ML20084V175

Ao:On 720128 Control Rod Drive Mechanism 35 Would Not Withdraw More than 107.2 Inch.Caused by Improper Operation of Motor Package Brake.Mechanism 35 Will Be Aligned & Motor Package Will Be Removed & Examined

ML20084V175
Person / Time
Site:	Palisades
Issue date:	02/07/1972
From:	Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084V179	List: ML20084V175 ML20084V199
References
NUDOCS 8306290978
Download: ML20084V175 (2)

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49 General Offices: 212 West Michigan Avenue, Jackson. Michigan 49201. Area Code 517 788-0550 February 7, 1972 Dr. Peter A. Morris, Director Re: Docket No 50-255 Division of Reactor Licensing License No DPR-20 United States Atomic Energy Commission Washington, DC 20545

Dear Dr. Morris:

This letter is written to apprise you of an incident that occurred January 28, 1972 at the Palisades Plant, involving the motor package of control rod drive mechanism (CRIM) No 35 Plant Condition at the Time of the Incident At the time the incident occurred, the reactor was operating at 20 ercent of rated thermal power with a generator electrical output o approximately 106 MWe (gross). Testing was in progress which in-volved increasing primary system boron concentration. Regulating Groups 3 and 4 were being withdrawn by the automatic rod control system to the upper electrical limit and 66 inches, respectively, to overcome the bcron additions.

Descriptica of the Incident Regulating Group 3 (includes No 35) was being withdrawn in the automatic mode to overcome boron addition, when a 4-inch rod deviation alarm was received. A check of the individual rod position indication f of the CRDM in regulating Group 3 revealed that CRIM No 35 had stopped g /f at 107 2 laches. During this check of the position indication, an 8-inch rod deviation alarm was received and the remaining CRDM in the group were

$1 withdrawn to 118 inches before reaching power equilibrium, hg An unsuccessful attempt was made to withdraw CRDM No 35 in the g manual individual mode. CRDl/ No 35 motor package fuses were changed and another unsuccessful attempt was made to withdraw No 35 The CRDM was NII then successfully inserted about an inch and then withdrawn in the manual individual mode to its proper place with regulating Group 3 fth The testing was continued with additional boration and success-fully completed with regulating Group 3 at its upper electrical limit and regulating Group 4 at 66 inches. All further CRDM operations were normal.

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\/ 'wi Dr. Peter A. Morris 2 Docket No 50-255 February 7, 1972 The malfunction of CRIM No 35 was essentially identical to the malfunction of CRIM No 39 which occurred December 23, 1971 and was re-I ported by letter dated December 30, 1971. It was concluded that the problem was due to the intermittent or improper operation of the motor package brake.

\, Corrective Action As described above, CRDM No 35 was aligned with the CRDM in regu-lating Group 3 and operated normally when the regulating group was with-drawn to the upper electrical limit. Regulating Group 3 remained fully withdrawn until February 3, when a reactor trip was experienced due to a feed-water transient. CRDM No 35 operated normally on the reactor trip, as did all other CRDM.

The motor package for CRDM No 35 will be removed and examined during the current plant outage. Prior to returning the plant to service, CRIM No 35 will be tested for trip times and motor running currents. Any defects detected during the examination and testing will be corrected.

Conclusions This incident and future incidents of a similar nature do not compromise reactor safety because the CRDM is still capable of being tripped.

A failure in the motor package does not prevent proper functioning of the clutch unit. The de-energizing of the clutch separates the motor package from the remainder of the CRIM.

The effects of operation with one or more inoperable CRDM have been considered. Appropriate operating limitations are incorporated in the Technical Specifications to insure that hot channel factors and ejected rod worth limits are met. A similar occurrence could not go undetected because of the two rod deviation alarms.

Yours very truly, Ralph B. Sewell (Signed)

RBS/ map Ralph B. Sewell Nuclear Licensing Administrator CC: Boyce H. Grier USAEC

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