ML19294B457

Forwards LER 80-002/03L-0

ML19294B457
Person / Time
Site:	Cooper
Issue date:	01/21/1980
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19294B458	List: ML19294B457 ML19294B459
References
CNS800058, NUDOCS 8002280429
Download: ML19294B457 (2)

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CC D PE A NUCLE AR sT AT:cN Nebraska Public Power District

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CSSS800058 January 21, 1980 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 January 3, 1980. A li-censee event report form is also enclosed.

Report No.: 50-298-80-02 Report Date: January 21, 1980 occurrence Date: January 3,1980 Facility: Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which resulted in operation in a degraded mode per-mitted by the limiting condition for operation established in Section 3.5.C.2 of the Technical Specifications.

Conditions Prior to Occurrence:

The reactor was on a flow ramp at approximately 93% of rated thermal power.

Description of Occurrence:

During an operator's tour, the HPCI stop valve stem was found broken and separar from the actuator.

Designation of Apparent Cause of Occurrence:

Failure was due to the valve stem being overstressed in this area during the process of freeing the stop valve piston when it was stuck open on September 12, 1979, (reference LER 79-25).

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Mr. K. V. Seyfrit January 21, 1980 Page 2.

Analysis of Occurrence:

The HPCI turbine stop valve is a vertically mounted inverted hy-draulically operated piston type globe valve. The function of this valve is to close quickly and stop the flow of steam to the turbine when required for turbine protection.

The valve stem and actuator are connected by a split coupling. On September 12, 1979, this coupling was found with the threads pulled out and the valve was jammed in the full open position. To free the stuck valve piston, a puller was made by putting a nut on the threaded section of the stem with washers between it and the valve body. A wrench was used on the flat section of the valve stem to keep the shaft from turning while the nut was tightened down to, pull the stem. At one point in the process, the wrench used to keep the valva stem from rotating inadvertently bottomed out in the flat. This caused the pulling force to be concentrated between the nut and this wrench, overstressing this area. At that time no damage to the shaft was noted, however, now when the shaft was compared to the replacement valve stem, the stretching of this area was apparent.

Since the valve is pushed open by the actuator and the valve piston was free to operate, the valve would have opened if required and the iiPCI System would have performed its intended safety function.

At the time of the occurrence, the redundant system, Automatic Depressurization System, as well as all low pressure emergency core cooling systeme were operable. This occurrence presented no ad-verse consequences from the standpoint of public health and safety.

Corrective Action:

The valve was disassembled and a new valve stem was installed. The valve internals were thoroughly inspected. A slight amount of deformation was noted around the top of the balance piston which was corrected. The valve was reassembled and stroked several times to check the valve operation, and the HPCI System was operationally tested by ;erformance of S.P. 6.3.3.4 before the system was re-turned to t ervice. This event was discussed with the personnel in-volved.

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