INVESTIGATING THE SPECIATION AND EXTRACTION OF COMMERCIALLY IMPORTANT METALS FROM SPENT NUCLEAR FUEL RAFFINATES: AN INTEGRATED COMPUTATIONAL AND EXPERIMENTAL APPROACH
Samuels, Alex Christopher
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Understanding the solution chemistry of fission products in solution is central to the operation of the nuclear fuel cycle and to the environmental remediation of any byproducts that migrate away from waste disposal facilities. Actinides can be separated from fission products and can be reprocessed into mixed oxide fuel (MOX). The actinides also pose an hazard if released into the environment. Additionally other fission products, such as the platinum group metals, could potentially be extracted from spent fuel raffiniates and spent nuclear fuel (SNF) provide a new domestic feedstock for these commercially important metals. Actinides that leach from waste tanks can exist in various oxidation states in solution, thereby complicating the chemistry. Computational studies can supplement experimental work in this area and can help to create a holistic understanding of actinides in solution. A starting point for computational studies is to gain fundamental insight into their static geometries and electronic structure. In the past, several computational studies have examined different actinides in solution, but a systematic study of the actinide series, including various oxidation states, does not exist. In this study uranium, neptunium, and plutonium are examined in various oxidation states. The separation of rhodium (III) from other platinum group metals (PGM) continues to be relevant to modern separations chemistry, as natural deposits become depleted and SNF is being considered a potential feedstock. Rhodium, as well as other PGMs are produced by 235U fission, and in a commercial light water reactor around 4 kg of PGMs can be produced per ton of waste. This potential source could provide this much needed element used primarily in automotive catalytic converters for years to come. A combination of computational and experimental techniques have been applied to understand the aqueous behavior of selected fission products. Using computational calculations at the quantum mechanical level the hydration numbers of U, Pu, and Np in various oxidation states been determined. A combined approach was utilized to understand the speciation of Rh(III) in acidic media along with solvent exaction of Rh(III) from nitric acid was developed.