ML19274D312

States That on 781219,while Performing Reactor startup,1 of 3 Nuclear Instrumentation Power Range Channels Failed to Respond to Changes in Reactor Power.Caused by 2 Cable Connectors Which Were Only Partially Threaded

ML19274D312
Person / Time
Site:	University of Missouri-Columbia
Issue date:	01/15/1979
From:	Alger D MISSOURI, UNIV. OF, ROLLA, MO
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 7901230152
Download: ML19274D312 (2)

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Research Reactor Facility UNIVERSITY OF MISSOURI g,3,,,ch Park Columbia. Missouri 65201 January 15, 1979 Tetephone (314) 8824211 Director of Nuclear Reactor Regulations U. S. Nuclear Regulatory Conmission Washington, D. C. 20555

Reference:

Docket 50-186 University of Missouri License R-103

Subject:

Failure of Nuclear Instrumentation Channel 6 Description On December 19, 1978 while performing a reactor start up, Channel 6, one of three Nuclear Instrumentation (N.I.) Power Range Channels, failed to respond to changes in reactor power. Each power range channel is required to provide a rod run-in at 115% of full power and a reactor scram at 125% of full power.

With the instrument failing to respond, its associated rod run-in and reactor scram trips were inoperable, which is a deviation from Technical Specifications 3.3.a and 3.4.c.

Analysis On December 18, during a routine maintenance day, the N.I. Channel 6 un-compensated detector chamber and both coaxial cables were replaced. As part of the start up following the maintenance, the reactor was brought to a steady power level of 5 MW at 0049, December 19, 1979, to make a comparison between the nuclear instrumentation indicated power and the indicated heat balance, as required by the Standard Operating Procedurc3. N.I. Power Range Channels 4 and 5 were in agreement with the heat balance but Channel 6 was not indicating.

An attempt was made to relocate the detector drywell to increase Channel 6 indication, but the instrument did not respond; therefore, the reactor was shut down by initiating a manual rod run-in at 0055 to comply with Technical Specifications 3.3.a and 3.4.c.

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Director of Nuclear Reactor Regulations January 15, 1979 Page 2 The two HN cable connectors for Channel 6 were found only partially threaded, which prevented the center pin from making good electrical contact. After both connections were securely tightened, the 50 KW power range modules were inserted and the instrument was response checked with a high level gamma source. Then the 10 MW power range modules were reinserted, and a front panel check of the instrument was made verifying the instrument circuitry was still operating properly.

There was no failure of the safety system, since N.I. Power Range Channels 4 and 5 were operational and would have provided the required rod run-in or scram protection.

Corrective Action As stated in the analysis, the reactor was shut down and the problem corrected. The occurrence has been reviewed by both the Electronic Techni-cians and the operating staff. A standing order has been issued to require performing a response check of a detector any time work is performed on the detector or its associated cables prior to reactor start up.

Sincerely, o

a J. C. McKibben Reactor Manager

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Don M. Alger Associate Director JCMK:vs cc: Directorate of Regulatory Operations, Region III Reactor Advisory Committee Reactor Safety Subconnittee