ML19310A303

Ro:On 800516,w/reactor Operating at Full Power in Automatic Mode,Automatic Regulating Blade Drive Mechanism Was Discovered Producing Grinding Noise.Caused by Worn Spot on Drive Gear.Regulating Blade Gear Drive Was Replaced

ML19310A303
Person / Time
Site:	University of Missouri-Columbia
Issue date:	06/04/1980
From:	Brugger R, Mckibben J MISSOURI, UNIV. OF, ROLLA, MO
To:
References
NUDOCS 8006110064
Download: ML19310A303 (2)

Text

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JE UNIVERSITY OF MISSOURI ,

Research Reactor Facility Columbia. Missouri 65211 June 4, 1980 Telephone p14) 8824211 Director of Licensing U. S. Nuclear Regulatory Comr.ission Washington, D. C. 20555

Reference:

Docket 50-186 University of 'd ssouri License No. R 103

Subject:

Failure of the Automatic Regulating Blade Drive Machanism Description 1 On May 16, 1980 with the reactor operating at full power in the automatic mode, a grinding noise was heard from the automatic regulating blade drive mech-anism. Control Room indication. for the blade was observed to be stationary at 12.83 inches. The reactor was immediately shutdown by rod run-in.

The reactor had been operating at full power in automatic control with the i regulating blade properly maintaining power for a period of 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> preceding the failure. The reactor was shutdown in accordance with Techni. cal Specifi-cation 3.2.a at the time of failure.

Analysis The regulating blade controls reactor power at a desired level set by the operating crew. The blade is constructed of stainless steel and drives at 40 inches per minute. It controls power by balancing the signal received from one of the nuclear instrument channels to a potentiometer set by the operating crew. This blade is frequently making minor adjustments to maintain power at the desired power level. Reviewing the nuclear instrumentation chart recorders showed that the regulating blade had been properly maintaining desired power until the reactor was shut down.

A visual inspection of the gear drive unit mounted on the drive motor shaft revealed a worn spot on a drive gear causing the motor to fail to drive the blade. This explained the loud grinding noise that was heard when the regulating blade failed.

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% COLUMBIA KANSAS CITY ROLLA ST. LOUIS an equal opportunity institution i 8 0 0 6110 0H 3 j

Director of Licensing June 4, 1980 Page 2 Corrective Action The regulating blade gear drive assembly was immediately replaced.

Following replacement, the regulating blade was cycled through its full travel assuring proper operation of the blade and all functions derived from the blade position. The portion of the compliance check associated with rod run-ins initiated by regulating blade Iosition was checked satisfactorily.

,f; Sincerelyg/ l

- 4 ' J,4}lw

(' J. C. McKibben ,

Reactor Manager )

i Endorsement Reviewed and approved l

/

Robert M. Brugger Director JCMK:vs cc: James Keppler, Director Regulatory Operations - Region III Reactor Advisory Connittee Reactor Safety Subcommittee e