05000298/LER-1980-044, Forwards LER 80-044/01T-0

Forwards LER 80-044/01T-0

ML20002B937
Person / Time
Site:	Cooper
Issue date:	11/25/1980
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20002B938	List: 05000298/LER-1980-044, Forwards LER 80-044/01T-0 05000298/LER-1980-044-01, /01T-0:on 801115,reactor Scram Occurred & Normal Cooldown Rate Exceeded.Caused by Failed Card (Westinghouse- Hagan 398522) in Computer Controlled Turbine Control Sys Forcing Main Steam Bypass Valves to Remain Open
References
CNSS800686, NUDOCS 8101070355
Download: ML20002B937 (2)

LER-1980-044, Forwards LER 80-044/01T-0

Event date:
Report date:
2981980044R00 - NRC Website

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'7 COOPER NUCLEAR STATION 8w Nebraska Public Power District

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CNSS800686 November 25, 1980

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Mr. K. V. Seyfrit, Director

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U.S. Nuclear Regulatory Commission Office of Inspection and Enforcament N

Region IV 611 Ryan Plaza Drive Suite 1000 Arlington, Texas 76011

Dear Sir:

This report is submitted in accordance with Section 6.7.2.A.2 of the Technical Specifications for Cooper Nuclear Station and discusses a reportable occurrence that was discovered on November 15, 1960. This event was discussed with Mr. R. Spangler on November 15, 1980 and im-mediate notification was hand carried by Mr. Spangler to your office. A licensee event report form is also enclosed.

Report No.:

50-298-80-44 Report Date:

November 25, 1980 Occurrence Date: November 15, 1980 Facility:

Cocper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which resulted in operation of the plant such that the limiting condition for operation specified in the Technical Spec-ification 3.6.A.1 was exceeded.

Conditions Prior to Occurrence:

Reactor power was at approximately 93% of rated thermal power.

Description of Occurrence:

During performance of Surveillance Procedure 6.1.29, APRM Func-tional Test, a reactor scram occurred. Following the reactor scram, the reactor coolant temperature change exceeded the normal cooldown rate of 100 F/ hour.

' 45,,,1 8101070355 s

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. Mr. K. V. Seyfrit November 25, 1980 Page 2.

1 Designation of Apparent Cause of Occurrence:

The apparent cause of the occurrence has been attributed to a failed counter ca'd in the Digital Electrohydraulic Control System c

for the main turbine. The failed card caused the main steam bypass valves to remain open following the scram. The 825 psig reactor l

pressure closure of the main steam isolation valves did not occur because the " mode" switch was manually taken out of "Run" shortly after the scram.

Analysis of Occurrence:

The main steam bypass valves control reactor pressure during start-up and af ter a reactor scram when the main steam isolation valves l

are open.

During this event, the reactor depressurized from approximately 1000 psig to approximately 210 psig in nine minutes. This caused the reactor vessel metal temperature to decrease approximately 150 F during the next hour. This temperature transient is similar to the " stuck open relief valve" transient and is not limiting in the reactor vessel thermal cycles analysis at this time.

Subse-quent reactor vessel operation at pressure is permitted without any special limitation due to this_ transient. This event presented no j

adverse consequences from the standpoint of public health and safety.

Corrective Action

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The failed component was replaced and tested during the outage subsequent to this occurrence. A review of operator actions during surveillance tests of this type and actions following scrams are being reviewed. This review will be completed by February 28, 1981.

i Sincerely, i

L. C. Lessor Station Superintendent l

Cooper Nuclear Station LCL:cg l

Attach.

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