ML20154M650

RO 50-20/1988-1:on 880511,incipient Fuel Clad Defect Detected.Caused by Small Blister on One Element MIT-12 Fuel Plate.Element MIT-12 Removed from Core

ML20154M650
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	05/26/1988
From:	Bernard J, Lisa Clark, Kwok K MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE
To:	Office of Nuclear Reactor Regulation
References
50-20-1988-1, NUDOCS 8806020030
Download: ML20154M650 (4)

Text

..

9%- .

.=dA4 NUCLEAR REACTOR LABORATORY I - l

@ AN INTERDEPARTMENTAL CENTER OF MASSACHUSETTS INSTITUTE OF TECHNOLOGY

& w

%$ g #

O.K. HARLING 138 Albany Street Cambridge, Mass. 02139 L CLARK, JR.

Director Director of Reactor Operations (617)253 4211 May 26, 1988 Director of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Station PI-137 Washington, D.C. 20555 Subj ect : Reportable Occurrence 50-20/1988-1, Detection of an Incipient Fuel Element Failure Gentlemen:

Massachusetts Institute er ology hereby subnits this ten-day report cf an occurrence at the search Reactor in accordance with paragraph 7.13.2(d) of the Techas .1 Specifications. An initial re-port of this occurrence was made by telephone to Region I on May 12, 1988 to Mr. J. Kaucher. (Note: This report concerns the detection of an incipient fuel clad defect. Submission of this 10-day report was delayed relative to our telephone report because of the need to per-form additional tests to confirm our analysis.)

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

1. Report No: 50-20/1988-1 2a. Report Date: 26 May 1988 2b. Occurrence Date: 11 May 1988 (Problem Suspected) 16 May 1988 (Analysis Confirined)

3. Facility: MIT Nuclear Reactor Lat>ratory 138 Albany Street Cambridge, MA 02139

4. Identification of Occurrenc3:

A regularly scheduled refueling was conducted on 9-10 May 1988. This refueling entailed both the introduction of new fuel elements to the core and the rotation / inversion of partially spent elements in order to equalize fuel burnup. One of the ele-ments scheduled for inversion was number MIT-12 which had been in core position C10. Upon inverting element MIT-12 a dark spot was observed between two of the fuel plates. This spot was visible 8806020030 880526 PDR ADOCK 05000020 I

)

S DCD

! l l . 1 l <

! l 1 Reportable Occurrence 50-20/88-1 Page 2 when backlighted by the Cerenkov radiation. It was not viewable using normal lighting. (Note: Part of the standard MITR core inspection procedure is to observe all fuel channels using only l Cerenkov radiation as a source of illumination.) It was not possible to determine if the dark spot was a foreign obj ect l

lodged between the fuel plates or if it was an incipient clad defect. No abnormal activity had been detected in the reactor's core purge gas prior to the refueling. In an effort to identify the origin of the dark spot, water samples were drawn from the element using the MIT Reactor's standard "sipping" procedure.

These were then counted for activity. The activity in the sample from MIT-12 was above that of the controls, but still well within the range of normal statistical variation. It was then decided that the dark spot might be a foreign obj ect . Accordingly an effort was then made to dislodge it gently using a thin aluminum metal strip. This effort was unsuccessful. The refueling was then completed which included retaining element MIT-12 in core.

The reactor was taken to 100 kW for cne hour with the obj ective of generating sufficient short-lived fission product activity so that a clad defect would be detectable via the sipping process.

The fission product gas level in the reactor's core purge gas was monitored, as always, during this period. No abnormalities were observed. The reactor was then shut down and, after a thirty minute wait, both element MIT-12 and several control elements were again sipped. The iodine activity from element MIT-12 was approximately three times that of the controls. Element MIT-12 was then removed from the core. Further alpping analysis was performed on 16 May 1988. This confirmed the abnormal activity associated with element MIT-12.

5. Conditions Prior to Occurrence s Element MIT-12 was first inserted in the reactor's A-Ring on 18 January 1982. It then followed the standard MITR refueling l pattern of partial burnup in the A or B-Ring, transfer to tempo-rary storage ex-core, and then insertion in the C-Ring until fully depleted. MIT-12 was placed on the C-Ring on 2 February 1987 and remained thne continuously until the time of the occur-rence.

6. Description of the Occurrence:

No increase in the fission product gas level was observed either prior to or during this occurrence.

7. Description of Apparent Cause of Occurrence i The apparent cause of this occurrence is a small blister on one of element MIT-12's fuel plates. This blister is only visible when the element is in the inverted position and then only when backlighted with Cerenkov radiation.

Reportable Occurrence 50-20/88-1 Page 3

8. Analysis of Occurrence:

Quality assurance records on the manufacture of element MIT-12 do not indicate any deviations from the MITR specifications.

Element MIT-12 had been in-core while 69,449 INH of energy were produced. It has 343.77 grams of its original 506 gram loading of U-235 remaining. The point of peak burnup on MIT-12 was 71.51% of the allowed fission density (1.8 x 1088 fissions /cc).

The element as a whole had attained 32.1% of the limit. Primary coolant chemistry is carefully monitored. The three parameters measure (pH, chloride, conductivity) have generally been as specified. The few deviations that have occurred were too brief and of too low a magnitude ') have caused this occurrence.

9. Corrective Action:

The immediate corrective action consisted of removing ele-ment MIT-12 from the core. Fission product gas levels were normal prior to the occurrence and have remained normal. The clad failure was detected and addressed during its incipient stage.

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 and #50-20//9-4A dated 26 Novemer 1980. Excess outgassing occurred in an "MIT" seri.es element in September 1983, in July 1985, in February 1996 and in October 1986. Refer to ROR #50-20/83-2, #50-20/85-2, 50-20/86-1, and 50-20/86-2. The current failure is the least severe of those noted. ("MIT" series fuel was made by Atomics International. The "4M" series was made by Gulf Atomic.

Currently, fuel is being procured from Babcock and Wilcox.)

Operating experience with fuel from all manufacturers has been good, except as noted below. Of 43 elements made by Gulf Atomic, 42 elements (630 plates) have been permanently discharged from the core after peak burnup approached the license limit.

The other 4M series 91ement 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 the 36 elements made by AI and subsequently used in the MITR core, four elements (60 plates) have achieved the maximum permissible burnup and have peak fission densities of 1.58 x 1082 fissions /cc and average burnups of 37.4%. Twenty-seven other AI series elements (405 plates) new in use have peak fission densities in the range 0.07-1.53 x 1025 fissions /cc. As previously reported, four other AI series elements were previously discharged due to excess outgassing.

The failure of this fifth AI element means that five plates i from a total of 540 plate.s have now exhibited excessive out-

V -

Reportable Occurrence 50-20/88-1 Page 4 gassing. Because of the sensitivity of MITR-II monitoring equip-ment, radiction releases have been insignificant.

-Fuel for the MIT Research Reactor is currently being manu-factured by the Babcock and Wilcox (B&W) Company. Three elements (45 plates) have been in - core since 15 September 1987 ar.d have achieved peak fission d9nsities in the range of 0.12-0.14 1081 fissions /cc. Three other B&W elements were introduced during the .

refueling on 10 May 1988. I Sincerely,  !

Kwa b6 Kwok t-td . i Assistant Superintendent (k &

ohn A. Bernard, Ph.D Superintendent LA O "

Lincoln Clark, Jr.

Director of Operations JAB /CRH ect MITRSC USNRC, Region I - Chief, Rean, tor Projects Section IB USNRC, Region I - Project Inspector Reactor Projects Section IB USNRC, Resident Inspector Pilgrim Nuclear Station l

l l

l l

l l

l l

l I

_ - , . _ _ _ _ . . _ _ _ _ . . _ ,