ML20059M670

Advises That Shim 4 Did Not Return to Normal Position on 900918.Bearing-seal Assemblies Replaced Using Stainless Steel Bearings

ML20059M670
Person / Time
Site:	National Bureau of Standards Reactor
Issue date:	09/28/1990
From:	Rowe J NATIONAL INSTITUTE OF STANDARDS & TECHNOLOGY (FORMERL
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9010050177
Download: ML20059M670 (2)

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/ M<- e. \ Nellenal UNITED STATE 3 OE?ARTMENT OFCOMMNOR Instleute of Ctenalseele snel Teehnology I

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(301)~975 6210 FTS- 879 6210 . j FAX 921 9847 i

l September 2.;, 1990 1

i U.S. Nuclear Regulatory Commission Attention: Document Control Desk i Washington, DC 20555

Subject:

Information Letter, Docket No. 50 184 Gentlemen:

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i l- Last week, following' a routine chutdown, it was noted that shim No. 4 t did not return to its normal position a' the bottom. Normal bottom i

. position is usually below 1 degree and is always set below the. lower limit

! switch setting of about 2.5 degrees. In this case, the bottom indication was; about'1.9 degrees.

Last year the same phenomenon was -observed on shim No. 2. Other than ,

g that, the shim functioned and operated normally and. smoothly and met all release and drop requirements. After lengthy and extensive, investigation-L and repeated testing,, the problem was-traced to the inner bearing of the L, shaft. The bearing was replaced and the shim.has operated normally since i then, including bottom indication. It was intended at the time to replace-

g. the' bearings on the remaining three shafts at the next scheduled shim arm j

. replacement. At the same time, stsinless steel bearings were ordered to use-in place of the existing carbon steel bearings. It should be noted that this phenomenon had no effect on the performance of the shim, i

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Because of-the earlier indication on shim No. 2, the operating staff has become alert to watch for any similar changes in. bottom indication. -The rod seated signal comes off the lower ^11mit. switches and an annunciator is i actuated if any of the rods are not seated. Ordinarily, once all the lower limit switches are activated indicating the rods are seated, little

-attention was paid to'the bottom indication since it fluctuates about 0.5

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degrees. The operators.iamediately reported following a routine shutdown on_ '

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< a-Page'2-r Septe'mber 18, 1990,ithat the bottom position on shim No. 4 was outside the norm, even though the shim functioned-normally in all respects including the scram from 12 degrees. Further investigation revealed that the shim did not feel as smooth in the lower end upon manual move-ment, a feeling similar to that of shim No. 2 previously. Two months earlier shim No. 4 was- completely checked and found to perform normally..

The decision was .then made to. replace. the bearing on shim No. 4 as well as the bearings on the two remaining shims, No.- 1 and No. 3 and to use stainless steel bearing's if they arrived within a reasonable period of tire. Similar stainless steel bearings are used -in the wet parts of the slim arm assembly..

The bearing-seal assemblies on the three shims were replaced using stainless steel bearings. In general, the replacement operation was fairly smooth and with no serious problems encountered. Exposure to working personnel was low and kept to a minimum. Initial tests on the ,

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three shims indicate that they are functioning normally and smoothly.

Sincerely,.

Ot4rtl-  !

J. Michael'Rowe Chief, Reactor Radiation Division i

cc: Project Scientist  !

U.S. Nuclear Regulatory Commission  !

Region 1 .

475 Allendale Road King of Prussia, PA 19406 Project Manager

~Non-Power Reactor Directorate U;S. Nuclear Regulatory Commission 5 Washington, DC 20555 9

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