Thermal conductivity measurement of U-Mo and U-Mo/Al interaction layers generated from in-pile irradiation using the suspended-bridge method

This study presents the first measurements of the individual thermal conductivities of U-7 wt.%Mo fuel particles and U-Mo/Al interaction layers (ILs) from in-pile-irradiated dispersion fuel plates using the suspended-bridge method. Nanorods of U-7 wt.%Mo fuel and U-Mo/Al ILs were extracted by focused ion beam (FIB), and their microstructures were characterized with transmission electron microscopy (TEM). TEM revealed finely distributed nanobubbles in the U-7 wt.%Mo matrix, along with an amorphous structure in the ILs. The thermal conductivity of in-pile-irradiated U-7 wt.%Mo was approximately 30 % lower than that of the unirradiated material, ranging from 6.7 W/m·K at 300 K to 8.5 W/m·K at 380 K. The ILs exhibited even lower thermal conductivity, from 2.1 W/m·K at 300 K to 2.7 W/m·K at 380 K. These reductions, attributed to nanobubbles, fission products, and irradiation-induced point defects, were analyzed through a combination of microstructural characterization and literature-based transport models, which successfully reproduced the observed degradation trends.