ML20127L295

Ro:On 730801,MSIV 2-80A Closed in 6 Seconds in Excess of Allowable TS of 3-5 Second Closure.Caused by Frictional Resistance Between Spring Support Yoke & Yoke Rods.C/A Included Readjusting Rollers & Lubricating Contact Areas

ML20127L295
Person / Time
Site:	Monticello
Issue date:	08/10/1973
From:	NORTHERN STATES POWER CO.
To:	US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9211230485
Download: ML20127L295 (1)

Text

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NORTHERN STATES POWER COMPANY MINN E A POLIS. MIN N E SOTA 88401 V

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Mr. J P 0'1cary, Director 6 b4 -

• Directorate of Licensing k(6' D $ 6p^ Q

<fhv United States Washington, D CAtomic 20545 Energy Cocanissio hg j (#Of, h q,h We,s;, %-

Dear Mr. O' Leary:

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MONTICELLO NUCLEAR GENERATING PLANT Doci.c t No. 50-263 License No. DPR-22 Slow Closure of a Main Steam Isolation Valve 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 ting License DPR-22 Reports, of the Technical Specifications, of Provisional Opera -

On in 6 August seconds.1,1973, during routine surveillance testing, MSIV 2-80A closed fication of 3-5 seconds closure.This closure was in excess of the allowable Technical was being slowed the last 107, of stroke due to frictional resistanceAn inv between the spring support yoke and the yoke rods.

pair of yoke rods, rollers attached to the top of the yoke were not riding on theIt was noted that th last portion of the valve closure stroke.thus allowing metal to metal contact p Corrective maintenance included rods, burnishing the galled areas on the yoke rods, and lu contact areas between the rollers and yoke rods.

During subsequent timing tests the valve operated smoothly and without interference, closing in lesshowever, after several exercises the valve was noted t o be than 3 seconds.

' low and the flow restrictor assembly air bound.The dashpot oil level was found to be The dashpot was filled and closure.vented, allowing The inboard the MSIV to be satisfactorily tested at 4 seconds "A" MSIV oil dashpot is particularly difficult to fill and vent since the valve is canted from the vertical plane in such i

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