Thomas Newton

MITR is a 6 MW research reactor that is currently operating using aluminide (UAlx) dispersion fuel that is 93 percent enriched in uranium-235. Its primary mission is research, although it is also used for student train­ing, particularly for nuclear engineers. The research performed at MITR focuses primarily on fast neutron experiments, including irradiation testing of cladding for next-generation light-water reactors and advanced nuclear fuel experiments.

The reactor core is highly compact and has a hexagonal geometry with 27 fuel assembly positions. Twenty-four of these positions contain fuel; the remaining three positions are reserved for experiments (see Figure 3-3). The

d N21-R6 (final design)

FIGURE 3-2 Planned future core map for the UWNR reactor. Fuel elements are shown in red, beryllium reflector elements are shown in grey, and white boxes are empty positions. SOURCE: Austin (2010).

aluminum-clad fuel plates (15 per assembly) are designed with longitudinal fins to increase the heat transfer area (see Figure 3-4). The thermal and fast neutron fluxes in the core region are approximately 3 x 1013 and 1 x 1014 neutrons per square centimeter per second (n/cm2-s), respectively. The core is light-water cooled and moderated, with six control blades located around the periphery.

MITR has not yet been converted to LEU fuel because an appropriate fuel has not yet completed development and qualification. In fact, MITR’s unique fuel assembly design and highly compact core complicate conver­sion. Currently available LEU fuels were judged not to be appropriate for use in MITR because they would not allow criticality to be maintained and would also require a complete redesign of the core. However, the use of high-density UMo monolithic LEU fuel (discussed in Chapter 2) is likely to allow conversion of the reactor core to LEU. It is the reference fuel used in the conversion analyses. This fuel is 19.75 percent enriched in uranium-235 and has a density of 15.5 grams of uranium per cubic centimeter (gU/cm3).