The design of accident tolerant fuels poses considerable challenges in terms of understanding and controlling chemical and physical phenomena in complex systems under extreme conditions, over length scales from the atomic to the macroscopic, and time scales from femtoseconds to years. A growing body of knowledge shows that changing fuel composition and structure on the nanoscale can increase resistance to radiation damage and facilitate higher burn-ups. Controlling growth mechanisms is a critical aspect of these efforts to synthesize ordered actinide materials. However, the building blocks of actinide materials often lack the directional bonding needed to promote the stereochemical orientations of atoms needed for growth. This work shows that new synthetic methodology can be invented by developing a conceptual framework that accounts for the role of the coordination chemistry on material growth mechanisms. Our work leverages recent studies from LANL and LBNL, which showed that ligand K-edge X-ray absorption spectroscopy provides a direct and quantitative probe of electronic structure and bonding in actinide molecules. These molecular-level insights provided a basis for efforts to control the volatility and decomposition chemistry of precursors used in materials synthesis. Our efforts to synthesize actinide nanoparticles began by conducting mechanistic studies of chemical and thermal decomposition using porous organic frameworks as inert templates. A comprehensive imaging and spectroscopic effort showed that the templates limited nanoparticle growth to 1-3 nm, which is similar to the pore size (3 nm). Nanoparticle composition was varied to include actinide dioxide or tetrafluoride (AnO2 or AnF4) phases by varying the precursor chemistry and decomposition conditions. This presentation will also discuss our preliminary efforts to show how controlling properties including particle size and composition in well-defined actinide materials can affect the outcome of chemical and physical processes relevant to the use and storage of advanced nuclear fuels.

Harnessing the principles of coordination chemistry to control the growth of actinide materials

253rd National Meeting (2017)

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