The burning of fossil fuels has been the primary source of energy for modern civilization. However, recently, the negative environmental impacts from these processes including the emission of pollutants and greenhouse gases, which accelerate climate change, have garnered much attention. This has necessitated the development of green, renewable energy, with one of the few energy sources that can be scaled to meet the growing demand being nuclear power. To enable the expansion of nuclear power several challenges need to be addressed. One of the main challenges is developing a separation/recycling scheme for used nuclear fuel (UNF) that enhances the recovery of the U, Pu, and other actinide (An) species. Sequentially, the ideal separation process should minimize the impact of waste bound for a geological repository, maintain the nonproliferation standards, and have the ability to scale the process for a diverse fleet of reactor fuels.
The aim of this research explores a single-step separation technology for the recovery of the actinides ranging from U-Am as a group, utilizing a co-crystallization with uranyl nitrate hexahydrate (UNH). Recent studies have shown the transuranic (TRU) species in their hexavalent state, Np(VI), Pu(VI), or Am(VI), which exist as the dioxo actinyl molecular ion, AnO₂²⁺, have near proportional removal from solution to that of U(VI). The co-crystallization approach has extremely high selectivity for the An(VI) species, while completely discriminating against fission products. Aspects of the separation of the hexavalent actinides from fission products will be discussed, at the 1-g and 10-g of U(VI) scales with special attention on the problematic fission product species like Mo, Tc, and Ru. These experiments will be analyzed by UV-Vis and ICP-MS to determine the separation of each element. Samples for analysis will be taken from pre-crystallization, post-crystallization supernatant, and from a solution of the dissolved crystalline product.
Am(III) will be added to the system in order to explore the optimal conditions of oxidation to Am(VI) using sodium bismuthate (NaBiO₃). Am and the other TRUs need to be in the 6+ state for this technology to properly incorporate them into the crystal lattice formed for separation from the fission products. Variables such as concentration of nitric acid, uranium, and sodium bismuthate and temperature will be investigated. The transition from Am(III) to Am(VI) will be monitored by UV-Vis over time.

Dr. Luke Sadergaski

Oak Ridge National Laboratory

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