b'Modeling andUnderstanding the fundamental irradiation-induced microstructure Characterization of Alpha- and property changes of alpha-uranium enables metallic fuel research and development and basic energy science.uranium to Accelerate Metallic Fuels Development T his project focused on the investigation of irradiation-induced microstructure and property changes in alpha-uranium via a combination of modeling and experimental techniques. Alpha-uranium is the low temperature phase of uranium and is present in certain metallic fuel alloys. The heyday of alpha-uranium research was in the 1960s, prior to the invention and widespread availability of many modern materials science techniques. As a result, a fundamental understanding of the physics governing the irradiation response PROJECT NUMBER:of alpha-uranium is lacking. Due to the strongly anisotropic nature of alpha-20A44-121 uranium, which is driven by its orthorhombic crystal structure, an understanding of the behavior cannot simply be projected from other metals with similar TOTAL APPROVED AMOUNT:physical properties. The project elucidated basic physical properties to understand $1,755,109 over 3 years fundamental aspects of irradiation behavior of alpha-uranium. The focus was PRINCIPAL INVESTIGATOR:primarily on the behavior of point defects, their transformation to extended defects, Andrea Jokisaari and the effect of interfaces on irradiation tolerance and other mechanical behaviors and properties. This helped build basic science capabilities for irradiation research CO-INVESTIGATORS: and aid physics-based fuel performance models development. A combination Cheng Sun, INLof experiment and atomistic and mesoscale modeling were used in this work. Michael Benson, INL This research greatly expanded the knowledge of the fundamental properties of Xiang Liu, INL alpha-uranium, shed light on factors controlling the complex irradiation response Benjamin Beeler, North Carolina State Universityof the material, provided information useful to thermomechanical processing of the material, and developed a new in situ furnace for the Neutron Radiography Reactor at INL. These results add to the basic science capability of INL and improve the ability to fabricate and model certain metallic fuels. This project also improved integration between modeling, experimental, and engineering capabilities at INL and strengthened collaboration between INL and North Carolina State University.Conceptual illustration of the multi-scale mechanistic approach to studying the behavior of alpha-uranium. Left) The path of a diffusing interstitial at 550 K simulated with molecular dynamics. Middle) A measure of the sink strength of a grain boundary for vacancies and interstitials simulated with molecular dynamics. Right) The spatially-dependent elastic energy density in a polycrystalline alpha-uranium sample. 24'