ML19242C497

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Amended Deficiency Rept Re Malfunction of Pool Water Level Sensing Switch,Submitted by Defense Nuclear Agency.Switch Unit Replaced & Addl Sleeving Placed at Wear Point
ML19242C497
Person / Time
Site: Armed Forces Radiobiology Research Institute
Issue date: 07/31/1979
From:
ARMY, DEPT. OF
To:
Shared Package
ML19242C492 List:
References
NUDOCS 7908100483
Download: ML19242C497 (2)


Text

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MALFUNCTION OF POOL WATER LEVEL SENSING SWITCH Amended Report This report was prepared and forwarded to the Nuclear Regulatory Commission (NRC) pursuant to paragraph 4(a) of reactor license R-84 and Table I of the Technical Specifications.

L Description of Malfunction.

At 11:52 a.m. on 10 July 1979 a reactor oper Ator discovered that the float switch, which senses the reactor pool level, was not operabic.

IL Cause of Malfunction.

The malfunctic.n was caused by wear on the jacketing around the wires leading to che switch which provided a path to ground, thereby circumventing the switch function. A physical check of the switch function is part of the annual maintenance requirements and had been performed in February 1979 A physical check of t5- switch function had been performed on 26 June 1979, and it was found operable.

IIL Corrective Action Taken.

The switch unit was replaced and additicnal sleeving was placed at the wear point. It was back in service at 12:30 p.m. on 10 July 1979. It must be recognized that the circuitry which failed had been in continuous operation for over fifteen years without failure. and therefore is proven reliable. In order to insure that the function of this switch is acceptable in the future, a physical test will be performed at least monthly.

IV. Safety Evaluation.

This switch provides the scram signal which shuts down the reactor if the pool water level drops more than four inches. It is the only on-line scram for this parameter, but the level is checked visually each morning and a television monitor system is continuously available to the operator. In addition, there are anti-syphoning holes drilled in the intake and exhaust pipes for the primary system to prevent the pool from being drained by syphoning. The only other mechanism by which pool water could be lost would be a break of the tank wall in an exposure room. Loss of water through this Inethod would be indicatud by an alarm of R-1 of the area monitoring system.

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V. Safety Review.

The AFRRI Reactor and Radiation Facility Safety Committee n2et on 16 July 1979 and reviewed the initial repo-t. It recommended forwardmg to the NRC for information. This amendment is not substantially different in technical aspects from the original and will be reviewed at the ne.tt regular meeting.

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