ML20235G499

Ro:On 870825,closed Indicating Light for Automatically Closing Reactor Containment Isolation Door Did Not Turn On. Caused by Addl Drag Reducing Coast Distance of Door.Motor Drive Stop Microswitch Readjusted

ML20235G499
Person / Time
Site:	University of Missouri-Columbia
Issue date:	09/24/1987
From:	Alger D, Mckibben J MISSOURI, UNIV. OF, COLUMBIA, MO
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 8709300072
Download: ML20235G499 (3)

Text

Research Reactor Facility UNIVERSITY OF MISSOURI September 24, 1987 Research Park Columbia, Missouri 65211 Telephone (314) 882-4211 U. S. Nuclear Regulatory Commission ATTENTICH: Director Standardization & Non-Power Reactor Project Directorate Office of Nuclear Reactor Regulation Washington, D. C. 20555

REFERENCE:

Docket 50-186 University of Missouri Research Reactor License R-103 ,

SUBJECT:

Report as required by Technical Specification 6.1.h(2) concerning reactor operation with the operability of an automatically-closing reactor containment isolation door in a degraded condition.

INTRODUCTION The reactor was operated from 0510 August 25, 1967 to 0700 August 27, 1987 with reactor containment integrity in a state of reduced effectiveness due to the uncer-tainty of tne operability of one ventilation system automatically-closing door (door 504). No containment building isolations were required during this time period and the automatically-closing backup door to door 504 was operable.

Technical Specification 3.5(a) requires that containment integrity be maintained at all times except when the reactor is secured and irradiated fuel with a decay time of less than sixty days is not being handled. The Technical Specification definition of reactor containment integrity (1.15) lists six conditions which must be met for containment integrity to exist. One of these conditions is that "all containment building ventilation system automatically-closing doors and automatically-closing valves are operable or placed in the closed position." The Technical Specification definition of operable (1.12) states "that a system is operable when it is capable of performing the intended function in a normal manner."

DESCRIPTION On August 25, 1987 the reactor containment isolation system was tested as part of a normal prestartup checksheet prior to reactor startup. When the containment isola- l tion was initiated, the closed indicating light for one of the two ventilation system automatically-closing doors (door 504) did not turn on. Other items indicated the door had driven at least part way closed. The open light had turned off and the doors were heard being driven closed. Additionally, the ventilation fan had been properly turned off by a microswitch connected to the door. An operator went to investigate the 8709300072 870924 PDR ADOCK 05000186 k .f P PDR 9 0 m i a o g4 4 COLUMBIA KANSAS CITY ROLLA ST. LOUIS U enau=nos,wnsmunon \ l

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U. S. Nuclear Regulatory Commission September 24, 1987 >

Page 2 position of door 504 Door 504 was in the closed position, but he found that by pushing on the door it moved an additional 1/4" to 1/2" in the closed direction and heard the door 504 seal gasket inflate. The control room door 504 indication now indicated " closed."

An operator in the control room then cycled both doors 504 and 505 several times j by initiating a series of reactor isolations. Each time the doors closed and the l

closed indicating light turned on. Since the problem could not be reproduced, he did not investigate further at that time. What was thought to be a singular electronics problem was noted and a request for an electronics technician to investigate the problem on the subsequent maintenance day, August 27, 1987, was turned over to the l oncoming shift. ,

On August 27, 1987, with the reactor shutdown for maintenance at 0700, a repeat test of the isolation doors was conducted. On the door's first closing sequence, the door 504 closed indication light did not turn on again. A reactor operator and an electronics technician investigated the absence of a door 504 " closed" indication. Door 504 was in the closed position, but they again found that by pushing on the door it moved an additional 1/4" to 1/2" in the closed direction and heard the door 504 seal gasket inflate. The control room door 504 indication now indicated " closed." At this time it was realized that the problem was more than a singular electronics problem. j i

There are two microswitches that must be actuated during the normal closing sequence of door 504. One stops the door drive motor and allows the door to coast I approximately 6 inches to its closed position. A second inflates the door seal once the door is closed. Both microswitches are actuated by a cam assembly driven by a j chain and sprocket driven by the door operating system. The door 504 closed indication l 1s actuated by the closed position microswitch in series with a pressure switch sensing door 504 seal pressure. This actuation is used since it indicates the door is closed and the seal has inflated.

The Reactor Plant Engineer and Chief Electronics Technician were asked to assist in determining the cause of the problem. By disengaging the motor drive and pushing the door through its closing sequence, they observed the microswitch actuation points. They determined that the travel distance between the motor power stop microswitch and the seal inflation microswitch was a little less than six inches. Each microswitch cam was i verified tight and secure, nonbinding and operating in its intended fashion. The only (

possible explanation for why the door did not travel on the two occasions far enough l to pick up the seal inflation microswitch is there may have been additional drag then i reducing the coast distance of the door.

A coiled electrical cable attached to the door safety edge could catch on the underside of a duct brace and may have applied a varying degree of drag to the door as it closed. This cable was relocated to remove any possible drag.

1 ANALYSIS The automatically-closing door (door 504) is one of two such doors in the con-tainment ventilation system. These doors (504 and 505) are located in the containment building fifth level. Each of these doors has a backup to provide redundancy in case l

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U. S. Nuclear Regulatory Commission September 24, 1987 Page 3  !

I of inoperability of door 504 or 505. The backup doors were added to the containment building prior to granting the R-103 license for 5 MW in 1967 and are discussed in Hazards Summary Report Addendum 2. All doors are open during normal reactor opera- ,

tion to allow supply and return fans (RF2 and SF2) to recirculate the containment (

building air and to add fresh air from outside. These doors are designed to close automatically when a reactor isolation is initiated.

The basis for Technical Specification 3.5(a) is to assure that the containment building can be isolated at all times except when the plant conditions are such that the probability of release of radioactivity is negligible. There is uncertainty if the door 504 was fully operable during the time interval, but the containment building isolation safety system was still capable of performing its safety function due to the j

. containment ventilation backup doors were operable.

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CORRECTIVE ACTION l The motor drive stop microswitch was readjusted to a position that allowed the door to travel 1" beyond the point required to actuate the gasket inflate microswitch. The safety edge coiled electrical cable was relocated to remove any possible drag. Door operability was tested many times af ter this adjustment and has been tested satisfac-torily on prestartup checks on August 29, September 3, September 10, and September 17, 1987.

Sincerely, i

J. C. cKibben Reactor Manager Endorsement:

Reviewed and Approved M  %

Don M. Alger Associate Director xc: Document Control Desk ,

Regional Administrator, Region III Reactor Advisory Committee

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