ML19256G558

Forwards LER 79-035/03L-0

ML19256G558
Person / Time
Site:	Cooper
Issue date:	12/07/1979
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19256G559	List: ML19256G558 ML19256G568
References
CNSS-790639, NUDOCS 7912310459
Download: ML19256G558 (2)

Text

4 COOPER NUCLEAR STATloN P.o. Box 98, BRoWNVILLE, NE8RASKA 68321 Nebraska Publ.ic Power D.

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ic t TEtEmo~E emi ns.38n CNSS790639 December 7, 1979 Mr. K. V. Seyfrit.

U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement 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 occurrence that was discovered on November 9, 1979. A li-censee event report form is also enclosed.

Report No.: 50-298-79-35 Report Date: December 7, 1979 Occurrence Date: November 9, 1979 Facility: Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which may have led to operation in a degraded mode permitted by the limiting condition for operation in Section

3. 5. A.l. (2) of the Technical Specifications.

Conditions Prior to Occurrence:

The reactor was at a steady state power of approximately 96% of rated thermal power.

Description of Occurrence:

During routine surveillance testing, a Core Spray (CS) valve (CS-M0-12A) failed to open by remote switch.

Designation of Apparent Cause of Occurrence:

The apparent cause of this occurrence has been attributed to axial movement of the worm set clutch collar thus damaging the clutch fingers and disallowing the full engagement reouired for electrical operation of the valve. g/'

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Mr. K. V. Seyfrit December 7, 1979 Page 2.

Analysis of Occurrence:

The CS Systems (A & B) are low pressure emergency core cooling systems. Each CS injection line has two valves, one normally closed (CS-MO-12) and one normally open (CS-MO-ll) . Both valves receive "open" signals during a CS system initiation. The CS-MO-12A valve operator is a Limitorque type SMB-2, with an AC motor operator.

During disassembly of the Limitorque operator, metal particles and a nylon pin were found in the grease. The clutch fingers on the worm set clutch gear, worm set clutch, and handwheel clutch pinion were damaged. The four retaining setscrews in the worm set clutch collar were missing and this allowed axial movement. The loose nylon pin found in the grease verifies that the worm set clutch collar had significant axial movement.

At the time of the occurrence, the redundant valve, CS-M0-11A, was closed. CS-MO-12A was opened by harlwheel operation and tagged open. The "A" loop of the CS systev remained available and op-erable. The "B" loop of CS and the redundant system, Low Pressure Coolant Injection, were operable during this event.

This occurrence presented no adverse consequences to the public health and safety.

Corrective Action:

The damaged parts were replaced with identical replacements and the setscrews in the worm set clutch collar were verified in place and staked.

A review of the equipment history indicated that this valve op-erator had not been disassembled by station personnel. Maintenance has been performed on numerous identical valve operators and in only one other instance have the four subject setscrews been missing (Reference LER 79-07). Future maintenance on the subject valve operators will insure proper installation of the setscrews.

Sincerely, C

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C P h.~

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

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