Plutonium-uranium-zirconium (Pu-U-Zr) alloys have attracted attention for application in advanced fast reactors. Compatibility of the fuel with cladding is one of the most important factors that have to be considered prior to an alloy’s implementation in nuclear reactor environment. Interdiffusion between fuel and cladding is imperative for understanding of the useful lifetime of nuclear reactor components and fuels. The project aims to characterize complex phases formed upon heat treatment of diffusion couples constructed from Pu-U-Zr alloys and Fe cladding. Detailed chemical and structural characterization of interdiffusion between fuel and cladding the atomic scale is of profound consequence for evaluation of nuclear fuels and materials behavior. This proposal requests access to focused ion beam (FIB) and localized electrode atom probe (LEAP) instruments for thorough characterization of formed intermetallic phases. The proposed work will lead to enhancement of fundamental understanding of fuel performance and fuel-cladding chemical interactions.

Technical relevance of the proposal is directly related to the Department of Energy Office of Nuclear Energies mission to advance nuclear power as a resource capable of meeting the nation’s energy, environmental, and national security needs, and the mission to develop next-generation advanced nuclear fuels. The proposed project will benefit the Fuel Cycle Technology (FCT) program, funded by DOE NE and Advanced Fuel Cycle Initiative. Fuel swelling and resulting fission product transport to cladding is a limiting factor in lifetime and safety of thermal and fast reactor systems. Understanding diffusion kinetics and phases formed between metal fuel and cladding upon exposure to high temperatures typical in reactor environment is critical for ensuring integrity, safety, and performance of the material, advancement of this type of fuel in the future, and securing long-term success of the nuclear fleet. Limited literature exists on the phases formed in quaternary Fe-U-Pu-Zr systems, which is based on investigation of phase relations via differential thermal analysis and energy dispersive spectroscopy (EDS) in scanning electron microscopes (SEM). Detailed structural analysis and chemical composition analysis of formed complex phases is yet to be conducted. The proposed work will allow advanced detailed characterization of the fuel-cladding interaction product microstructure and chemical composition, which will ultimately lead to the development of improved nuclear fuel with enhanced performance.