In nuclear waste management, processing of high-fissile-content spent fuel material requires special care to avoid nuclear criticality issues. This is done by adding neutron poisons, such as iron or manganese. Gadolinium, a lanthanide used as a burnable absorber in nuclear reactors and fuels, is a particularly good neutron poison. Gd is a rare earth element (REE) typically found in ores and other materials at parts per million concentrations. Recent efforts to identify feasible domestic altenative supplies have REE have focused on coal fly ash. One potential strategy is the extraction of REE from coal fly ash using solutions of organic acids in supercritical carbon dioxide. Batch reactions have shown promising results in terms of yields and REE selectively. A hurdle for scale up to continuous operation is the separation of the spent fly ash from the supercritical fluid while maintaining supercritical conditions. The fine particle sizes of the coal fly ash make most regulat filtration methods ineffective.
In this study, the design of cyclone separators was undertaken to take advantage of the particle density differences between the ashes and the supercritical fluids. To date, little research has been done on the use of supercritical carbon dioxide as the carrier phase in cyclones, warranting investigation on the impacts of unique supercritical fluid properties, compared to liquids or gases, on cyclone separator performance. Starting from hydrocyclone design assumptions, a computational fluid dynamics approach using ANSYS CFD software is being undertaken to help characterize particle and fluid behavior of the supercritical system before fabrication. The information of expected particle and fluid behavior will then be used to design and evaluate options for cyclone prototypes.
Keywords (limited): separations, nuclear, supercritical fluids
