ML19347C784
| ML19347C784 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 05/29/1975 |
| From: | CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| References | |
| AO-11-75, NUDOCS 8102170118 | |
| Download: ML19347C784 (1) | |
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ABNORMAL OCCURRENCE REPORT Big Rock Point Plant 1.
Report No: A0-11-75, Docket 50-155 2a.
Report Date: May 29, 1975 2b.
Occurrence Date: May 20, 1975 3.
Facility: Big Rock Point Plant, Charlevoix h.
Identification of Occurrene_e_: Pressure Switch Drift on Condenser Lov Vacuum Scram Interlock 5
Condition Prior to Occurrence: Plant in cold shutdown for modification activities associate with A0-1-75 6.
Description of Occurrence: During routine calibration of vacuum inter-lock switch PS/RE15B, the set point was found to be 362 psig. The Technical Specifications call for less than 350 psig - Ref 6.13(E) footnote in Technical Specifications. The switch has been readjusted to operate at 339 psig.
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Designation of Apparent Cause of Occurrence: Pressure switch drift -
both increase and decrease have been experienced in the past with these switches. The basic problem is a misapplication in that a wide range switch has been used with a set point at the extreme low end.
Also, the switch cannot be set much below 350 psig because of the restrictive reset characteristic of the vacuum scram switch which resets at approxi-mately 25" Hg.
This is difficult to achieve at reactor pressure below approximately 3ho psig.
8.
Analysis of Occurrence: The operating point of 12 psig above the limit occurred on one of two switches in the protective system channel and, thus, the protective function was operable. The proposed Technical Specifications of March 11, 1975 indicate our request to raise this limit to 500 psig based on settings that are allowed in another sirtilar BWR plant. As the purpose of the switch is to insure that the n,rmal heat sink is available during reactor operation at significant power levels, the drifting of the set point of this switch as experienced has no effect on the safety of operation of the plant. Operation at signifi-cant power levels does not occur below a pressure of approximately 1,000 psia.
9 Corrective Action: The switch was reset to operate at 339 psig on May 20, 1975 10.
Failure Data:
Reference similar problem with PS/RE15B in A0-7-73 reported
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in our letter of May 8,1973 and A0-12-73 reported in our letter of November 13, 1973, component manufacturer, Barksdale Model B1T/i32SS.
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