ML20081H819

RO 50-20/1983-2:on 830906,fission Product Gas Levels Rise from 2.8% Max Permissible Concentration in Jul 1983 to 4.57% in Aug Noted.Caused by Excessive Outgassing of Fuel Element MIT-08.Element Removed from Core

ML20081H819
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	09/15/1983
From:	Bernard J, Lisa Clark MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE
To:	Kinney W, Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
RO-50-20-1983-2, NUDOCS 8311070593
Download: ML20081H819 (4)

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

Dir:ctor (617)253- 4 21 1 Directorof Reactoroperations Sep tember 15, 1983 Dr. Thomas E. Murley, Acting Administrator Region I U.S. Nuclear Regulatory Commission Attn: Mr. W. Kinney, Reactor Inspector 631 Park Avenue King of Prussia, PA 19406 Subject : Reportable Occurrence 50-20/1983-2, 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 Sept. 7, 1983.

The format of this report is based on Regulatory Guide 1.16, Revision 1.

1. Report No: 50-20/1983-2 2a. Report Date: 15 Sept. 1983 2b. Occurrence Date : 6 Sept. 1983

3. Facility: MIT Nuclear Research Reactor 138 Albany Street Cambridge, Massachusetts 02139

4. Identification of Occurrence:

A steady increase in the fission product gas release over a period of several weeks to approximately 5% of the maximum permissible concentration (MPC) was interpreted as an indication of a possible fuel element cladding failure. It was decided that the best means to investigate this possibility was to both " sip" and visually inspect fuel elements during scheduled shut-downs. 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 dif fuses through the aluminum cladding or a blister. The 8311070593 0 #

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Dr. Thomas E. Murley September 15, 1983 Page 2 reactor was then operated at low power, approximately 1 Kw, for several hours for training while the water samples were being anelyzed. MIT-08 was identi-fled as having an abnormally high rate of outgassing. The reactor was then shutdown and preparations for refueling initiated.

5. Conditions Prior to Occurrence:

Element MIT-08 was first inserted in the reactor's B-Ring on 23 Feb.

1981. It remained in-core continuously until 18 Jan. 1982 when it was removed and placed in the fuel storage ring for subsequent reuse. This pattern is standard and has been followed for almost all of the MITR fuel elements . Element MIT-08 was placed in-core again on 27 June 1983. A slow, but steady increase in fission product gas levels was observed several weeks later.

6. Description of Occurrence:

The fission product gas levels obtained in accordance with standard sampling procedures rose from approximately 2.8% of MPC in July 1983 to approximately 4.57% one month later. In addition, spiking of the core purge monitor by a factor of about 1.5 for about one minute following reactor startups for the three preceding weeks was observed.

7. Description of Apparent Cause of Occurrence:

The apparent cause of this occurrence is excessive outgassing of fuel element MIT-08. Visual examinations of the element (under water) have been performed. What may be a blister is barely visible. It is located on the third plate of the element, counting plates radially outward from the core center. It appears to be about 0.5 inch in diameter, appears to invade the coolant channel by only a small amount, is only on one side of the plate, and is about 5"-6" from the top of the element. The exact mode of failure can not be determined without the use of hot cells and special facilities not available at MIT.

8. Analysis of Occurrence:

Quality assurance records on the manufacture of element MIT-08 do not indicate any deviations from the MITR element specifications. The forma-tion of the blister probably occurred in July-Aug. 1983. Element MIT-08 had been in-core while 22,600 MWH of energy were produced. It has 447 grams of its original 506 gram loading of U-235 remaining. It is standard MITR policy to both rotate and invert fuel elements in order to maximize b urnup . Neither of these operaitns had been performed on MIT-08 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

Dr. Thomas E. Murley September 15, 1983 Page 3 burnup on MIT-08 was 32.7% of the allowed fission density (1.810 fissions /cc),

the area where the blister occurred was in the low power region and only at 17.7% 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 pro-cedures 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-08 from the core. Fission product gas levels subsequently decreased and are currently only slightly up (3.3% MPC) over what was measured prior to the occurrence. All other in-core "MIT" series elements have been " sipped" and no abnormalities were found. MIT-08 was also again sipped at this time and the 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. The current failure was far less severe than that one. Also, it occurred in a "MIT", not a "4W',

series element. ("MIT" series fuel was made by Atomics International.

The "4M" series by Gulf Atomic.) The existence of a gradual and slight increase in the fission product levels in the NETR'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-08 was i not in the core during most of 1982 and there does not appear to be any l

connection between the possible problem described in the letter of 08/17/82 and this occurrence.

Operating experience with fuel from both manufacturers has been good, except as noted below. Of 43 elements made by Gulf Atomic, 26 elements (390 plates) have been permanently discharged from the core after peak burn-up approached the license limit. 16 other elements (290 plates) are still in use and have peak fission densities in the range 0.5-1.3 x 10 2t f/cc.

Average burnups in the above cases range from 14% to 35%. One failed in 1979 as reported earlier, at an average burnup of 32.5%.

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Dr. Thomas E. Murley September 15, 1983 Page 4 Of24elementsmadebyAIandnowinuse,greeelements (45 plates) have peak fission densities exceeding 1.37 x 10 f/cc, average burnup 33%.

21 other elements now in use (315 plates) have peak fission densities in 21 the range 0.1-0.5 x 10 f/cc.

On the basis of the above experience, the two failures are very likely fabrication defects and not generic problems.

Sincerely, M b John A. Bernard Superintendent y

{ -. -- 4$ { r-Lincoln Clark, Jr.

N Director of Operations JB/gw cc: MITRSC USNRC-0MIPC USNRC-DMB

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