ML20137G366

RO 50-20/1985-2:on 850715,defect in Fuel Element Cladding Observed.Caused by High Rate of Outgassing from Fuel Element MIT-32.Defective Element Removed

ML20137G366
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	07/23/1985
From:	Bernard J, Lisa Clark NUCLEAR REACTOR LABORATORY
To:	Murley T, Sommers R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
RO-50-20-1985-2, NUDOCS 8508270279
Download: ML20137G366 (4)

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1. ,1, s 7 NUCLEAR REACTOR LABORATORY - k,g AN INTERDEPARTMENTAL CENTER OF  %$'Jg/

MASSACHUSETTS INSTITUTE OF TECHNOLOGY O K HARLING 138 Albany Street Cambridge, Mass. 02139 L. CLARK.JR.

DirOctor (617)253-42 11 Director of Reactor Operations July 23, 1985 Dr. Thomas E. Murley, Acting 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 50-20/1985-2, License R-37 Increase in Outgassing of a Fuel Element Gentlemen 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 I on July 16, 1985.

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

1. Report No: 50-20/1985-2 2a. Report Da te: 23 July 1985 2b. Occurrence Date: 15 July 1985

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

4. Identification of Occurrence:

A steady increase in the fission product gas release over a period of several hours to approximately 5% of the maximum permissible concentration (MPC) was interpreted as an indication of a possible defect in the cladding of a fuel element. This increase started at about 1000 12 July 1985. The reactor was shutdown for the weekend at 1800 12 July 1985 in accordance with the standard operating schedule. It was decided that the best means to investigate this increased outgassing was to both " sip" B508270279 850723 ADOCK 05000020

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Dr. Thomas E. Murley July 24, 1985 Page 2 and visually inspect fuel elements prior to the next scheduled startup. The sipping process consists of collecting and counting one liter coolant samples drawn through the fuel element. This procedure, coupled with visual inspection using alternately light and the Cerenkov radiation to illuminate the plates, would permit:

determination of whether or not any particular element had either a higher fission product gas release than what normally diffuses through the aluminum cladding or a blister. This was done on 15 July 1985 and element MIT-32 was identified as having an abnormally high rate of outgassing. A refueling was then initiated and element MIT-32 was removed from the core. Reactor operation was resumed later on 15 July and fission product gas >

release levels were observed to be normal.

5. Condition Prior to Occurrence Element MIT-32 was first inserted in the reactor's B-Ring on 30 Jan. 1984. It remained in-core continuously until 15 July 1985 when it was removed. The reactor was operated on its normal schedule of 90-100 hours / week of full-power operation during this period.

6. Description of the Occurrence The fission product gas levels obtained in accordance with i standard sampling procedures rose from normal levels to 5% of MPC I- over a period of eight hours starting at 1000 12 July 85. This rise was steady and was not accompanied by periodic spiking of I the core purge monitor.

j 7. Description of Apparent Cause of Occurrence:

The apparent cause of this occurrence is excessive outgassing of fuel element MIT-32. Visual examinations of the element (under water) have been performed. No defect or blister l

is readily apparent. One member of the staff reports that he can

' discern what may be a tiny blister corresponding to the location where strain gauge measurements were made on the fuel plates

! during the manufacturing process. (Such checks are part of the quality assurance requirements.) However, other members of the staff could not confirm this. The exact mode of failure can not l

be determined without the use of hot cells and special facilities not available at MIT.

l 8. Analysis of Occurrence:

i Quality assurance records on the manufacture of element MIT-32 do not indicate any deviations from the MITR element

Dr. Thomas E. Murley July 24, 1985 Page 3 specifications. Element MIT-32 had been in-core while 28,718 MWH of energy were produced. It has 433 grams of its original 506 gram Icading of U-235 remaining. It is standard MITR policy to both rotate and invert fuel elements in order to maximize Eburtup. Neither of these operations had been performed on MIT-32 because it was not yet sufficiently advanced in the fuel cycle.

Power production in the upper portions of the MIT Reactor is, by design, kept low through the use of fixed poison plates. As a result, while the point of peak burnup on MIT-32 was 39.2% of the allowed fission density (1.8 1021 fissions /ce), the element as a whole had culy attained 14.4% of the limit. Primary coolant chemistry 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 release occurred.

9. Corrective Action:

The immediate corrective action consisted of removing element MIT-32 from the core. Fission product gas levels subse-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. MIT-32 was again sipped on 22 July 1985 and the prior existence of an abnormally high fission product release rate was confirmed.

10. Failure Data:

A cladding failure occurred to a "4M" series element in June 1979. Refer to ROR #50-20/79-4 dated 2 July 1979. Excess out-gassing occurred in an "MIT" series element in Sept. 1983. Refer to ROR #50-20/83-2. The current failure was far less severe than the one in 1979 and less severe than the one in 1983. ("MIT" series fuel was made by Atomics International. The "4M" series by Culf Atomic.) The existence of a gradual and slight increase in the fission product levels in the MITR's primary coolant was reported to Region I as a matter of information on 17 Aug. 1982.

One element, MIT-21, was identified as being suspect at that time. MIT-32 was not in the core during 1982.

Dr. Thomas E. Murley July 24, 1985 Page 4 Operating experience with fuel from both manufacturers has been good, except as noted below. Of 43 elements made by Culf Atomic, 41 elements (615 plates) have been permanently discharged from the core af ter peak burnup approached the license limit.

One other element (15 plates) is still in use. One failed in 1979 as reported earlier, at an average burnup of 32.5%. Average burnups on the Gulf Atomic fuel are in the range 42-44%.

Of 33 elements made by AI and now in use, three elements (45 plates have peak fission densities exceeding 1.50 x 2021g/ce, average burnup 37%. 27 other elements now in use (405 lates) have peak fission densities in the range 0.1-0.75 x 10 2gffee, On the basis of the above experience, the failures are very likely fabrication defects and not generic problems.

Sincerely, fN &

John A. Bernard Superintendent (d [k '

Lincoln Clark, Jr.

Director of Operations JAB /gw cc MITRSC USNRC-0MIPC USNRC-DMB 1

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