Understanding the local thermal conductivity evolution of neutron irradiated U3Si2 dispersion fuel via state-of-the-art thermo-reflectance measurements

This study presents the first thermal conductivity measurements performed on neutron irradiated U3Si2 dispersion fuel cladded in an aluminum matrix (in a plate geometry). These were performed via a novel set-up which consists of a thermo-reflectance apparatus, known as the thermal conductivity microscope (TCM), deployed in a shielded glovebox. Thermal conductivity was measured across different fuel particles at various positions along the plate length and correlated to the local burnup. Back scattered electron images were collected at each position and analyzed to obtain estimates of the local porosity. It was shown that the thermal conductivity of the irradiated fuel particles is approximately 25% to 35% lower compared to the unirradiated material. A solid-state physics model was used to interpret the measured data. According to the model the degradation in thermal conductivity is consistent with the presence of insulating, fission gas filled pores or bubbles as well as loss of long-range order due to irradiation induced amorphization.