05000298/LER-1982-024, Forwards LER 82-024/03L-0.Detailed Event Analysis Submitted

Forwards LER 82-024/03L-0.Detailed Event Analysis Submitted

ML20028F076
Person / Time
Site:	Cooper
Issue date:	01/20/1983
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Jay Collins NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20028F077	List: 05000298/LER-1982-024, Forwards LER 82-024/03L-0.Detailed Event Analysis Submitted 05000298/LER-1982-024-03, /03L-0:on 821221,pressure Switch RHR-PS-120A Setpoint Found Outside Range Specified in Tech Specs.Caused by Failed Diaphragm.Pressure Switch Adjusted & Subsequent Testing Showed Nonrepeatable Trip Point.Switch Replaced
References
CNSS830039, NUDOCS 8301310122
Download: ML20028F076 (2)

LER-1982-024, Forwards LER 82-024/03L-0.Detailed Event Analysis Submitted

Event date:
Report date:
2981982024R00 - NRC Website

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COOPER NUCLEAR $T ATioN Nebraska Public Power District

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JAN 2 41983 Mr. John T. Collins, Regional Administrator

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sj U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region IV 611 Ryan Plaza Drive Suite 1000 Arlington, Texas 76011 j

Dear Sir:

This report is submitted in accordance with Section 6.7.2.B.1 of the Technical Specifications for Cooper Nuclear Station and discusses a reportable occur-rence that was discovered on December 21, 1982. A licensee event report form is also enclosed.

Report No.:

50-298-82-24 Report Date:

January 20, 1983 Occurrence Date:

December 21, 1982 Facility:

Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A safety system setting discovered to be not in compliance with the requirements of Table 3.2.B of the Technical Specifications.

1 Conditions Prior to Occurrence:

The reactor was at a steady state power of 99% of rated thermal power.

Description of Occurrence:

During the performance of Surveillance Procedure 6.2.2.1.4 The setting of pressure switch RHR-PS-120A (Reactor Heat Removal (RHR) pump "A" discharge pressure) was found to be 184 psig. The required setpoint is 150 psig and the switch should trip between 100 and 165 psig per Table 3.2.B of the Technical Specifications.

Designation of Apparent Cause:

The apparent cause for the setpoint drift and subsequent setpoint in-stability was failure of the pressure switch diaphragm.

1 Analysis of Occurrence:

Pressure switch RHR-PS-120A provides a RHR pump "A" discharge pressure signal to Automatic Depressurization System (ADS) logic. This signal confirms that a RHR Low Pressure Coolant Injection (LPCI) pump is running prior to commencing ADS blowdown. A redundant discharge pressure switch v, pb 8301310122 830120 e

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Hr. John T. Collins January 20, 1983 Page 2 signal from RHR pump "A" to ADS logic is provided by RHR-PS-105A. The redundant pressure switch was operable at the time RHR-PS-120A pressure setpoint was found out of the Technical Specification limit.

The apparent cause of the setpoint drift has been traced to a defective diaphragm. A bubble was noted under the surface of the diaphragm. Two similar diaphragm failures have occurred at Cooper Nuclear Station (in 1975 and 1979) which resulted in pressure switch replacement. The previous failures were not reportable. Our analysis of these failures does not indicate that a component service life problem exists at this time. However the failure rate of this type of switch will be monitored to determine if further action should be taken in the future. This occurrence presented no adverse consequences from the standpoint of public health and safety.

Corrective Action

The pressure switch was immediately recalibrated to approximately 150 psig, but would not remain at that setting. The pressure switch was replaced and the replacement calibrated satisfactorily.

Sincerely, L. C. Lessor Station Superintendent Cooper Nuclear Station LCL:cg Enc.