ML20127L829

Ro:On 730810,during Routine Plant Startup,Outboard Main Steam Line Drain Valve MO-2374 Could Not Be Closed Using Control Room Handswitch.Caused by Misajusted Closing Contactor.Interlock Properly Adjusted

ML20127L829
Person / Time
Site:	Monticello
Issue date:	08/17/1973
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9211250285
Download: ML20127L829 (2)

Text

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e. Regulatory DocH File HSD POWER COMPANY

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NORTHERH STATES Minneapolis, Minnesota 55401

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s e h August 17, 1973 d Doc m to a # k .Q[Q

. AUG2 973 J &

Mr. J. F. O' Leary, Director s .

c Directorate of Licensing United States Atomic Energy Canaission 0 u$f7IO"Y 00crpl[$ g k;(b.h@y@N

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'k ,QA Washington, D. C. 20545  % \/bf co

Dear Mr. O' Leary:

hDNTICELLO NUCLEAR GENTRATING PUAT Docket No. 50-263 License No. DPR-22 N Failure of Main Steam Line Drain Valve, MO-2374, to Close -

A condition occurred at the Monticello Nuclear Generating Flant which we are reporting to your office in accordance with Section 6.7.B.1, Abnormal Occurence Reports, of the Technical Specifications, of Provisional Operating License DPR-22.

On August 10, 1973, during a routine plant startup, the outboard main steam line drain valve, M0-2374, a primary containment isolation valve, could not be closed using the control roon handswitch.

Investigation revealed that the valve mctor closing contactor was properly energized but that its main contact was not closed. It was determined that the mechanical interlock with the corresponding opening contactor was prevent-ing the closing contactor main contact from properly closing. The interlock is constructed such that it b?ocks the opening contactor amature when the closing contactor is picked up, or conversely, blocks the closing contactor armature when the opening contactor is picked up. The interlock was adjusted to allow proper operation of the closing contactor The valve was then success-fully operated.

Similar contactors for the other DC motor-operated valves were inspected to verify proper adjustment of the mechanical interlocks. One other contactor interlock was found out of adjustment although it was functioning properly. -

The remainder of the contactors inspected were found to be satisfactory. The outboard head spray isolation valve contactors were not inspected since this valve is held closed by a reactor pressure interlock and cannot be cycled during nonnal power operation. The contactors for this valve will be inspected at the first opportunity. Adjustment of the contactor interlocks will be incorporated into the breaker maintenance procedure.

This occurrence did not affect safe operation since the redundant inboard main steam line drain valve was fully operabic.

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92112502B5 730817 (;387 l PDR- ADOCK 05000263 l S PDR

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One previous malfunction has occurred due-to improper assembly of 'a mechanical interlock, however, no previous malfunctions due to improper adjuatment have been experienced. --It is felt that the corrective actions taken as a result of this occurrence are sufficient- to insure reliable operation of the DC motor operated valves.

.Yours very truly, L 0 Mayer, PE n1ut m e Director of Nuclear Support Services ID4/nnn cc: B li Grier G Charnoff blinnesota Pollution Control Agency Attn: Ken Dnigan

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