ML20062D302

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on 781102 During Routine Test,Shim Arm 1 Had Drop Time in Excess of Acceptable Range Caused by Slightly Longer Clutch Release.Assembly Removed & Snap Ring on Armature Hub Replaced in Favor of a More Uniform Support
ML20062D302
Person / Time
Site: National Bureau of Standards Reactor
Issue date: 11/07/1978
From: Rozier Carter
COMMERCE, DEPT. OF
To: Stello V
Office of Nuclear Reactor Regulation
References
NUDOCS 7811210320
Download: ML20062D302 (8)


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UNITED STATES DEPARTMENT OF COMMERCE S4 4.j;-

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National Bureau of Standards wasn:ngton, c.c. 2C234

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Mr. Victor Stello

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Director, Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Mr. Stello:

On November 2,1978, during routine surveillance tasting, shim arm No. I had a drop time of 180 msee for the first 5' which is 5 msec longer than the acceptable 175 msec. The tests were repeated the following day and the drop times ranged from about 175 to 190 msec. Examination of the drop tracs showed the delay was due to slightly longer clutch telease time which means that the armature (clutch disc) was not leaving the field fast enough. Examination of the drive assembly did not show any-thing significant. It was possible that the armature may have been slightly cocked which could be a small contributing factor.

The assembly was removed. The snap ring on the armature hub was replaced with a more uniform support. The thin cadmium coating between the arma-ture and hub was removed and the surface.s polished in order to allow freer movement. The assembly was reinstalled and tested. The 5* drop time was an acceptable 160 maec.

Sinc 7ely, 7 x . / d ~~

y,x n. - :, i Robert S. Carter Chief, Reactor Radiation Division

! cc: Director, Region 1, U.S. NRC l

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-811210 M

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