b'Coordinated Examination ofUnderstanding the basic science principles governing thermal transport in metal Microstructure and Thermalfuel forms can enable new reactor designs.Properties of GammaT he focus of this research was to characterize the gamma phase of uranium-zirconium (U-Zr) alloy for thermal conductivity and Uranium-Zirconium Alloy inmicrostructure relationships. Material properties of the gamma phase VolumetricSpace are important to understand because the gamma phase is the dominant structure of the fuel during reactor operation. Thermal conductivity in metallic fuel systems during irradiation is affected by several factors, such as fission gas porosity formation, constituent redistribution and sodium infiltration into the periphery of the fuel. This investigation focused on the effect of constituent redistribution, mainly zirconium with temperature.TOTAL APPROVED AMOUNT:The gamma phase in this alloy system only exists above 600C. Data was collected $124,862 over 1 year from room temperature to above 600C to characterize the transition into the gamma PROJECT NUMBER:phase. Bulk and local thermal conductivity were measured on the sample test matrix 20A1052-027 with some success. One of the challenges to collecting local thermal conductivity at high temperature on the U-Zr alloy was that as the sample approached the gamma PRINCIPAL INVESTIGATOR:phase transition temperature, the surface properties changed. This is likely due to Cynthia Adkins the spinodal decomposition mechanism that occurs between the delta and gamma CO-INVESTIGATORS: phases of U-Zr. This scattered the thermal conductivity microscope laser signal and Andrea Jokisaari, INL made measurements very noisy and difficult to analyze. The spinodal decomposition Tiankai Yao, INL mechanism was examined on similar U-Zr samples using the heated transmission Zilong Hua, INL electron microscope stage and the results of that study aided the thermal conductivity data analysis.The thermal properties data collected on the gamma U-Zr system and its relationship to the microstructure are important because they inform the mechanistic understanding of the zirconium contributions in that alloy system. Therefore, these data are being incorporated into thermal transport models for irradiated metallic fuel by the Nuclear Energy Advanced Modeling and Simulation program.Thermal diffusivity versus temperature for all alloy compositions in this study measured by laser flash analysis. Slope changes above 500C indicate phase changes included on the U-Zr phase diagram.69'