ML20003C838

Ro:On 810213,while Performing Reactor Startup,Nuclear Instrumentation Channel 3 Failed to Respond Positively to Changes in Reactor Subcritical Multiplication.Caused by Faulty Cable Installation.Cables Were Properly Connected

ML20003C838
Person / Time
Site:	University of Missouri-Columbia
Issue date:	03/13/1981
From:	Brugger R, Mckibben J MISSOURI, UNIV. OF, COLUMBIA, MO
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 8103180552
Download: ML20003C838 (2)

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Research Reactor Facility UNIVERSITY OF MISSOURI Re m Columbia. Missouri 65211 wepwe m aa242n March 13,1981 A"

g1 Director of Licensing /f 4 U. S. Nuclear Regulatory Commission Washington, D.C. 20555 y '

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Reference:

Docket 50-186 l .

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4 University of Missouri t7 License R-103 ^#

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Subject:

Report as required by Technical Specification 6.1.h(2). (.h,LD, Description On February 13, 1981 while performing a reactor startup, Nuclear Instru-mentation (NI) Channel 3, one of two period channels, failed to respond posi-tively to changes in reactor subcritical multiplication. Each period channel is required to provide a rod run-in at a 10 second period and a reactor scram at an 8 second period. With the instrument failing to respond correctly, the associated rod run-in and scram trips were inoperable, which is a deviation j from Technical Specifications 3.3.a and 3.4.c.

Analysis t During the reactor startup on February 13, 1981, the reactor operator noted l that N.I. Channel 3 indicated power level decreased while the source range, chan-l nel 2, and Channel 4 had increased due to subcritical multiplication. The console operator ceased rod withdrawal to investigate the Channel 3 detector compensation voltage setting, at which time the detector positive high voltage (HV) and negative HV cables were found reversed. The reactor was promptly shutdown by a manual scram at 231ti to comply with Technical Specifications 3.3.a and 3.4.c and the cable con-nections switched.

The reactor had been shutdown since 1345 on February 13, 1981 when N.I. Chan-nel 3 failed causing a reactor scram. To isolate the cause of the Channel 3 fail-ure, the three (3) cables that exit the drawer and go to the compensated ion cham-ber detector were exchanged with the same cables for the other period channel.

This was done to determine if the problem was associated with either the detector and cables or with the instrumentation drawer. The test indicated the problem was S

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Director of Licensing March 13,1981 Page 2 in the detector and cables so the cable connections into the drawers were re-installed on their respective drawers, but the positive (HV) cable and the com-pensation negative HV cable were reversed on Channel 3 due to them being termi-nated with the same type connector. The cables are marked as to taeir location (J6;+HV), (J7;-HV) by a white tag connected to the cable.

The failure of Channel 3 was due to pool water leaking into its detector drywell via a pin hole leak that had developed at the refuel bridge level. The drywell was repaired and tested, then the detector was installed with new cables.

Prior to reactor startup, the Channel 3 detector was response checked with a source to insure that it would respond.

There was no failure of the safety system, since N.I. Channel 2 was operable and would have provided the required rod run-in or scram protection due to high period.

Corrective Action As stated in the analysis, the reactor was shutdown and the cables properly connected. A front panel check was made on Channel 3 drawer verifying its op-erability. To avoid this problem, the high voltage connectors will be changed to use two different styles, which will mechanically prevent the cables from being -improperly connected.

Sincerely, ,

1[ <> E X f

. . -' J. C. McKibben Reactor ~ Manager Endorsement ,

Reviewed and approved: >

!s, .l/)'y;/ '. % :(q,u, R. M. Brugger  ! .!

Director j' JCMK:vs cc: James Keppler, Director Regulatory Operations - Region III N Document Management Branch, NRC Reactor Advisory Committee Reactor. Safety Subcomittee