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

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 (T_tr) and enthalpies (ΔH_tr), specific heat capacities (C_p), 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 C_p 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.