ML20127G562

RO:721216,ground Fault Occurred on RHR Pump Motor.Caused by Failure of Air Deflector Located Near Base of Motor Due to Improper Installation

ML20127G562
Person / Time
Site:	Monticello
Issue date:	12/22/1972
From:	Mayer L NORTHERN STATES POWER CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9211170379
Download: ML20127G562 (2)

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NORTHERN STATE 5 POWER COMPANY Minneapolis, Minnesota 55401 co . Regulatory .Ello pyi v .

O C \tb December 22, 1972 kOg 7 h 'h,

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4 5h Mr. A. Giambusso /y .,3 ( [

Doputy Di rector for Reactor Projects i .7 N

Directorate of Licensing United S tates Atomic Energy Commission 10 1[IV 'f

I Washing con, D. C. 20545 l

Dear Mr. Giambusso:

MTICELLO f0 CLEAR GENERATlfD PLANT l Dockei No. 50063 License fb. DPR-22 R4R Pump Motor Failure 1

' A condition occurred at the Monticello Nuclear Generating Plant recently which we are reporting to your office in accordance with provisions of Section 6.6.B.3 l of Appendix A, Technical Specifications, of the Provisional Operating License DPR-22. The Region 111 Compliance Of fice has been notified of the occurrence.

On Saturday, December 16, 1972, a ground fault occurred on the #11 Residual Heat Removal Pump W tor. An investigation of the problem revealed that the ground fault was caused by the failure of an air deflector located near the base of the motor. Movement of the air deflector resulted in a small break in the insulation on one end turn of the stator coil. An inspection of the other three RHR pump motors revealed that the lower air deflector in the #13 RHR pump notor was severely cracked and hairline cracks were found on the lower air deflector for the #12 RHR pump motor. There was no evidence of crackl on the lower air deflector for the #14 RHR pump motor. Improper installai. so of the air deflectors is the suspected cause of the deflector failures; however, further investigation is being conducted. The #11 RdR pump had approximately 1325 hours0.0153 days <br />0.368 hours <br />0.00219 weeks <br />5.041625e-4 months <br /> of operation at the time the failure occurred. The #12 RHR pump had 177 hours0.00205 days <br />0.0492 hours <br />2.926587e-4 weeks <br />6.73485e-5 months <br /> of operation, the #13 RHR pump had 618 hours0.00715 days <br />0.172 hours <br />0.00102 weeks <br />2.35149e-4 months <br /> and the #14 RHR pump had 41 heurs. There was no evidence of any failure of the upper RHR pump motor air deflectors. The RHR pump motors are 600 hp, General Electric, T ri-Clad, ver ti-cal, high-thrust, three phase induction motors (Model #5K6329XC4A).

The stator coil end turn for the #11 RHR pump motor was repaired. A new air deflector was installed and the method of attaching the air deflector was s 9i fi ed. The modification included installation of a Textolite hold-down ring and eight additional hold-down bolts.

9211170379 721222 PDR S

ADOCK 05000263 PDR 7091

fjew air deflectors have been iris talled on the fLmber 12, 13, and 14 R:4R pamp mo tors usi ng t he codi fied hol d-down ar rangement. The Core S (Model //5K6338xC298) and the RHR Service Water pump notors (pray pump notorsModel #5K have been inspected and no evidence of air deflector failure was found. The deflector design of these motors is somewhat di f ferent than the RHR punp no to r s.

An Abnormal Occurrence Report will be available at the site for the Fegulaiory Operations inspectors.

Yours very truly,

, b.

L 0 Mayer, PE Di rector of tbclear Support Services U)M/kik i

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