ML19257C593

Forwards LER 79-039/03L-0

ML19257C593
Person / Time
Site:	Cooper
Issue date:	12/28/1979
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19257C594	List: ML19257C593 ML19257C621
References
CNSS790696, NUDOCS 8001290460
Download: ML19257C593 (2)

Text

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COOPER NULLEAR ST ATioN

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Nebraska Public Power District "'A*E" *"OA";

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CNSS790696 December 28, 19)'i Mr. K. V. Seyfrit U.S. Nuclear Regulatory Cot: mission Office of Inspection and Enforcecent Region IV 611 Ryan Plaza Suite 1000 Arlington, Texas 76011

Dear Sir:

This report is submitted in accordance with Section 6.7.2.B.2 of the Technical Specifications for Cooper Nuclear Station and discusses a reportable occuirence that was discovered on November 29, 1979. A licensee event report form is also enclosed.

Report No.. 50-298-79-39 Report Date: December 28, 1979 Occurrence Date: November 29, 1979 Facility: Cooper Nuclear Station Brownville, Nebraska 68321 Identif' _ tion of Occurrence:

A condition which resulted in operation in a degraded mode per-mitted by a limiting condition for operation established in Section 3.7.D.2.

Conditions Prior to Occurrence:

The reactor was at steady state power level of approximately 87% of rated thermal power.

Description of Occurrence:

The suppression chamber inboard vent isolation valve (PC-2 30FN) would not operate "* *... De control switch and there was no position indication in the control room.

1827 006

/90o3 3

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eco noo $6 0 ,

Mr. K. V. Seyfrit December 28, 1979 Page 2.

Designation of Apparent Cause of Occurrence:

Examination of the geared limit switch on the motor operator for the subject valve revealed that rotor controlling the position indication and opening control circuit had cracked. The rotor was lodged in its limit switch assembly.

Analysis of Occurrence:

PC-230MV is the suppression chamber inboard vent isolation valve.

PC-230MV failed in the closed position which is its normal oper-ating position. It is one of two butterfly valves in this vent-11ation line which receives a closure signal by a Group 2 isolation signal . The other valve in line (PC-245AV) was operable and would have provided isolation if required. Since it also is normally closed, this occurrence presented no adverse consequences from the standpoint of public health and safety.

The limit switch assembly of the Limitorque SMB00 operator was carefully inspected. No particular reason for the failure could be determined. The rotor was broken near one set of contacts. This type of failure has not been experienced at Cooper Nuclear Station.

Discussion with the vendor indicates that this rotor may break if it is subjected to high vibration or shock. This valve is not subjected to hign vibration or shock.

Corrective Action:

PC-245AV was tagged in the closed position. The Limitorque op-erator was inspected and repaired with a qualified replacement part. All assemblies in the operator were inspected for alignment and proper tightness. The Limitorque operators will be closely conftored for further problems. This event was discussed with the appropriate maintenance personnel.

Sincerely,

.k -

L. C. Lessor Station Superintendent Cooper Nuclear Station LCL:cg Attach.

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