ML19345G158
| ML19345G158 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 06/28/1974 |
| From: | Hartley F CONNECTICUT YANKEE ATOMIC POWER CO. |
| To: | |
| References | |
| AO-50-213-74-11, NUDOCS 8103090050 | |
| Download: ML19345G158 (2) | |
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AllSREL URRENCE REPORT 4
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Report Date:
6-28-74
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Occurrence Date:
6-20-74 Facility:
Haddam Neck Plant Identification of Occurrence:
Unsatisfactory Surveillance Test - Low Pressure Trip Unit Conditions Prior to Occurrence:
Steady state power; conducting routine six week pressurizer pressure setpoint test.
Description of Occurrence:
In accordance with the surveillance requirements of Section 4.2 of the Connecticut Yankee Technical Specifications, pressurizer pressure instrument setpoints are tested every six weeks. During the pressurizer pressure surveillance test conducted June 20, 1974, one of the three low pressurizer pressure trip units operated approximately 15 psi beyond the acceptance criteria.
Designation of Apparent Cause of Occurrence:
Possible setpoint drift.
Analysis of Occurrence:
A variable low pressure trip signal is generated whenever the pressurizer pressure is lower than a calculated variable low pressure setpoint. This setpoint is continuously calculated from measurements of reactor coolant temperature and core power.
Each of the three independently calculated setpoints is continuously compared with one of the three pressurizer pressure measurements, giving three independent trip channels. Any trip signal generated from these channels is transmitted to a matrix of relay contacts which initiates a reactor trip upon coincidence of two of the three signals. Two of the three trip channels were within acceptable limits, however the third channel was 15 psig outside acceptable limits.
Upon discovery of the out of specification condition, a trip signal was inserted to satisfy the one out of two logic required for continued full power operation.
It is our opinion that this slight drift outside specified limits did not present a hazard to the health and safety of the public.
Corrective Action:
The faulty trip unit was replaced and is presently under-going bench tests in an attempt to determine the cause of the incorrect trip setpoint. The
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ABNORMAL OCCURRENCE REPORT 50-213/74-11 6-28-74 l
new unit was tested and subsequently returned to service. The trip setpoint was adjusted to allow for normal instrumentation drift.
Failure Data:
The trip / alarm unit is a Foxboro Model 635. There is no record of previous problems with this equipment.
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