ML20236S493

RO 50-20/1987-2:on 871110,improper Performance of Reactor Reshim Resulted in Excessive Power Rise.Caused by Operator Error.Operator Suspended from All Licensed Duties Pending Further Review of Circumstances & Disciplinary Measures

ML20236S493
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	11/19/1987
From:	Bernard J, Lisa Clark, Kwok K NUCLEAR REACTOR LABORATORY
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
50-20-1987-2, NUDOCS 8711250203
Download: ML20236S493 (4)

Text

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.: NUCLEAR. REACTOR LABORATORV -

AN INTERDEPARTMENTAL CENTER OF  %)*Ky((

MASSACHUSETTS INSTITUTE OF TECHNOLOGY >

l O K. HARLING 138 Albany Street Cambridge, Mass. 02139 L CLAHX, JA.

Director (617) 253-4 2 1 1 Director of Reactor Operations g

Nove$1ber 19, 1987 l

i U.S. Nuclear Regulatory Commission ,

l i Attn: Document Control Desk Washington, D.C. 20555 Subj ect: Reportable Occurrence 50-20/1987-2, Improper Reactor Reshim Causing an Excessive Power Rise l Gentlemen:

Massachusetts Institute of Technology hereby submits this ten-day report of an occurrence at the MIT Research Reactor in accordance with paragraph 7.13.2(d) of the Technical Specifications. An initial re-port was made by telephone to the NRC Headquarters Operations Of ficer, The occurrence was referred td Mr. Ray Smith on 11 November 1987.

Mr. Ted Michaels by the . Headquarters Office. It was discussed 'with Mr. Michaels on 12 November 1987. A further report of this occurrence was made by' telephone to Region I, Mr. Larry Doerflein, on 13 November 1987.

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

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1. Report No.: 50-20/1987-2 , l 2a. Report Date: 19 November 1987.

v 2b. Date of_0ccurrence: 10 November 1987 ,

3. Facility: MIT Nuclear Reactor Laboratory ,

138 Albany Street H Cambridge, MA 02139 i

4. Identification of Oc_currence:

Improper performance of a reactor restAiro e.o that as a, result of manual withdrawal of a shim blade, , the reactor's peatronic power rose f rom 4.71 MW to 5.18 MW at which level the safety sys-tem caused an automatic shutdown. This occuricL 4t 1523 10 /

November 1987. The reactor's thermal power, which is continunos-ly computed by a calorimetric balance . o r.d recorded, never exceeded 4.71 MWt.

8711250203 871119 '

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s Reportable Occurrence 50-20/1987-2 Page 2

5. Conditions Prior to Occurrence:

The reactor was on analog control at s steady-stacc power of 4.71 MWt with the shim bank at 10.30 inches. Channel #7, the linear flux channel, was indicating 86.0 pa. The eactor had been operating at power for only a few hours and xenoc was build-ing into the core. The regulating rod was therefore ceing gradu-ally withdrawn by the analog automatic controller . fu order to Gompensate for the negative reactivity associated wilb the xenon.

When the regolating rod attained a height of abcut 11.30 inches,

- the console operator decided to reshim the reactor.

6. Desegiption of Occurrence:

Reactor reshims are normally performed by first placing the

, nactor on manual control and t. hen ins e r t.ing the regulating rod while maintaining the reactor power to within 1.5% of the desired power level. Each of the reactor's six shim blades are then withdrawn slightly so as to (1) maintain the power within the ope ra t.ing band and (2) maintain an even shim bank height'. The -

pro:ess is continued until the . regulating rod is inserted to

. maut 2.50 inches.

Relative to the reshim in question, the operator placed ' the

' r reactor on manual control and selected the first shim blade (blade #1) with the shim blade selector switch. He then d e two mistakes. First, he turned the pistol-gnp handle of the regu-lating rod's control switch so that the rod moved outward instead of inward. This action had only a smali ef feet on the react or power because the regulating rod's differential reactivity worth at 11.30 inches is relatively low. However, it did cause the neutronic power to exceed the allowed deviation band. Operation i in this manner is contrary to existing written proceduro. The operator's second mistake was more serious. Rather thau fuvestigating the reason for the power deviation being on the positive side of the allowed operating band and co nt ra ry t.o :he normal practice of not withdrawing a blade unless the power is on th' i m side of the band, he began withdrawing the' blade. As a result, the neutronic power rose rapidly. The linear flux channel attained a value of 94.6 pa which corresponds to a powe.'

level of 5.18 MW. Upon reaching that, pwer level, the reactor 's safety system caused an automatic shutdawn on excessive power.

7. Descripti3n of Apparent Cause of Occurrence:

The apparent cause of this occurrence was operator error in that O) the operator moved the regulating rod in the wrong direction cad (2) withdrew a shim blade while the power level exceeded the desired value.

8. Analysis of_0ccurrence:

The reactor's neutronic power, as measured by the trace recorded on the strip chart f or channel #7 (the linear flux chan-

Reportable Occurrence 50-20/1987-2 Page 3 3

nel)[ reached ' 5.18 W. It exceeded the license limit of 5.0 W f or 2no'saore than 2 or 3 secco.ds. A copy of the relevant portion

- of ' thin strip chart is attached.

Reactor power, as recorded on ]

the dierO1 power strip chart, .did not change f rom its original value of 4.71 W.

It in. not expected inat an excursion to the 5.18 W neutron-ic power le vel reached in this case, which is well below the i authorized limiting eafety system setting of 6 W, would in any j way cause any damage to the reacto r. Nevertheless, immediately following this occurrence, analyses we re made of the primary coolant. No abnormalities were identified. The core purge gas monitor os normal and ' a subsequent visual inspection of the reactor ese revealed no abnormalities. l'hese actions confirmed that no damage occurred to the reactor.

9. Correctf.ve Action:

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The 'following corrective actions have been taken:

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(a) The operator involved in this occurrence was suspended from f

, all 1(ceused duties pending further review of the circum-

, stances anii a decision regarding appropriate retraining and/

or disciplinary measures.

(b) This occurtence was re41cwed by the senior reactor staff and by the Chairman of the MIT Reactor Safeguards Committee on f 1

'4 , 13 November 1987.  ;

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(c) The reactor staff reviewed the existing written procedures governing the performance of reshims and determined them to  ;

be adequate.

(d) This occurrence was discussed with . all licensed operators I

and the importance of properly performing reshims was emphasized. l a

10. Failure Data:

l No evend of this exact type has previously occarred. An ]

/ improper reshim did gecur ' on 19 November 1985 but it did not i l .

result in a reportable c event and its causes were very dif ferent

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, f rom those described in this report.

Sincerely,

/s u

'wan S. Kuok s ohn A. Fernard, Ph.D. Lincoln Clark, Jr. ,

. Asst. Superintendent Superintendent Director of Operations l 1

JAB /gw ,

Oopy to: MITRSC USNRC, Region I - Chief, Reactor Projects Section IB USNRC, Region 1 - Project Inspector USNRC - Resident Inspector, Pilgrim Nuclear Station

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Reportable Occurrence 50-20/1957-2

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