Unirradiated characteristics of U-Si alloys as dispersed-phase fuels

To satisfy the power demands of many research reactors, a new low-enriched uranium fuel with a high density and uranium content was needed. Any fuel must be compatible with aluminum and its alloys so that it may be fabricated as a dispersed-phase in aluminum alloy and aluminum matrix plate-type elements following, as nearly as possible, established commercial manufacturing techniques. The U-Si and U-Si-Al alloys at or near the composition of U3Si were immediately attractive because of work documented by Canadian researchers. The paper illustrates the U-Si system. All intermediate phases, within the experimental ability to define them, are line compounds. For the goals of the Reduced Enrichment Research and Test Reactor Program, attention has focused on U3Si (3.9 wt% Si) and U3Si2 (7.3 wt% Si) and compositions between these limits. Densities and hardness for as-arc-cast and heat-treated ingots in this composition range are shown. Photomicrographs corresponding to these compositions and conditions have been published. Because of its higher uranium content and density, U3Si was the more attractive candidate fuel even though a prolonged heat treatment is required to complete the peritectoid reaction. The U3Si2 has a tightly bonded tetragonal structure with Si-Si bonds, whereas U3Si has a less tightly bonded crystal (cubic above 7650C, tetragonal below) with no Si-Si bonds. As others have noted, U3Si2 has performed better than U3Si in an irradiation environment