b'Figure 1. Thermal conductivity as a function of radial location for fresh U-10 wt% Zr. Bulk thermal conductivity from LFA (dashed line), local TCM conductivity (solid circles), and local thermal conductivity calculated from TCM diffusivity (open circles) are comparedused in conjunction with other dataalso examined to identify the phases leading to a metallic fuel qualificationand porosity of the U-10 wt% Zr and approved safety analysis for use alloy brought on by temperature in the advanced reactor designs beingand neutron flux and correlate it proposed by Department of Energywith the thermal conductivity. and TerraPower. Bulk thermal properties including thermal diffusivity were measured Accomplishments:of a fresh sample of MFF-3 U-10 This study provides meso-scalewt% Zr by traditional measurement (20-100 m) experimental observa-tions of phase dependent thermaltechniques (i.e., laser flash analysis conductivity of Na-bonded legacy(LFA)). Local thermal diffusivity FFTF MFF-3 fresh and irradiatedwas measured using a thermal U-10 wt% Zr fuel (12 at% burnup).conductivity microscope (TCM) The calculated effective thermaldesigned around the thermoreflec-conductivity is compared to thetance measurement technique. This bulk measurements to validate themeasurement is capable of the meso-model assumption. The pre- andscale data collection of thermal post-irradiated microstructure wasdiffusivity and conductivity directly 2022|AFC ACCOMPLISHMENTS 123'