ML20206P532

Ro:On 981229,only One Nuclear Safety Period Scram Channel Was Operable,For Period of Five Minutes.Caused by Placement of Nuclear Safety Sys Channel 1 Input Signal Cable on Wrong Bnc Connector.Placed Channel on Correct Bns Connector

ML20206P532
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	01/06/1999
From:	Bernard J, Lau E, Newton T MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9901120137
Download: ML20206P532 (3)

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NUCLEAR REACTOR LABORATORY -

AN INTERDEPARTMENTAL CENTER OF _  ;

MASSACHUSETTS INSTITUTE OF TECHNOLOGY --

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JOHN A. BERNARD 138 Albany Street, Cambridge, MA 02139-4296 Activation Analysis Director 9erectorof Reactoroperahons Telefaz No. (617g7g, Coolant Chenpstry Tel. No. (617) Nuclear Medicine Pnncipal Research Engineer Reactor Engineenng 1

January 6,1999 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 l i

Attn.: Document Control Desk

Subject:

Reportable Occurrence 50-20/1998-2, Operation With Fewer than the Required Number of Nuclear Safety Channel Period Scrams Gentlemen:

The Massachusetts Institute of Technology hereby submits a report of an  ;

occurrence at the MIT Research Reactor (MITR) in accordance with paragraph 7.13.2(d)  !

of the Technical Specifications. An initial report was made by telephone to NRC Region I on December 30,1998.

The format and content of this report are based on Regulatory Guide 1.16, Revision 1.

1. Report No.: 50-20/1998-2 2a. Report Date: 6 January 1999-2b. Date of Occurrence: 29 December 1998 \7 .:

3. Facility: MfT Nuclear Reactor Laboratory 138 Albany Street Cambridge,MA 02139

4. Identification of Occurrence: '

For a period of five minutes, during a startup to low power of the MIT Research Reactor, only one nuclear safety period scram channel was operable.

Technical Specification No. 3.7 requires that there be at least two such operable channels while the reactor is operating.

5. Conditions Prior to Occurrence:

. Full power instrumentation and mechanical checklists had been completed prior to the startup. Safety Channels #1-3 provide an automatic shutdown on short reactor period. Channels #1 and #2 consist of both a fission and ion chamber.

Channel #3 is comprised only of an ion chamber. For a reactor startup, the fission chambers of channels #1 and #2 are initially operable. As the startup proceeds, the neutron level in the reactor increases because of subcritical multiplication. As a 9901120137 990106 PDR ADOCK 05000020 S . P OR _

. ' Reportable Occurrence 50-20/1998-2 Page 2 of 3 i

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l result, the ion chambers become operable and the instrumentation is shifted by

adjusting gains / discrimination settings to the ion chambers. The sequence is:

1. Channei #1 and #2 fission chambers operable.

2. Channel #3 ion chamber on scale. .  :

3. Shift Channel #1 to ion chamber. (Ch. #2 and #3 operable)

4. Channel #1 ion chamber operable.

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~5. Shift Channel #2 to ion chamber. (Ch. #1 and #3 operable) j 6.- Channel #2 ion chamber operable.

The act of shifting from fission to ion chamber causes the affected channel to be inoperable for a short interval, five minutes or less.

6. Descrintion of Occurrence:

At 2233 on December 29,1998, a reactor startup was commenced on d.e MIT Research Reactor. At 2255, channel #3 was declared in service, and channel

1. 1 fission chamber was shifted to ion chamber. At that time channels #2 and #3 were operable. At 2256 channel #1 was declared in service and channel #2 fission chamber was shifted to ion chamber. However, channel #1:was'not fully operable in that while it was indicating properly, its scrain function was not functional.

Hence, the reactor was operating with only the channel #3 nuclear safety. system j l period scram. Channel #2 was declared operable at 2301, resulting in two nuclear

. safety system period channel scrams being operable in accordance with Technical l Specification 3.7. The reactor was operated for a total of 5 minutes (2256 to 2301) l

with~only one operable period automatic scram. The reactor power was at about 20 1

kW at the time. l l 1

~7. Descriotion of Apparent Cam of Occurrence: ,

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The procedure listed above in section 5 of this report ensures that two

m. clear safety system period scrams are operable at all times. The switching of input from a fission chamber to an ion chamber may induce a period transient that can be positive and of a high enough magnitude to induce electronic indication of a protective action Accordingly, at 2255, the input to the channel #1 nuclear safety system was temporarily removed by disconnecting the input signal cable from its BNC connector on the back of the chassis. When the induced period transient had decreased to a level below the scram setpoint, the operator reconnected the input signal to an incorrect BNC connector on the same chassis, disabling nuclear safety system channel #1. Thus, the immediate cause of this occurrence was the r placement of the nuclear safety system channel #1 input signal cable on the wrong L BNC connector. This incorrect placement of the mput cable was noticed and I corrected by an operator at 0930 on December 30,1998.

[ The incorrect BNC connector is unused by the chassis. All personnel were j aware that it was unused and the operating crew ho conducted the startup on 4

12/29/98 had in fact discussed the importance of reconnecting the signal to the

[ correct cc,anector and rehearsed the procedure. The root cause of the occurrence

was therefore a design error in that en unused connector was left installed on the chassis.

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.- Reportable Occurrence 50-20/1998-2 Page 3 of 3.

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8. Annivsis of Occurrence:

On December 29,1998, the MIT Research Reactor was operated for a total  !

of five minutes with only one of two required number of period scram channels l Indication of reactor period was available on two channels at all times. Also, three i other safety channels provided automatic protection against a high power level at all '

times (only two are required).

9. Corrective Action: ,

- The immediate corrective action consisted of placing the nuclear safety l system period channel #1 input signal cable on its correct BNC connector and placing a cap on'the incorrect connector. The permanent corrective action will consist of physically removing the unused BNC connection from the nuclear safety system chassiss' o that only the correct connector will be present. This action will be completed during our next maintenance outage, now scheduled for March or April IV)9. In addition, all other safety system channels'have been checked for unused connectors. None were found.

10. Failure Data-None.

Since ..

YY Q Lc l

omas H. Newton, Jr., PE Edward S. Lau, NE -

i sst. Superintendent for Engineering Asst. Superinter. int for Operations

• MIT Resean:h Reactor MIT Research Reactor

,(c6/ '

chn A. Bernard, Ph .

Director i MIT Nuclear Reactor Laboratory '

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' JAB /gw . t cc: MITRSC

(

I USNRC - Senior Project Manager,

NRR/ONDD '

USNRC - Region I- Project Scientist, I i Effluents Radiation Protection Section (ERPS)

!- FRSSB/DRSS i

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