ML20010A136

Forwards LER 81-018/03L-0.Detailed Event Analysis Encl

ML20010A136
Person / Time
Site:	Cooper
Issue date:	07/22/1981
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20010A137	List: ML20010A136 ML20010A139
References
CNSS810427, NUDOCS 8108110104
Download: ML20010A136 (2)

Text

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COOPER NUCLEAR ST ATioN

- - -Nebraska Public

- - _ - - -Power

- _ . _ . -District

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CNSS810427 July 22, 1981 j-

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Mr. K. V. Seyfrit, Director U.S. Nuclear Regulatory Commission s{-

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M Office of Inspection and Enforcement /J Region IV 611 Ryan Plaza Drive Suite 1000 Arlington, Texas 76011

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 occ'irrence that was discovered on June 25, 1981. A licensee event report form is also enclosed.

Report No.: 50-298-81-18 Report Date: July 22, 1981 Occurrence Date: June 25, 1981 Facility: Cooper Nuclear Station Brownville, Nebraska 68321 _

Identification of Occurrence:

Operation with an engineered safety feature instrument setting less conservative than those established in Table 3.2.B, page 1 of the Technical Specifications.

Conditions Prior to Occurrence:

The reactor was operating at a steady state power level of approx-imately 98% of rated thermal power.

Description of Occurrence:

While performing Surveillance Test Procedure 6.2.2.1.3, pressure switch NBI-PS-52A was found to trip at s. setpoint higher than that allowed by Technical Specifications.

Designation of Apparent Cause of Occurrence: S The apparent cause of this occurrence was setpoint drift.

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8108110104 810722 32.-

DR ADOCK 05000 g

Mr. K. V. Seyfrit July 22, 1981 Page 2.

Analysis of Occurrence:

The function of pressure switch NBI-PS-52A is to monitor reactor pressure and to initiate Core Spray.and Residual Heat Removal Valve open permissive circuitry at jL450 psig. The switch setpoint was found to trip at 452 psig. The redundant pressure switches, NBI-PIS-52B, PS-52C, and PIS-52D, were also tested at the time of the occurrence and operated properly within Technical Specification limits.

The switch was examined and no apparent cause for the setpoint drift con 1d be found. Surveillance Procedure 6.2.2.1.3, which discovered NBI-PS-52A in violation of Technical Specifications, was performed at the end of a scheduled refueling outage. A review of the previous calibration records revealed'that this switch had demonstrated a drift in the upward direction after several re-fueling outages, but not enough to violate the Technical Spec-ification setpoint. There was.no appreciable drifting of the instrument between outages. This occurrence presented no adverse consequences from the standpoint of public health and safety.

Corrective Action:

Pressure switch NBI-PS-52A was readjusted to the correct setpoint at the time of occurrence. Investigation of the setpoint for NBI-PS-52A indicated that the shut off head of the Core Spray and Re-sidual Heat Removal pumps was approximately 350 psig. The Teeb-nical Specification setpoint of j[450 psig for NBI-PS-52A prevents over-pressurization of the CS and RHR piping and reduces the dif-ferential pressure across the valves during the opening sequence.

The setpoints for pressure switches'NBI-PS-52A and redundant pres-sure switches NBI PIG-52B, PS-52C, and PIS-52D were subsequently reset to 400 psig in order to provide a greater margin from the Technical Specification limit and still ensure that the valve opens before the shut off head of the'ECCS pumps is reached in the accident sequence.

Sincerely,

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L. C. Lessor i Station Superintendent

Cooper Nuclear Station LCL:cg Attach.

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