ML20091A189

AO 263/74-13:on 740527,B Loop Torus Cooling Injection Valve Would Not Close Using Control Room Handswitch.Wire from Thermal Overload Relay Interfered W/Opening Contactor Auxiliary Contact Assembly.Wire Rerouted

ML20091A189
Person / Time
Site:	Monticello
Issue date:	06/04/1974
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
AO-263-74-13, NUDOCS 9105140435
Download: ML20091A189 (2)

Text

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Regulatory Docket File NSD NORTHERN STATES POWER COMPANY Minneapolis, Minnesota 55401

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Mr. J. F. O' Leary, Director Directorate of Licensing Nfe > # s W -

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Office of Regulation United States Atomic Energy CommissiSr'J ' '

Washington, D. C. 20545 ._. .

Dear Mr. O' Leary:

>D.NTICELLO NUCLE.\R GENERATING PLANT Docket No. 50-2i3 License No. DPR-22 A0 '63/74-13 Failure of Torus Cooling Injection Valve 50 2009 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 Provisiorial Operating License DPR-22.

On bhy 27, 1974, during routine RHR system surveillance testing, the B loop torus cooling injection valve, FD 2009, could not be closed using the control room handswitch. %e operator actuated the thermal overload reset button and then successfully closed the valve.

Investigation revealed that a wire from one of the thermal overload relays was interfering with the operation of the opening contactor auxiliary contact assembly such that the contacts occasionally remained actuated even though the contrtor was de-energized. This condition prevented the closing contactor from energizing due to the electrical interlock arrangement between the opening and closing contactors. (The interlock is intended to prevent both contactors from being energi:cd at the same time.) Subsequent testing demonstrated that the auxiliary contacts would return to the de-energized position when the over-load reset button was actuated since only a slight movement of the overload relay assembly was necessary to clear the interference.

The overicad relay wire was rerouted away from the auxiliary contact assed ly and the valve was successfully tested. To prevent a recurrence, the electrical maintenance procedures for motor operated valves will be revised to include verification of free auxiliary contact operation.

9105140435 740604 PDR ADDCK 05000263 f, S PDR

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This occurrence did not affect safe operation since FD 2LO7, a redundant ided chut-off valve located upstream of 50 200s, was operable and prov automatic isolation cap,oility.

No previous failurm d .nis natu13 have occurred on this or sit Jar valves.

It is believed that eni. was an isolated occurrence and that the planned '

additions to the maun. 'r..e ;.rocedures will ensure reliable future operation. -

Very truly yours, I 5  %

L. O. Mayer, PE Director of Nuclear Support Services LOM/rma cc: J G Keppler G Charnoff Minnesota Pollution Control Agency Attn: E A Pry::ina e

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