Irradiation behavior of intermetallic uranium compounds used as fuel for research and test reactors

The majority of research and test reactors around the world employ aluminum fuel element designs that contain dispersed powders of uranium compounds as fuel. Specifically, two compounds are used, the uranium oxide U3O8 and an uranium aluminide mixed phase composed of the intermetallic compounds UAl2, UAl3, and UAl4, all made with highly enriched uranium (HEU), i.e., 93% 235U. The reduction of 235U enrichment to below 20%, to so-called low enriched uranium (LEU), required the use of higher density fuels for those applications where simply increased fuel loading was not feasible. Fuel-dispersant loading is in practice limited to ∼ 45 vol%. Fuel development in the Reduced Enrichment Research and Test Reactor Program has focused on uranium silicides (U3Si and U3Si2) as the most promising high-density fuels. The compounds U6Fe and U6Mn as well as U3Si containing some aluminum or copper were tested in search of stable high-density fuel. Some properties of the traditional and newly tested fuels are shown. All fuels were tested in the Oak Ridge Research Reactor in the form of miniature fuel plates. The irradiation performance capability of fuel plates is determined by the extent of plate thickness increases caused by fuel/aluminum interaction and irradiation-induced swelling of the fuel. The fuel swelling obtained with immersion density measurements is shown