Fabrication and thermophysical property characterization of UN/U₃Si₂ composite fuel forms

High uranium density composite fuels composed of UN and U₃Si₂ have been fabricated using a liquid phase sintering route at temperatures between 1873 K and 1973 K and spanning compositions of 10 vol% to 40 vol% U₃Si₂. Microstructural analysis and phase characterization revealed the formation of an U-Si-N phase of unknown structure. Microcracking was observed in the U-Si portion of the composite microstructure that likely originates from the mismatched coefficient of thermal expansion between the UN and U₃Si₂ leading to stresses on heating and cooling of the composite. Thermal expansion coefficient, thermal diffusivity, and thermal conductivity were characterized for each of the compositions as a function of temperature to 1673 K. Hysteresis is observed in the thermal diffusivity for the 20 vol% through 40 vol% specimens between room temperature and 1273 K, which is attributed to the microcracking in the U-Si phase. Thermal conductivity of the composites was modeled using the MOOSE framework based on the collected microstructure data. The impact of irradiation on thermal conductivity was also simulated for this class of composite materials.