ML19323D508

RO 50-20/80-1:on 800322,initial Rept Was Made Re Failure of Outer Door of Truck Airlock to Maintain Leak Rate of Bldg Containment Limits.Caused by Seal Leak in Outer Door. Door Will Not Be Routinely Opened Until Gasket Is Replaced

ML19323D508
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	04/25/1980
From:	Bernard J MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE
To:
References
NUDOCS 8005210624
Download: ML19323D508 (4)

Text

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f f f NUCLEAR REACTOR LABORATORY l MASSACHUSETTS INSTITUTE OF TECHNOLOGY '$[M oM.HARUNG 138 Albany Street Cambridge, Mass. 02139 L CLARK. JR.

o'ractor (617)253-42 11 Director of Reactor operahons April 25, 1980 Mr. Boyce H. Grier, Director U.S. Nuclear Regulatory Commission l Region #1 631 Park Avenue King of Prussia, Pennsylvania 19406 Attention: Mr. E. Greenman, Reactor Inspector Re: Reportable Occurrence 50-20/80-1, License R-37: Inability of the Outer Door of the Truck Lock to Maintain Containment Integrity Gentlemen:

1 Massachusetts Institute of Technology hereby submits this 10 day report of an occurrence at the MIT Research Reactor in accordance with Paragraphs 7.13.2d, 1.15.1, and 3.7.1 of the Technical Specifications.

An initial report was made by telephone to Region #1 (Mr. T. Stetka) on April 22; 1980.

The format and content of this report is based on Regulatory Guide 1.16.

1. Report No. 50-20/1980-1

2. a) Report Date: April 25, 1980 b) Date of Occurrence: April 19, 1980 - (Test data taken.)

April 22, 1980 - (Computer analysis of test data complete.)

3. Facility: M. I. T. Research Reactor 138 Albany Street Cambridge, Massachusetts 02139

4. Identification of Occurrence: Failure of the outer door of the truck airlock to maintain the leakage ra::e of the building containment at less than one percent of the contained air volume per day per psig pres-sure as specified by Technical Specification 3.5.2.

5. Conditions Prior to Occurrence: A normal reactor shutdown had been conducted at 0700 April 18, 1980 in order to perform a measurement of the containment building leak rate. This measurement is performed I annually as required by Technical Specification 4.2.l(a).

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Reportable Occurrence Report April 25, 1980 Page 2

6. Description of Occurrence: Preparations for the containment building leakage rate measurement began at 1000 April 18, 1980 in accord with approved test and calibration procedures. The test is conducted in two separate phases so that each isolation device of any building pene- )

tration that is equipped with a double closure may be tested separately.

This is done in order to demonstrate that containment integrity is ,

maintained even when one isolation device of a double-closure facility  !

is open. This permits the use of airlocks for entry to and from the i building while the reactor is at power.

l Data from the second phase of the test, which was initiated at 0130 {

April 19, 1980, indicated that an excessive leak rate of approximately l 1.7 times permissible existed. Investigation showed that the high {

1eakage was occurring at the gasket of the outer door of the truck lock. i Accordingly, the inner truck lock door, which had been successfully {

tested during the first phase of the test and which had been opened to allow testing of the outer door during the second phase, was closed. '

The second phase of the test was restarted and successfully completed.

The two phases of the test demonstrated that all containment building closures except the outer door of the truck airlock were capable of maintaining containment integrity.

7. Description of Apparent Cause of Occurrence: This occurrence was due to leaks in the seal of the outer door of the truck airlock. The de-tected leaks are located on the side of the door nearest the restricted area fence.

8. Analysis of the Occurrence: The outer truck lock door's gasket is' physi-cally attached to the seating surface of a rigid metal frame that is en-bedded in the concrete structure that forms the truck lock. The truck lock's outer opening is sealed by six hydraulic rams that force the door against the gasket. There are three rams on each side of the 12.5 foot high door. Inasmuch as they are located at the bottom, middle, and top of each side, they do not apply a uniform force to the entire door. The force is strongest over the area directly under a ram and weakest at the points intermediate between any two rams.

The current gasket for the outer truck lock door was installed approxi-mately one year ago on April 30, 1979. The gasket is normally made of soft rubber. Being ductile, the rubber readily deforms under the non-uniform loading of the rams and seats the truck lock door. However, on this occasion, a harder grade of rubber had been used with the idea that it would not wear down as rapidly as did the softer material. Subsequent to the gasket replacement, the new gasket was tested as a part of the 1979 pressure test. It did not pass on the initial test trial, was re-worked, and was successfully tested.

i Reportable Occurrence Report April 25, 1980 Page 3 Since the gasket did not pass the April 19, 1980 pressure test, it is not clear that the outer truck lock door could be considered as a satis-factory seal at all times between the May 1979 and the April 19, 1980 test. The truck airlock is not routinely required for the conduct of reactor operations and is normally only used when the reactor is secured and conditions are such that containment integrity is not required. It is believed that the outer door of the truck airlock was only relied upon to provide containment integrity three times in the past year.

Each occasion lasted approximately fifteen minutes and all occurred dur-ing the period January - February 1980. No events occurred during any of these periods that would have necessitated the sealing and the isola-tion of the containment building. There were no occasions during the past year when excessive pressure existed within the building.

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9. Corrective Action: The immediate corrective actions consisted of: l l

(a) Placement of a " CAUTION" tag on the power supply to the truck air-lock. The tag states that the inner door of the truck airlock should not be opened unless containment integrity is not required. j (The power supply itself is, and has been, in an area that is always locked while the reactor is in operation. The console opera-tor is in possession of the only key.)

(b) Circulation to all licensed, maintenance, and electronic personnel of a memo stating the conditions under which the inner door of the truck airlock can be opened. Signed copies of this memo have been returned to the Superintendent by all individuals who might use the truck lock.

(c) Inspection of the metal door surfaces for evidence of wear. None was found.

Permanent corrective action will consist of: l (a) Replacement of the existing gasket with one of the proper hardness.

(b) Repetition of the air leakage test on the outer door of the truck lock upon installation of the new gasket.

Subsequent actions will depend on the results of the leakage test. If the new gasket fails or is marginal, consideration will be given to either reanalyzing the outer truck lock door or to developing a reliable procedure to properly seat the gasket. Restrictions on the use of the.

inner door would, of course, remain in effect while either of these op-tions was pursued. If the new gasket passes the leakage test, the test will then be repeated in several months. A decision will be made at

that time as to whether or not the frequency of the leakage test of the 1

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Reportable Occurrence Report April 25, 1980 Page 4 truck lock should be permanently increased or continued on an annual basis. Inasmuch as the outer door always passed the leakage test when it was equipped with a gasket of the proper hardness, it is expected that the annual test will be sufficient.

10. Failure Data: No previous failure data for this gasket is recorded Prior to 1979 at the facility.

Sincerely, O

John Bernard Director of Reactor Operations (Acting)

JB:DKE cc: MITRSC USNRC-0MIPC I

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