Effects of intermetallic compounds on the thermophysical properties of uranium –palladium alloys

Abstract The formation and migration of high-yield lanthanide fission products during reactor operation and fuel reprocessing stages continues to be a critical area of concern for evaluating the performance of metallic fast-reactor nuclear fuels, particularly the formation of lanthanide-Fe eutectic compounds at the fuel-clad interface. Palladium has been shown to be an effective fuel additive for reducing fuel-clad chemical interaction (FCCI) by binding up lanthanide fission products and preventing their interaction with cladding materials, yet very little data exists for thermodynamic and thermal transport properties of actinide-palladium alloys. To better understand the effect of U–Pd intermetallic compounds on the thermophysical properties of metallic uranium, the phase transition temperatures (Ttr) and enthalpies (ΔHtr), specific heat capacities (Cp), thermal diffusivities (D), and the densities (ρ) as a function of temperature were experimentally measured or calculated for a series of alloys in the U–Pd binary system in a temperature range from 300 to 1173 K. These values were used to calculate the thermal conductivity (k) as a function of temperature for each composition and are reported in this paper. The addition of Pd led to an increased weight fraction of UPd3 as well as a substantial reduction in both D and ρ, and a small decrease in Cp at most temperatures measured. Consequently, the addition of 5 and 10 wt % Pd to U lead to a net decrease in k values of 23 and 40%, respectively, across the entire temperature range.