Thermophysical properties of USi to 1673 K

Consideration of uranium silicide compounds as candidate nuclear reactor fuels requires the accurate knowledge of their thermophysical properties as a function of temperature. Stoichiometric USi has received little attention in the literature with regard to property characterization. This absence of data prevents modeling and simulation communities from predicting performance of uranium silicide fuels that are either nominally USi itself, or are designed with other uranium silicide phases but may include appreciable fractions of USi introduced as a result of the fuel synthesis or fabrication process. This study was undertaken to quantify the thermal expansion coefficient, specific heat capacity, thermal diffusivity, and thermal conductivity of USi from ambient conditions to just below the peritectic decomposition of the compound. Stoichiometric samples that were prepared by arc melting and powder metallurgical routes for thermophysical property measurements exhibited 94% USi phase, with the balance being U₃Si₅ phase that likely formed during the solidification process. An energetic phase transformation was observed at 723 K, which is attributed to the inclusion of the secondary U₃Si₅ phase.