Impact of composition on the thermophysical properties of (U,Zr)C solid solution Carbide fuels

The use of uranium-zirconium carbide solid solutions in nuclear thermal propulsion (NTP) is promising due to their advantageous material properties. However, due to uranium enrichment limitations, it is crucial to understand how increased uranium content affects these properties. This study investigates the impact of varying uranium content on the thermophysical properties of substoichiometric uranium-zirconium carbide solid solutions, represented as (UyZr1-y)C, where y = 0.05, 0.1, 0.2, and 0.3. These compositions were synthesized through carbothermic reduction and densified using direct current sintering. Our phase characterization and elemental analysis underscore the necessity of using carbon-substoichiometric feedstock powders to accommodate carbon diffusion during processing. We report on the density, specific heat, and thermal diffusivity of these compositions up to 1473 K, revealing consistent trends across the compositional range. Calculated thermal conductivities from these properties, when extrapolated to NTP-relevant temperatures, show a significant decrease with increasing uranium content. This finding has critical implications for NTP fuel technology and underscores the need for further high-temperature studies.