ML19257D830

Significant Deficiency Rept SD-369/370-79-14:on 790116, During Prototype Testing,Isolation Block Valve Failed to Fully Close Under Design Flow Conditions.Caused by Manufacturer Error in Determing Size of Valve Operator

ML19257D830
Person / Time
Site:	McGuire, Mcguire
Issue date:	01/16/1980
From:	DUKE POWER CO.
To:
Shared Package
ML19257D822	List: ML19257D821 ML19257D830
References
SD369-370-79-14, NUDOCS 8002060562
Download: ML19257D830 (1)

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Report No.- SD-369-370/79-14 Report Date: January 16, 1980 Facility: McGuire Nuclear Station, Units 1 and 2 Identification of Deficiency: Pressurizer PORV Block Valves s

Description of Deficiency:

Duke Power Company has implemented prototype testing of a pressurizer power operated relief valve (PORV) and an isolation block valve for both McGuire Nuclear Station and Catawba Nuclear Station. During this testing, conducted at the Marshall Steam Station, the isolation block valve failed to fully close imder design flow conditions. The isolation valve is manufactured by the Nuclear Valve Division of Borg Warner and uses a Rotork electric motor operator.

The valve manufacturer made a calculational error in determining the proper size of the valve operator. Excessive frictional forces, developed during valve closure at full flow conditions, were not properly considered.

Analysis of Safety Implications:

Coupled with a single failure of the pressuerzer power operated relief valve, failure of the isolation block valve to fully close would result in depressuri-zation of the Reactor Coolant System and subsequent overfilling of the pressurizer relief tank.

Corrective Action:

Continued testing by Duke has resulted in several valve and operator design modifications which will be implemented by the valve nanufacturer as follows:

1) As adequately sized motor operator will replace the previous operator.

2) The valve disc gate to the stem connections will be strengthened to withstand increased " pullout" forces from the larger operator.

3) Contouring and rounding of valve disc contact areas will be performed to minimize frictional forces developed.

The above actions are currently being performed on a new valve which will then be installed and tested at tiarshall Steam Station to full flow and pressure conditions. Corrective action for McGuire valves will be completed prior to Hot Fuctional Testing. - - .

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