Measurement of thermal diffusivity of de

The high void space of nuclear fuels composed of homogeneous uranium metal microspheres may allow them to achieve ultra-high burnup by accommodating fuel swelling and reducing fuel/cladding interactions; however, the relatively low thermal conductivity of microsphere nuclear fuels may limit their application. This study aimed to support the development of microsphere nuclear fuels by designing a test apparatus to measure the apparent thermal diffusivity of a packed bed of depleted uranium microspheres filled with argon in the void spaces. The Crucible Heater Test Assembly (CHTA) was utilized to record radial temperature changes caused by an initial heat pulse from a central cartridge heater, enabling the calculation of apparent thermal diffusivity using thermocouple data. Results indicated that depleted uranium metal microspheres exhibit significantly lower thermal conductivity compared to solid uranium metal, with a value of 0.431 ± 0.0560 W/m-K at 500°C to 176°C, in contrast to approximately 32 W/m-K for bulk uranium. This low thermal conductivity, along with the rapid formation of an oxidation layer even in low oxygen environments, may pose challenges for the implementation of depleted uranium microspheres in fast reactor designs.