As the world is moving away from traditional fossil-fuel-based energy sources, nuclear power emerges as a promising alternative due to recent advancements in small modular reactors (SMRs) that afford numerous energetic, economic, and environmental benefits. The increase in SMRs technology leads towards a demand for better separations and reprocessing of spent nuclear fuel. Current reprocessing efforts, such as PUREX process, rely on dissolution of solid nuclear fuel in concentrated acids with numerous subsequent solvent extractions, that require sophisticated infrastructure and strict process control. Such approach not only generates large volumes of caustic radioactive liquid waste that is expensive to dispose, but also is not economically viable as we are moving to modular nuclear power. Green alternatives to wet reprocessing could include mechanochemical methods, which have been underexplored within actinide chemistry as a tool to enhance chemical reactivity for reprocessing. Herein, we explore the mechanochemistry of solid uranium dioxide U(IV)O<sub>2 </sub>and uranium trioxide U(VI)O<sub>3</sub> with the range of alkali/alkali-earth metal peroxides to probe the chemistry of uranium in the solid state. We utilized single-crystal X-ray diffraction, powder X-ray diffraction, Raman and IR spectroscopy, as well as, SEM imaging to characterize the resulting product. Mechanochemical grinding of uranium oxides with metal peroxides results in the formation of uranyl triperoxide phases and induces the formation of superoxide anion, which in turn, captures carbon under ambient conditions resulting in alkali metal/uranyl carbonate phases. As a result, mechanochemistry is a solvent-free pathway toward water soluble uranyl peroxide and carbonate phases offering a green alternative to traditional acid digestion of spent nuclear fuels.

Mechanochemical synthesis of uranyl peroxides: Implications for nuclear fuel reprocessing

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