ML20127K572

Ro:On 731028,RHR Torus Cooling Injection Valve Motor Failed Due to an Abnormal Short.Caused by Valve Open Switch Out of Adjustment.Motor Rebuilt & Limit Switches Reset.Procedures Will Be Developed to Assure Proper Adjustment for MOVs

ML20127K572
Person / Time
Site:	Monticello
Issue date:	11/07/1973
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9211200437
Download: ML20127K572 (2)

Text

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Regulatory Docket File NSP NORTHERN STATE 5 POWER COMPANY Vf' MIN N E A POU S. MIN N E t MT A 55401

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Dear Mr. O' Leary:

NA MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Failure of Torus Cooling Injection Valve, MO-2008 A condition occurred at the Monticello Nucicar 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 October 28, 1973, during performance of routine surveillance testing, the "A" Residual Heat Removal (RHR) - Torus cooling Injection Valve (M0-2008) motor failed due to an internal short.

Investigation revealed the valve open limit switch was out of adjustment such that intermediate position indication was received when the valve was in the full open position. This condition permitted the control room operator to stall the motor in atteatpts to fully open the valve. The resultant locked rotor current and subsequent insulation failure led to the motor failure. Since this valve performs a safety function, the redundant electrical protection features, such as thermal overloads and fuses, are deliberately sized so as to allow motor failure in efforts to operate the valve. The motor was rebuilt and the limit switches were reset. The valve was tested and found to operate satisfactorily.

No previous failures of this nature have occurred on this or similar valves. This occurrence did not affect safe operation since MO-2006, located upstream of MO-2008, was operabic and provide automatic isolation capability.

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9211200437 731107 PDR ADOCK 05000263 S PDR ,

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NOF 4ERN CTATED POWER CC .PANY o

. 2-twintenance procedures are being developed to assure proper adjustment of motor operated valve limit switches. In addition, the surveillance test procedures will be revised to caution the operators on exceeding the normal valve stroking times and the possibility of imposing a locked rotor condition on the motor operator.

Yours very truly, h.

L 0 Mayer, PE Director of Nucicar Support Services LQ4/br cc: J G Keppler G Charno f f Minnesota Pollution Control Agency Attn K Dzugan f