Improving the economics of nuclear power in the United States will require advanced nuclear fuels that can achieve longer service lifetimes and enhance safety margins. Recent research has shown that fuels can be designed with nanometer-sized grains to increase radiation tolerance and impart fission gas retention and heat transfer capabilities. Further improvements in the performance of advanced nuclear fuels will require an ability to control the size and composition of actinide nanomaterials, and to understand the advantages and potential limitations of exploiting nanoscale chemistry in fuel designs. Harnessing this complex nanoscale chemistry will require access to a region of actinide synthetic space that is relatively unexplored and beyond current predictive capabilities. The primary objective of this work is to establish new methods to synthesize actinide nanoparticles (NPs) in a manner that provides control over size and composition. 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. Because the synthetic targets are complex, multi-component systems with hierarchical structure, a multi-pronged imaging and spectroscopic characterization strategy has been developed to ensure that definitive analyses are conducted on well-defined materials. For example, small-angle X-ray scattering, transmission electron microscopy, and ptychography are used to probe nanocrystal size, while oxygen K-edge and actinide L3-edge X-ray spectroscopies are used to determine composition. This presentation will discuss our synthetic and characterization efforts, as well as recent progress in evaluating 5f-electron behavior with changes in size and composition at the nanometer level.

5f-Electron behavior of actinide nanoparticles embedded in porous frameworks

2019 Spring National Meeting

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