Phase-Dependent Properties of Irradiated Metallic Fuels

Metallic U-Zr and U-Pu-Zr fuels are being considered for use in fast reactors by Oklo's Aurora, TerraPower's Natrium, and Advanced Reactor Concept's (ARC) ARC-100. The licensing of these new reactors will require comprehensive knowledge of fuel performance and mechanistic fuel performance codes that accurately describe and predict fuel properties. The most prominent irradiation behaviors in metallic U-Zr and U-Pu-Zr fuels (e.g., constituent redistribution), that set them apart from other fuel forms, depend on key structural features (e.g., phases and porosity) and material properties (thermal and mechanical). Unfortunately, experimental data that captures phase-dependence of material properties is scarce, which prevents us from developing mechanistic physical property models for fuel performance codes. To fill this gap, we examine the microstructure and properties of metallic fuels irradiated in the Experimental Breeder Reactor-II. We will report on the phases and porosity formed within each constituent redistribution region and correlate the microstructure of the fuel with the fuel’s thermal and mechanical properties. We compare new findings to historical understanding of constituent redistribution and thermo-mechanical properties, and highlight how modern characterization approaches could help with the development of physics-based models for of these complex fuels.