ML20058K609

Ro:On 740410,broken Stem on RHR Svc Water Control Valve, CV-1728,discovered During Insp.Control Valve in Redundant Sys Will Be Inspected During Current Outage

ML20058K609
Person / Time
Site:	Monticello
Issue date:	04/18/1974
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9102120635
Download: ML20058K609 (2)

Text

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~ kW8t00' Docket File ggy NORTHERN STATES POWER COMPANY .i M 8 N N E A PO LI S. M I N N E S OTA 55401 op

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April 18, 1974

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Mr. J F O' Leary, Director W , g . . . . ,

Directorate of Licensing pkarc ),~ r 4Pgg O/g g

Office of Regulation . y W U S Atomic Energy Commission '

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Dear Mr. O' Leary:

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MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Broken Stem on RHR Service Water Control Valve, CV-1728 A condition occurred at the Monticello Nuclear Generating Plant which we are reporting to your office in accordance with Section 6.7.B.1, Abnormal Occurrence Reports, of Appendix A, Technical Specifications, of Provisional Operating License DPR-22.

On April 10, 1974, an inspection of the RHR Service Water Control Valve, CV-1728, revealed that the lower valve stem was broken. Further inspection revealed significant metal erosion below the lower port disc. (See attached figure) The nature of these failures and the design of the valve are such that the valve was still able to perform its functiot. of controlling differ-ential pressure between the RER and RHR Service Water. The valve operator withdraws the stem to a given position and maintains that position through a position feedback device. The inner valve is designed to open when either normal flow or normal dif ferential pressure forces are appled across the valve ports. Consequently, the inner valve will be forced open by hydraulic forces until it is restrained at the required position by the severed lower stem.

This is the first failure of this type which has been experienced. Metallurgical and raechanical investigations to determine the cause of the stem fracture and the erosion are continuing. The control valve in the redundant system will be inspected during the current outage. Following the corepletion of the metallurgical and mechanical tests and the inspection of the redundant system, a report on the final resolution of the problem will be submitted.

Yours very truly, 9102120635 74041863 j, CF ADOCK 050 L 0 Mayer, PE Director of Nuclear Support Services LOM/kn o; --

yO10 cc: J G Keppler G Charnoff ., - , .

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