05000298/LER-1981-003, Forwards LER 81-003/03L-0.Detailed Event Analysis Encl

Forwards LER 81-003/03L-0.Detailed Event Analysis Encl

ML20008F703
Person / Time
Site:	Cooper
Issue date:	03/25/1981
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20008F704	List: 05000298/LER-1981-003, Forwards LER 81-003/03L-0.Detailed Event Analysis Encl 05000298/LER-1981-003-03, /03L-0:on 810223,RHR-MO-26B Motor Amps Increased & Remained Excessively High When Valve Reached Closed Position.Caused by Limit Switch on Limitorque SMB-O Valve Motor Operator Not Opening & de-energizing Starter
References
CNSS810164, NUDOCS 8104210519
Download: ML20008F703 (3)

LER-1981-003, Forwards LER 81-003/03L-0.Detailed Event Analysis Encl

Event date:
Report date:
2981981003R00 - NRC Website

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d Mr. K. V. Seyfrit, Director

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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 February 23, 1981. A licensee event report form is also enclosed.

Report No.:

50-298-81-03 Report Date:

March 25, 1981 Occurrence Date: February 23, 1981 Facility:

Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which lead to operation in a degraded mode permitted by a limiting condition for operation established in Section 3.5.B.3 of the Technical Specifications.

t Conditions Prior to Occurrence:

The reactor was at a steady state power level of approximately 98%

l of rated thermal power.

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l Description of Occurrence:

l During perfor=ance of Surveillance Procedure 6.3.5.2, valve RHR-MO-26B motor current increased and remained high when the valve reached the closed position. The valve motor breaker was manually tripped and the valve was declared inoperable.

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Mr. K. V. Seyfrit March 25, 1981 Page 2.

Designation of Apparent Cause of Occurrence:

It is believed that the limit switch inside the valve motor oper-ator did not open when the valve reached its closed position.

Therefore, the closing torque switch could not open and the starter could not deenergize. Had it not been tripped manually, the motor would have overheated and failed in the closed position.

Analysis of Occurrence:

RHR-MO-26B is the outboard isolation valve in the drywell spray line. This is a normally closed valve that receives a closure signal on ECCS initiation. The inboard isolation valve was oper-ational as well as both isolation valves in the redundant RHR loop.

The core spray system and both diesels were operable. This valve is required to be open only for drywell spray. Drywell spray can be performed during an ECCS initiation with reactor water level above 2/3 core height and 2 psig in the drywell. In the event this valve needed to open, it would have opened without receiving the overcurrent on the motor as demonstrated during previous steps of the subject surveillance procedure. This valve was inoperative for about 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. It did not maka RHR pumps inoperable, nor would it have prevented the system from performing its function of low pressure coolant injection.

A similar problem occurred on November 3,1980, however, the symptoms of this problem did not directly relate to an improperly adjusted limit switch. Based on the analysis of this occurrence, it is apparent that the November 3, 1980 occurrence was initiated by the subject limit switch.

At this point in time, the facts indicate that the subject limit switch is somewhat non-repetitive with respect to indicating a closed valve position. The valve position indicated by the limit switch is the actual valve stem position. An internal mechanical interference could prevent the valve from positioning itself in the exact location each time the valve is closed. This mechanical interference would not make the valve inoperable. However, it would cause the limit switch to become non-repetitive.

This occurrence presented no adverse consequences from the stand-point of public health and safety.

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Mr. K. V. Seyfrit March 25, 1981 Page 3.

Corrective Action

The valve operator was carefully inspected and the closed limit switch adjusted. The valve was cycled several times and correct operation verified.

Subsequent operation of this valve was sat-isfactory. RHR-M0-26B is scheduled for disassembly and inspection during the April 1981 refueling outage.

- A copy of this LER is being routed to the involved personnel stressing the importance of insuring limit and torque switches are adjusted properly and re-spective logic systems checked accordingly during any maintenance activity on motor operated valves.

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

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