ML20214V900

Revised RO 50-20/1986-2:on 861008,elevated Levels of Fission Gases Discovered in Primary Containment.Cause Undetermined. Refueling Initiated & Element MIT-19 Removed.All in-core Elements Sipped.No Abnormalities Found

ML20214V900
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	10/17/1986
From:	Bernard J, Lisa Clark MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE
To:	Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML20214V898	List: ML20214V895 ML20214V900
References
50-20-1986-2, NUDOCS 8612100003
Download: ML20214V900 (5)

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MASSACHUSETTS INSTITUTE OF TECHNOLOGY O K. HARLING 138 Albany Street Cambridge, Mass. 02139 L. CLARK. JR Dir:ctor (617)253- 4211/4202 Director of Reactor Operations October 17, 1986

" REVISED" Dr. Thomas E. Murley, Administrator Region i U.S. Nuclear Regulatory Commission Attn: Mr. R. Sommers, Reactor Inspector 631 Park Avenue King of Prussia, PA 19406

Subject:

Reportable Occurrence 50-20/1986-2, License R-37 ,

Excess Outgassing from a Fuel Element Centlement Massachusetts Institute of Technology hereby submits the 10-day report of an occurrence at the MIT Research Reactor, in accordance with paragraph 7.13.2(d) of the Technical Specifications. An initial report of this occurrence was made by telephone to Region 1 on October 10, 1986.

The format of this report is based on Regulatory Guide 1.16, Revision I.

1. Report No: 50-20/1986-2 2a. Report Date: 17 October 1986 2b. Occurrence Date: 9 October 1986

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

4. Identification of Occurrence:

Slightly elevated levels of fission product gases in the air purge that is maintained across the surf ace of the primary cool-ant were observed at 2030 8 October 1986. A sample of the purge gas was then drawn and analyzed. The preliminary analysis indi-cated that fission product gas icvels were approximately 20%

higher than normal. (Note: The maximum fission gas level ob-served was approximately 6% of MPC. The normal background level 0612100003 DR 061027 -

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.. *a Dr. Thomas E. Murley Page 2 is currently 5% of MPC.) Power was then reduced in accordance with existing procedures. It was decided to keep the reactor operating but at the reduced power level in order to maintain enough activity so as to be detectable by the " sipping" process.

Further purge gas samples were drawn and analyzed on 9 October.

These confirmed the existence of a slight increase in the fission gas levels. The reactor was shutdown at 1030 on 9 October 1986.

All fuel elements were sipped on 10 October 1986. Element MIT-19 was identified as having an abnormally high rate of outgassing.

A refueling was then initiated and element MIT-19 was removed from the core. Reactor operation was resumed on 14 October in accordance with the normal operating schedule and fission product gas release levels were observed to be normal.

5. Condition Prior to Occurrences Element MIT-19 was first inserted in the reactor's B-Rir.g on 29 March 1982. It remained in-core continuously until 8 November 1982 when it was removed. It was again inserted in the B-Ring on 29 September 1986. With minor exceptions, the reactor was oper-ated on its normal schedule of 90-100 hours / week of full power operation during all periods in which element MIT-19 was in the core.

6. Description of the Occurrence The fission product gas levels obtained in accordance with standard sampling procedores rose f rom normal operating levels to about 6% of MPC. All increases were well below the permitted conceatrations (even without averaging over time).

7. Description of Apparent Cause of Occurrence The apparent cause of this occurrence is not known. Visual examination (through water) of element MIT-19 revealed no de-facts. This examination was repeated using Cerenkov radiation to backlight the fuel plates. Both tests were performed with the element in its normal orientation and with it inverted. No defects or blisters were observed. (Note Small defects on interior portions of the pintes would perhaps not be detectable. )

8. Analysis of Occurrencet Qual ity assurance records on the manufacture of element MIT-19 do not indicate any deviations from the MiTR element specifications. Element MIT-19 had been in-core while 13,860.31 MWil of energy were produced. It has 471.77 grams of its original 506 gram loading of U-235 remaining. The point of peak burnup on L

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I Dr. Thomas E. Murley Page 3 MIT-19 was 19.21% of the allowed fission density (1.8 x 10 21 fissions /cc). The element as a whole had only attained 6.76% of the limit. Primary coolant chemis try is carefully monitored.

The three parameters measured (pH, chloride, conductivity) have generally been as specified. The few deviations that have occurred were too brief and of too low a magnitude to have caused this occurrence.

Relative to effluent releases, the combination of standard sampling procedures and the existence of procedures for handling any abnormalities in the sampling results means that the problem was quickly diagnosed, identified, and corrected. No significant t

I release occurred.

9. Corrective Action The immediate corrective action consisted of removing ele-ment MIT-19 f rom the core. Fission product gas levels subsc-quently decreased and are currently what was measured prior to the occurrence. All other in-core elements have been " sipped" and no abnormalities were found.

f 10. Failure Data:

A cladding f ailure occurred to a "4M" series element in June 1979. Refer to ROR #50-20/79-4 dtd. 2 July 1979 and #50-20/79-4A dated 26 November 1980. Excess outgassing occcurred in an "MIT" l

series element in September 1983, in July 1985, and in February 1986. Refer to ROR #50-20/83-2, #50-20/85-2, and 50-20/86-1.

l The current failure was less severe than the one in 1979. ("MIT" series fuel was mada by Atomics International. The "4M" series by Gulf Atomic.) The existence of a gradual and a slight in-crease in the fission product levels in the MITR's primary cool-l l

ant was reported to Region I as a matter of information on 17 August 1982. One element, MIT-21, was identified as being sus-pect at that time. MIT-19 was in the core during that portion of 1982 in which the elevated fission product gas levels were detected, and there was subsequent evidence that it experienced excessive outgassing and may have contributed to the p roblem.

Accordingly, it is anticipated that ele ment MIT-21 may be re-i tested at some future date.

l Operating experience with fuel f rom both manuf acturers has been good, except as noted below. Of 43 elements made by Culf Atomic, 35 elements (525 pintes) have been permanently discharged from the core af ter peak burnup approached the license limit.

Seven other elements (105 pintes) are still in use. One failed in 1979 as reported earlier, at an average burnup of 32.5%.

Average burnups on the Gulf Atomic fuct are in the range 42-44%.

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Dr. Thoma3 E. Muricy Pegg 4 Of the 36 elements made by AI, three elements (45 plates) have achieved the maximum pergissible burnup and have peak fission densities of 1.58 x 10 fissions /cc and average burnups of 37.4%. Twenty-nine other AI series elements (435 plates) now g use have peak fission densities in the range 0.14-1. 25 x 10 fissions /cc. As previously reported, three other AI series elements were previously discharged due to excess outgassing.

The f ailure of this fourth AI element means that four plates from a total of 540 plates have now exhibited excessive outgas-sing. Because of the sensitivity of MITR-II monitoring equip-ment, radiation releases have been insignificant. The loss of four elements at relatively low burnup levels, however, does represent a significant economic penalty. For other reasons, a new fuel f abricator is now producing MITR-II fuel.

Sincerely,

(/ k k John A. Bernard, Ph.D Superintendent Lincoln Clark, Jr.

Director of Operations

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