ML20214R329

Requests Exemption from Conversion of Reactor Fuel to Low Enriched U,Per Definition of Unique Purpose in Accordance W/ 10CFR50.64.Design Based on Use of High Enriched U & Programs Serve Us Natl Interest.Related Info Encl

ML20214R329
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	09/25/1986
From:	Lisa Clark MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20214R331	List: ML20214R329 ML20214R350 ML20214R381
References
NUDOCS 8609290143
Download: ML20214R329 (8)

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Vd NUCLEAR REACTOR LABORATORY AN INTERDEPARTMENTAL CENTER OF

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

Director (617)253 4202 o, rector of Reactor operations September 25, 1986 Mr. Harold R. Denton, Director Office of Nucicar Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

MIT Reactor, Determination of Unique Purpose License No. R-37, Docket No. 50-20

Dear Mr. Denton:

In accordance with 10 CFR 50.64, the Massachusetts Institute of Technology hereby submits its application for a determination by the l U.S. Nuclear Regulatory Commission that the MIT Research Reactor (MITR-II) has a unique purpose and, therefore, qualifies for exemption from conversion of its reactor fuel to low enriched uranium (LEU).

The application is based on the definition of unique purpose, i.e., "a project, program or commercial activity that cannot be reasonably accomplished without the use of IIEU (highly enriched uranium) fuel". All four of the examples included in the definition apply to the MIT Reactor. The more general examples, nos. 3 and 4, are addressed first "Research projects based on neutron flux levels...." and "A reactor core of special design that could not perform its intended function....".  !

l The intended function of the MIT Reactor core is to provide the neutrons required for the research and education programs in nuclear technology at the Institute. The student and faculty research pro-grams encompass neutron physics, nuclear materials research, trace element analysis for several disciplines, computer control of reactors, corrosion and dose reduction studies, nuclear medicine and many others. Most of these require the maximum thermal or tast neutron fluxes available in our high performance 5 MW reactor, and i

these are currently attainable only with IIEU fuel (unique purpose example no. 3). liigher fluxes would be very desirable if they could l be achieved. In fact, many of our research uses are limited by the available flux levels and would become increasingly difficult and non-competitive at reduced flux levels. Furthermore, the need for increased neutron fluxes in order to stay competitive with other facilities, including those abroad, requires consideration of future upgrades to increase flux levels significantly.

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I Mr. Harold R. Denton September 25, 1986 l

Other MIT use is for academic purposes in about 10 MIT courses each year. The student involvement in both research and course activities at the MITR-II provides valuable education and training for i young people who have of ten, af ter graduation, assumed leading roles

! in nuclear science and technology. In addition to utilization by MIT, the reactor is an important adjunct to the research and educational 1

activities of regional universities, hospitals and industrial firms.

l Descriptions of the MIT and non-MIT research and academic uses of the i reactor are provided in References 1 and 2. Highlights of MIT research are provided in Reference 3.

Detailed statistical data on the MIT use of the reactor are provided in References 1 and 2 and include the following significant information (fiscal year 1984-85):

4 Research Users:

MIT students, faculty, staff and collaborators 89 Non-MIT students, faculty and staff 34

! Academic Users:

MIT students 197 Non-MIT students 148 4 Visitors 876 i

< Publications:

MIT $2 Non-MIT 20 1

1 l It is our firm belief that the research and educational programs l supported by the MIT Reactor both for HIT and other institutions are i clearly in the U.S. national interest (unique purpose example no. 1).

The combination of a high performance reactor and a world-class j research-oriented university is also unique in the United States.

l The present need for llEU in the MITR-II core is the result of the 1 design objectives adopted in the late 1960's for ti.e modified reactor, i 1.e. maximum thermal neutron flux in the beam ports and maximum fast flux in-core, both of which require a compact core. THe design was based explicitly on the use of IIEU fuels (unique purpose example no. 2). Minimum core size was achieved by using IIEU at 1.4 g U/cc for the fuel meat in the initial cores, close to the highest uranium

, density available at the time. Economic considerations led to an l hexagonal core shape (approximating cylindrical geometry), which has

! 27 fuel positions. Several of these must be reserved for in-core i irradiation facilities (Figure 1). Control blades operate in slots

! built 1.to the six sides of the core housing, which in turn fits into i

l

1 Mr. Harold R. Denton September 25, 1986 1

a 20-inch diameter cylindrical cavity at the bottom of the primary j coolant tank in such a manner that coolant flows down through six narrow channels just outside the core to a small lower plenum and then back up through the fuel elements. The core is surrounded radially I and below by a heavy water reflector (Figure 2). Further details and

! illustrative figures are provided in Appendix 10.1 of Reference 1.

l In general, there are several approaches that can be considered in order to modify HEU cores to permit operation with reduced enrichment uranium:

a) Increase the uranium density in the fuel meat, core geometry and all dimensions remaining unchanged.

b) Enlarge the core by adding more fuel elements.

i I c) Increase the number of fuel plates per element, decreasing the coolant channel thickness correspondingly.

d) Increase the thickness of the fuel meat, decreasing the fuel j clad thickness and/or the channel thickness correspondingly.

The feasibility of reducing enrichment in the MITR by the means listed above is discussed in the following paragraphs.

i The simplest way in which to convert to LEU would be to increase the uranium content enough to compensate for the loss of enrichment, i without changing the geometry or any of the core dimensions. The

thermal-hydraulic performance of the rt5.ctor should then be unchanged. As mentioned above, the MITR-II was designed to use high i

density fuel meat; and, in recent years, the highest available uranium j density has been utilized, i.e. 1.6 g U/ce. Reducing the enrichment

from 93% to 20% would mean increasing the uranium density from 1.6 to I 7.4 g U/cc just to maintain the name amount of U-235 in the core and i to 8.6 g U/cc in order to add 15% or so more to compensate for the I poisoning etfeet of all the U-238 in the LEU.

Ef forts to increase the maximum achievable uranium density in fuel plates above the 1.6 g U/cc mentioned above were initiated by the Department of Energy in 1978 under its Reduced Enrichment Research and Test Reactor (RERTR) Program at Argonne National Laboratory. Full-scale tests have been successful with LEU elements loaded to 4.8 g U/ce, and a whole-core demonstration in the Oak Ridge Reactor is cur-l rently under way, using U 3Si 2~ Al fuel

• LEU mint P ates l with

loadings up to about 7 g U/cc (the most advanced LEU fuel currently l being considered) are being tested, using U Si,3 and the RERTR i Program anticipates qualification of such fuel by the end of 1989 (Ref. 4). It is apparent that suitable LEU fuel is neither currently j available nor under development. However, as will be seen below, it i may ultimately be possible to utilize the 7 g U/cc LEU in combination with other changes. Medium enriched uranium (MEU) is another I

I j Mr. Harold R. Denton September 25, 1986 I

j possibility, but such fuels likewise are not currently available, and j no schedule for their qualification has been established.

The second method, i.e., adding more fuel elements, is not fea-a sible for the MITR-II. There have been 24 or 25 elements in the core during normal 5 MW operation, leaving two or three positions for

, irradiation facilities. Please see Reference 5 and previous annual reports to USNRC. U-235 burnups in the neighborhood of 407,have been i achieved. Due to the compact core design, it is physically possible

{ to add only two or three more fuel elements to the core without a major rebuilding of the reactor on a scale comparable to the j $3,000,000 conversion of the MITR-I to MITR-II in the mid-1970's.

1 Enlarging the core by only two or three elements would be a negligible l contribution toward reducing the enrichment and could be made only by I sacrificing essential in-core irradiation facilities. Prospects for 1 future in-core irradiations (e.g., for PWR and BWR coolant corrosion j studies with the objective of reducing radiation exposure and for i j increased production of short-lived radiopharmaceuticals) indicate a j need for using more rather than fewer in-core facilities.

1 j The third method, i.e., increasing the number of fuel plates per j element, offers no opportunity to increase the total uranium content

of the core by the necessary factor of five or more, because the plate ,

i thickness is 0.080 inches compared to an already narrow channel thick-1 ness of 0.078 inches. Again, the compact HEU core design has already utilized most of the available space. ,

}

1 The fourth method consists of increasing the thickness of the  ;

I fuel meat and decreasing correspondingly the fuel clad thickness l

! and/or the channel thickness. The clad thickness is already at the '

j minimum feasible value (0.015 inches), and so the only remaining pos-j sibility is to consider a reduction in the coolant channel thickness.

j A preliminary study (Ref. 6) investigated the impact on the thermal-i hydraulic performance of the core resulting from increases in the fuel meat thickness using LEU with a corresponding decrease in the coolant channel. One criterion adopted required that, for the same fuel cycle l

j length, the reactivity at the end of the fuel cycle be the same with l LEU as with HEU. This permits lower initial core loadings than would j be the case if the reactivity at the beginning of the cycle with LEU were to be the same as with HEU (which would lead to a Innger cycle i with the LEU). As mentioned earlier, the MITR-II initially operated I with 445 g U-235/ element (1.4 g U/ce), but more recent fuel contains j 506-510 g U-235/ element (1.6 g U/cc). It is estimated in Reference 6 e that the MITR-II fuel meat thickness can safely be increased from O.030 to 0.035 inches and that LEU loadings of 538 g U-235, 6.7 g U/ce, will match the cycle length of the former 445 g U-235 HEU

elements, while 612 g U-235, 7.6 g U/ce, will be required to match the cycle length of the present 506 g U-235 HEU elements. Therefore, j in the future, when 6.7-7.6 g U/cc qualified fuel is available, it may

be possible to utilize LEU fuel in cycles comparable to present ones.

1

Mr. Harold R. Denton September 25, 1986 It must be emphasized, however, that our studies are still preliminary and that further in-depth analyses must be made to confirm them and to predict the neutronic and safety performances of the core.

Without attempting to analyze the comparative operating costs in detail, which would also require a knowledge of fabrication costs for the high density fuels, it is estimated that the fuel cycle costs for HEU fuels would, roughly, be inversely proportional to the fuel density. Hence, if the performance of LEU fuels is no better than today's HEU, costs can be expected to exceed those achievable with HEU fuels with similar total uranium densities.

In summary, the MIT Reactor design was based explicitly on the use of HEU fuels, the reactor programs significantly serve the U.S.

national interest, and the reactor requires HEU to achieve the necessary neutron flux levels and to perform its intended function.

MIT, therefore, requests a unique purpose exemption from the 10 CFR 50.64 requirement to convert from the use of HEU fuel.

Sincerely yours, C a-, UL { , ' .

Lincoln Clark, Jr.

LC/crh

Attachment:

Figures List of references

i 1 l

5 )

i List of Reference i

I l 1. The MIT Reactor Staff, " Report of Educational and Research Activities for Academic / Fiscal Year 1984-1985 with Selected Data from Previous Years", Report No. MITNRL-016 (January.1986).

1 (Enclosed.)

i

2. Clark, L., " Reactor Sharing Program Report for the Period September 1, 1984 - August 31, 1985", Report No. DOE /ER-10770-6.

{ (Enclosed.)

l

3. Harling, 0.K., and L. Clark, Jr., "MIT Response to USDOE Questionnaire on the Value of U.S. University Research and

Training Reactors", Report No. MITNRL-013 (April 1985).

} (Enclosed.)

4. " Reduced Enrichment for Research and Test Reactors", Proceedings 3 of an International Meeting, Petten, the Netherlands, Eds. P. von 1 der Hardt and A. Travelli (October 14-16, 1985).

l

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5. The MIT Reactor Staff, " Annual Report to the U.S. Nuclear l Regulatory Commission for the Period July 1,1985 - June 30, 1986" (August 1986).

6. Gehret, J.B. , Jr. , " Thermal Hydraulic Aspects of the Use of Low i Enrichment Uranium in the MIT Research Reactor", M.S. Thesis, Department of Nuclear Engineering, Massachusetts Institute of Technology (January 1984).

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