Effect of structural phase transitions on high temperature thermal conductivity of nuclear-grade uranium

Reliable experimental evaluation of thermal conductivity of nuclear-grade uranium over a wide temperature range from 298 K to 1273 K, encompassing both of its solid-state allotropic phase transformations has been carried out for the first time using thermal diffusivity and linear thermal expansion data. Temperature dependence of both diffusivity and expansivity showed abrupt break at both the phase transitions namely, orthorhombic (α-phase) to tetragonal (β-phase) at 948 K and tetragonal (β-phase) to cubic (γ-phase) at 1051 K. Thermal conductivity also increases abruptly upon uranium undergoing structural modification from ambient temperature orthorhombic phase to high temperature cubic phase. Observed differences in results obtained in present investigation from those reported in literature have been explained on the basis of non-metallic impurity contents and inherent structural anisotropy of uranium. It has been suggested that structural anisotropy, which strongly affects metal’s microstructure; also notably influences the heat transport properties. High temperature body centred cubic phase (BCC) of uranium shows very high heat conductivity (44 W/m.K at 1075 K), which affirms the advantage of cubic-phase uranium alloys as potential metallic nuclear fuel. Presented results will be highly useful for development of uranium-based metallic alloy fuels. •Thermophysical properties of nuclear-grade uranium have been evaluated over 298 K–1273 K.•Thermal diffusivity of uranium shows abrupt variation at phase transitions.•Thermal conductivity trend in cubic phase stability region of uranium has been delineated.•High temperature cubic phase of uranium shows highest thermal conductivity.•Both, impurities and structural anisotropy in uranium affects its thermal conductivity.