2) | |
Text
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ABil0RMAL OCCURRENCE REPORT o:-
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Report E June 3, 1974
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7 nce Date:
May 23, 1974 Facility:
Connecticut Yankee Atomic Power Company Identification of Occurrence:
Protective Instrumentation Setpoint Drift Conditions Prior to Occurrence:
Steady State Power; conducting routine bi-monthly nuclear instrumentation over-power trip setpoint check.
Description of Occurrence:
During a routine bi-monthly nuclear overpower trip setpoint check, two of four nuclear overpower trip setpoints were found 1% over the required 109%. The setpoints were adjusted to $107.5%.
Designation of Apparent Cause of Occurrence:
Normal instrumentation drift; trip setpoints too close to Technical Specifications limit.
Analysis of Occurrence:
Reactor neutron flux at power is measured by four separate channels. '
If the power level reaches 109% of full power on any of two of the four channels a reactor trip will be initiated. The setpoint of 109% includes an allowance for drift and setpoint error, calorimetric error and flux deviation due to rod motion. The maximum overpower correction prior to reactor trip that could result from the worst possible combination of l
these errors is 118% of rated power. The reactivity accidents analyzed l
in the Facilities Description and Safety Analysis are based upon an over-power reactor trip at the 118% setting.
We therefore conclude that the 1% drift in setpoint to 110% on two channels was within the normal expected instrumentation drift range, as described in the FDSA.
It is not expected that this situation will reoccur with the overpower trip setpoints re-adjusted to allow for normal instrumentation drift.
Corrective Action:
The setpoints on the two channels were adjusted to s107.5% to allow for normal instrument drift without exceeding the specified limit of 109%.
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ABfl0Rl1AL OCCURREfCE REPORT'(Continued) l 1
Failure ata:
The nuclear overpower trip setpoint data over '.he'past four years was reviewed and the instrumentation setpoint drift averaged s0.5%.
This is well within the expected range of 2%.
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(:lI at
-t_j a-t t v u, Plant Superintghdent l
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