The efficient separation of used nuclear fuel into its relative components remains a critical challenge in the operation of a closed nuclear fuel cycle. Many solvent extraction processes have been either successfully applied or proposed to accomplish this separation. However, most of these processes necessitate several different discrete processes to fully partition fuel, which introduces challenges for industrial implementation. To reduce the cost and complexity of the separations, the concept of combining an acidic and solvating extractant into one solvent has become the focus of a large amount of research. Initial studies have shown that these processes hold great promise in their ability to partition used nuclear fuel. However, the fundamental chemistry controlling these processes is not well understood. Adducts are known to form between the extractants in the organic phase and evidence of mixed complexes forming between metals and the extractants has been reported. Investigations into these problems have been complicated by the structures of the multifunctional extractants used. To better understand the underlying chemistry of mixed extractant systems, we have proposed a new combination of extractants, Cyanex-923 and HEH[EHP], each monofunctional  organophosphorus extractants. By using simple solvating and cation exchanging extractants the fundamental chemistry that will define the performance of this combination is simpler to elucidate. The combination of these extractants has been investigated by solvent extraction, variable temperature NMR, FT-IR, UV-Vis, and time resolved fluorescence spectroscopy. The work presented here is the results of this study. It is hoped that these findings can be applied to other systems to better understand the nature of mixed extractant systems. This work was conducted atWashingtonStateUniversitywith support from the U.S. Department of Energy Fuel Cycle Research and Development Program, Sigma Team for Minor Actinide Separations.

Partitioning of used nuclear fuel using mixed extractants: A fundamental approach

247th National Meeting (2014)

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