ML20062D302
| 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 National Bureau of Standards 4.j;-
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Mr. Victor Stello 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,
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- n. - :, i y,x Robert S. Carter Chief, Reactor Radiation Division cc: Director, Region 1, U.S. NRC l
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