ML20248C711

RO 50-20/1989-2:on 890726,console Operator Received Abnormal Bldg Alarm.Leak Test Revealed Crack on Sys Ref Line Which Senses Atmospheric Pressure Outside Containment.All Polyethylene Tubing in Sys Replaced

ML20248C711
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	08/04/1989
From:	Bernard J, Kwok K MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
50-20-1989-2, NUDOCS 8908100125
Download: ML20248C711 (3)

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L t D NUCLEAR REACTOR LABORATORY: k AN INTERDEPARTMENTAL CENTER OF MASSACHUSETTS INSTITUTE OF TECHNOLOGY

' E O.K.' HARLING 138 Albany Street, ".ambndge, Mass. 02139 J.A. BERNARD. JR.

Director Telefax No. (617)253-7300 Director of Reactor Operations Telex No. 921473-MIT CAM Tel. No. (617) 253-4211 August'4, 1989 U.S. Nuclear Regulatory Corr..nission -

Washington, D.C. 20555 Attn: Document Control Desk-Subj ect : Reportable Occurrence 50-20/1989-2, Operation with an Inoperable Reactor BuildJng Overpress;sre Scram Gentlemen:

' Massachusetts Institute of Technology hereby submits'this ten-day report of an occurrence at the MIT Research Reactor in accordarce with paragraph 7.13.2(d) of the Technical Specificaticro. An initial re-port- was made by telephone to Region I (Mr. Douglas Dempsey) on 27 July 1989.

The format and conter.t of this report are based on. Regulatory .

Guide 1.16, Revision 1. )

1. Report No.: '50-20/1989-2 '

2a. Report Date: 4 August 1989 2b. Date of Occurrence: 26 July 1989

3. Facilitv MIT Nuclear Reactor Laboratory 138 Albany Street

' Cambridge, MA 02139

4. Identification of Occurrences i

The MIT Research ' Reactor was operated briefly on 26 July 1989 while the operability of the reactor building overpressure scram was uncertain. Technical Specification No. 3.5.6 rec,uires

.that a building overpressure scram be operable when the reactor j l is operating. The overpressure scram prevents reactor operation j i

if the building' pressure exceeds atmospheric pressure by more ]

than 3.0 inches of water. The building overpressure scram is a ]

part of the containment AP system. It is not part of the reactor j safety system. 7 hs a

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e 4 Reportable Occurrence 50-20/1989-2 Page 2 l

S. Conditions Prior to Occurrence

! The reactor was operating normally at 4.9 HW in accordance with the normal operating schedule. Scheduled experiments were in progress.  !

i i 6. Description of occurrence:

(- The console operator received the ' Abnormal Building AP' l alarm at 1428. The indicated containment AP was at -0.1" HO 2 (alarm set point). It then decayed to 0.0" H 0. (Note: Main-tenance of a negative building AP during operation is standard practice, but it is not a technical specification requirement j except during startups.) Upon investigation, the contaiment ven-tilation system was found.to be operating normally. An independ-ent AP reading was obtained through a valved penetration at the main personnel airlock by using a portable Magnehelic gage. A reading of -0.38" H0 was found. This established that the -

containment integrity was being maintained. The containment AP indication was briefly erratic but was restored to the correct value after some condensate was removed from one of the sens ir.g lines. The containment AP system operated normally for the next hour and then again failed to indicate correctly. The system was determined to be non-operational after further investigation.

The reactor was then immediately shutdown. This occurred at 1710.

7. Description of Apparent Cause of Occurrence:

Following the reactor shutdown, a leak test was performed on the air lines of the contalmnent AP system. .A crack was found on the AP system reference line which senses the atmospheric pres-sure outside of the containment. The crack caused the reference leg of the AP system to be affected by the pressure within the containment. The end result was that the indicated AP sensed by the system was less negative than the actual value. The building overpressure scram obtains its pressure signals from the same reference and sensing legs. The overpressure scram may therefore not have been operable during the period in which the system was investigated. ,

8. Analysis of Occurrence:

The building overpressure scram was last tested and cali-brated on 30 June 1989. The scram was set conservatively at i 1.98" H2 O which is more than an inch below the setpoint required by the technical specifications. Given this margin it is believed that the scram was fully operable until the containment )

AP system was determined to be non-operational immediately prior I to the reactor shutdown.

f The cause of the crack in the sensing line w is embrittle- {

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I-g Reportable Occurrence 50-20/1989-2 1

Page 3 ment. The polyethylene tubing was protected from external damage by standard electrical conduits. The reference line in which the crack occurred was made of polyethylene tubing manuf actured by Imperial Eastman. The tubing was installed in 1975 and was found to have becomo hardened. The failed section of the tubing (and only that section) was exposed to a radiation level of about 50 R/hr. The total dose over the fourteen year period was about 6 Mega Rads which is below the recommended design dose of 10 11eg a Rads as stated in the Military Standardization Handbook for Plastics, Raport No. MIL-HDBK-700(MR).

Containment integrity was maintained at all times during this occurrence. Also, the building AP was negative at all times during this occurren'9.

9. Corrective Action:

The corrective action consisted of immediately shutting down the reactor and replacing all polyethylene tubing in the contain-ment AP system. The system was then leak checked and the build-ing overpressure scram was calibrated. The system was then returnad to service and observed to be operating properly.

10. Failure Data:

There have been no telated occurrences.

Sincerely, Kwan S. Kwok Superintendent 4

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John A. Bernard, Ph.

Director of Reactor Operations KSK/gw cc: MITRSC USNRC - Region I - Chief, Reactor Projects Section IB USNRC - Region I - Proj ect Inspector, l Reactor Projects Section IB USNRC - Senior Resident Inspector, Pilgrim Nuclear Station l

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