ML20214H954
| ML20214H954 | |
| 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) |
| References | |
| 50-020-86-02, 50-20-86-2, NUDOCS 8612010101 | |
| Download: ML20214H954 (4) | |
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' NUCLEAR REACTOR LABORATORY AN INTERDEPARTMENTAL CENTER OF fy/
MASSACHUSETTS INSTITUTE OF TECHNOLOGY l
O.K. HARUNG
'38 Albany Street Cambridge, Mass. 02139 L. CLARK JR.
Director (617)253-4211/4202 Director of Rea: tor Operations October 17, 1986 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 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 cccurrence was made by telephone to Region I 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 118 Albany Street Lambridge, MA 02139 4.
Identification of Occurrence:
Slightly elevated levels of fission product gases in the air purge that is maintained across the surface 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 levels were approximately 20%
higher than normal.
(Note: The maximum fission gas level ob-served was approximately 6% of MPC.
The normal background level ggs.s-C612010101 861017 PDR ADOCK 05000020
/g S
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 a*. 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 f rom 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 Occurrence:
Element MIT-19 was first inserted in the reactor's B-Ring on 29 March 1982.
It remained in core continuously until 8 November 1982 when it wts 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 operacicn 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 sampl ing procedures rose from normal operating levels to about 6% of MPC.
All increases were well below the permitted concentrations (even without averaging over time).
7.
Description of Appar t Cause of Occurrence:
The apparent cause of this occurrence is not known.
Visual examination (through water) of element MIT-19 revealed no de-fects. This examination was repeated using Cerenkov radiation to backlight the fuel plates.
Both tests we re performed with the element in its normal oric,tation and with it inverted.
No defects or blisters were o
-rved.
(Note:
Small defects on interior portions of the plat would perhaps not be detectable. )
8.
Anal rsis of Occurrence:
Quality 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 MWH 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
Dr. Thomas E. Murley Page 3 MIT-19 was 19.21% of the allowed fission density (1.8 10 fissions /cc). The element as a whole had only attained 6.76% of che 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.
l 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 ele-ment MIT-19 from the core.
Fission product gas levels subse-quently decreased and are currently what was measured prior to j
the occurrence.
All other in-core elements have been " sipped" and no abnormalities were found.
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
I 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.
The current failure was less severe than the one in 1979.
("MIT" series fuel was made by Atomics International.
The "4M" series by Gul f Atomic.)
The existence of a gradual and a slight in-crease in the fission product levels in the MITR's primary cool-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 e xpe r' 'nced excessive outgassing and may have contributed to the p ro blem.
Accordingly, it is anticipated that element MIT-21 may be re-tested at some future date.
Operating experience with fuel from both manuf acturers has been good, except as noted below.
Of 43 elements made by Gulf Atomic, (35 elements, 525 plates) have been permanently discharg-ed f rom the core af ter peak burnup approached the license limit.
Seven other elements (105 plates) are 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%.
s,.
9 L
Dr. Thomas 5. Murley l
Page'3 MIT-19'.was. 19.21% of the allowed fission der:sity (1.8 10 '
~
fissions /cc). The element as a whole had.only attained 6.76% 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 wa's quickly diagnosed, identified, and corrected.
No significant f
release occurred.
9.
Corrective Action:
The immediate corrective action ~ consisted of removing ele-ment MIT-19 from the co re.
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.'
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" series element in September 1983, in July 1985, and _ in February.
-- 1986.'
Refer to ROR #50-20/83-2,' #50-20/35-2, and 50-20/86-1.
The current failure was less severe than the one in 1979.
("MIT"
' series - fuel was made 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-ant was reported to Region I as a matter of information on 17 August 1982.
One element, MIT-21, was ident.ified 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 problem.
Accordingly, it is anticipated that element MIT-21 may be re-tested at some future date.
Operating experience with fuel from both manuf acturers has been good, except as noted below.
Of 43 elements made by Gulf
-Atomic, (35 elements, 525 plates) have been permanently discharg-ed from the core af ter peak burnup approached the license limit.
Seven other elements (105 plates) are stin 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%.
f
Dr. Thomas E. Murlsy
~
]
.Paga 4 Of the 36 elements made by AI. three elements (45 plates) have achieved the maximum permissible burnup and have peak fission densities of 1.58 x 20 f /ce, average burnup. 37.4%.
Twenty-nine other AI series elements. (435 plates) now.in use have peak fis-sion densities in tt e range 0.14-1.25 x 10 f/cc.
As previously reported, three other AI series elements were previously dis-charged due to excess offgassing.
The failure 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 fabricator is now producing MITR-II fuel.
Since rely, cNT John A. Bernard, Ph.D Superintendent M
Lincoln Clark, Jr.
Director of Operations JAB /gw cc: MITRSC USNRC-OMIPC USNRC-DMB
._