ML20235J062
| ML20235J062 | |
| Person / Time | |
|---|---|
| Site: | MIT Nuclear Research Reactor |
| Issue date: | 02/13/1989 |
| From: | Bernard J, Kwok K MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20235J065 | List: |
| References | |
| NUDOCS 8902240149 | |
| Download: ML20235J062 (4) | |
Text
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!g NUCLEAR REACTOR LABORATORY k
8' AN INTERDEPARTMENTAL CENTER OF h47/
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MASSACHUSETTS INSTITUTE OF TECHNOLOGY
. O.K. HARLING 138 Albany Street, Cambridge, Mass. 02139 J.A. BERNARD. JR.
Director '
Telefax No. (617)253 7300 Director of Reactor Operations Telex No. 92-1473 MIT CAM Tel. No. (617) 253-4202 February 13, 1989
- (
U.S. Nuclear Regulatory Commission l
Washington, D.C. 20555 l
l ATTN 2 Document Control Desk Subj ect: Amendment Request and SAR Revision No. 37, Facility License No. R-37, Docket 50-20 Gentlemen:
The Massachusetts Institute of Technology is writing this letter to the Commission for the purpos.e of requesting an a:aendment to the Facility Operating License which would be a revision in the technical specification governing the fission density limit.
Forwarded with j
this letter is the proposed wording of the specification change and i
the supporting safety analysis.
Also forwardea is Revision No. 37 to the MITR Safety Analysis Report which revises sections of the SAR con-cerning _ the fission density limit.
The safety evaluation and SAR revision have been approved by the MIT Reactor Safeguards Committee.
Please contact the undersigned (617)253-4211/4202 should you require any further information in this matter.
Sincerely, L'TL w k
Kwan S.
wok Superintendent C4 John A. Bernard, Ph.
Director of Reactor Operations JAB /crh
Enclosures:
Safety Review #0-88-13 SAR Revision No. 37 (Part of SR #0-88-13) cci MITRSC (with enclosures)
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_ Safety Review #0-88-13 i
Revision to !!ITR Technical Specification #3.11.2(e)
Concerning the Fission Density Limit and SAR Revision No. 37 1.
Backaround MITR fuel is intermetallic UA1.
In accordance x
with technical specification #3.11.2(e), the fission density limit for such fuel is 1.8 1088 fissions /cm8 if it contains 4 to 7% voids.
This limit was established more than a decade ago when the operating license for the MITR-II Research Reactor was r
issued.
This limit reflected the known state of the technology at that time.
However, it has subsequently been shown through extensive testing at the Advanced Test Reactor (ATR) that this limit is needlessly conservative.
Accordingly it is desired to revise this limit so that it is in keeping with the current state of the technology.
2.
Description of Change:
Technical specification #3.11.2(e) would be revised so that a
fission density limit of 2.3 1085 fissions /cm8 would be observed.
Also, the pecentage of voids permitted in the UA1x type fuel used for the MIT Research Reac-tor would be changed from
'4 to 7%' to
'4 to 11%'.
A final change is that the parenthetical note on p.
3-43 of the basis of Technical Specification #3.11 is deleted.
This note indicates that the fuel is approximately 35 weight-percent U-235.
The exact wording of the proposed change to the technical specifica-tion and its basis is given in Appendix A to this safety review.
3.
Benefits of the Proposed Change: The proposed change will permit increased flexibility in the management of fuel at the MIT Research Reactor.
This will in turn reduce the number of fuel elements in the cycle at any given time.
The expected advantages are therefore reduced fuel procurement costs and possibly less concern regarding security issues.
l-Utilization of fuel in both research and commercial reactors L
is of ten optimized by periodically shif ting the location of each element within the core so as to equalize the effects of flux gradients.
Relative to the MIT Research Reactor, elements may also be rotated in place and inverted.
The combination of these j-three practices (shift, rotation, inversion) has enabled the MITR Staff, through careful planning, to utilize 40-44% of the initial uranium loading in each element.
Currently, when an element has on the whole lost 40-44% of its initial loading, its mid-section will be approaching the fission density limit of 1.8 1085 fis-sion/cm.
Hence, the element must be discharged.
In general, 8
j the core of the MIT Research Reactor would also require refueling
}
at this time in order to maintain sufficient excess reactivity so as to allow operation.
Hence, there was no reason to raise the fission density limit even though, as shown in Section 4 of this f
review, the technical justification for so doing did exist.
This
(
situation has now changed and it is believed that future core configurations will permit the depletion of individual fuel ele-l SR #0-88-13 DEC 20 1988 l:
.U
...3' ments to more than 40-44%. of the initial loading while still maintaining sufficient. excess reactivity.
Hence, it is. now desired to raise the fission density. limit.
So doing will, as noted, eventually reduce the total number of fuel elements-in the MITR fuel cycle at any given time.
4.
Safety Evaluation:
The principal document supporting the safety of this proposed change is a referesd paper entitled, " Develop-ment and Irradiation Performance of Uranium Aluminide Fuels on Test Reactors" by J. M. Beeston, R. R. Hobbins, G. W. Gibson, and W. C. Francis. The paper appeared in the June 1980 issue of Nuc-lear-Technoloav and a copy is enclosed ' as Appendix B to this safety review.
In that paper, it is noted thats (a) The fission' density limit for UA1 x type' fuel in use at the 4
Advanced Test Reactor (ATR) is 2.3 1088 fissions /cm.
The I
8 ATR's operating environment is more severe than that of the l
MITR-II.
i (b) The irradiation performance of more than 1700 fuel' elements was observed during the ten year ATR program on the evalua-1 tion'of UA1x fuel.
l The information obtained from the ATR research program is direct-ly transferable to the MIT Research Reactor with the exception of l
the fact.that the ATR data was obtained at 373-473 K while the l
MITR-II operates at 330-350 K.
The question therefore arose as I
to whether or not the lower MITR temperature would have an ad-l verse affect on the allowable fission density limit.
This was discussed with EG&G Idaho (R.R. Hobbins) and it was concluded that the lower MITR-II temperature would either have no effect or a beneficial effect on the proposed change in the fission density limit. The following arguments were considered I
(i)
The generation of solids (i.e.,
two fission product atoms from one U8' fission) is the primary cause for burnup limitation.
The volume changes are accommodated by the free volume in the matrix and this process is temperature l
independent.
(ii)
Blistering of the clad is due to gases and is more likely to occur at higher temperatures.
The lower MITR tempera-I tures should produce a lesser tendency for blistering.
(iii) The fission product gases are well contained in sub-microscopic bubbles at the ATR temperatures, and cause i
little effect on burnup limitations.
The lower tempera-tures of MITR-II should not change this phenomenon appre-ciably and bubble migration and agglomeration would be slightly reduced.
(iv)
Buckling of the fuel plates was observed in ETR (Engineer-I ing Test Reactor) type fuel and was evaluated as a possi-ble limit for ATR (and hence MITR-II) type fuel.
Buckling SR #0-88-13 DEC 20 1988
t
. ".4
.s as a f ailure~ mode for ATR fuel plates was not. observed, probably because the plates are svaged to the edge pieces and yield more easily than the ETR pinned design.
The MITR-II fuel plates are roll-swaged similar to the ATR and thus buckling should not be a problem.
The ' percent voids permitted in the intermetallic UA1 type fuel x
used by.the MIT Research Reactor would be changed from '4 to.7%'
to ' '4 to 11%'.
Also the parenthetical note on p.
3-43 of the basis of Technical Specification #3.11 is deleted. This note in -
dicates that the' fuel is 35 weight-percent U-235.
These changes will allow the manufacturing variability that is permitted by the fuel f abrication specifications of other reactors that use this type of fuel.
Also, a figure. of 4 -to 11% voids is consistent with the data tabulated by Beeston et. al. (Table III, p. 141).
In summary, it is concluded that a fission density' limit of 2.3 1088 fissions /cm8 for MITR fuel is technically supported by the' extensive ATR research program and by subsequent ATR opera-ting experience.
5.
Security:. This proposed change will have no effect on the MITR Security Plan.
If anything, the MITR fuel will become slightly more self-protecting. However, MITR fuel is already so far above the self-protection criteria that this increase is not relevant.
6.
Handling of Spent Fuel:
Existing procedures and equipment will be retained for the handling of spent fuel.
The additional burn-up made possible by the change in the fission density limit will not significantly increase the radiation icvels associated with l
spent MITR fuel.
l 7.
Unreviewed' Safety Question Determination:
The proposed change f
does involve a technical specification but is judged not to i
constitute an. unreviewed safety question.
It should be noted i
that this change will not create a new type of accident.
No new mechanism of fuel element clad failure is introduced by. this j
change and no margin of safety is reduced. Also, the probability of an analyzed, existing accident such as clad blistering or its consequences is not increased.
Evidence for this last point is the ATR data.
8.
SAR Revision No.
37:
Appendix C to this report contains the proposed revision to the MITR Safety Analysis Report.
Relative to UA1x at 2.3 1088 fissions /ce, the following is noted:
a)
Swellina Beeston calculates swelling to be 2.6%F/1082 where F is the number of fissions /cc.
For F equal to 2.3 1083 fissions /ce, the swelling would be 6%.
This is below the 8.5% figure originally shown in the SAR to be acceptable, b)
BlisterinR Beeston's data. puts the blister temperature in excess of 700 K at 2.3 1088 fissions /ce.
Peak MITR-II fuel temperatures are about 330 K, well below the blister temperature.
SR #0-88-13 DEC 20 1988