In thorium molten salt reactors (TMSR), 233Pa is an important intermediate nuclide in the conversion chain of 232Th to 233U, its timely separation from the fuel salt is critically important for both the thorium-uranium (Th-U) fuel cycle and the neutron economy of the reactor. In this study, the evaporation behavior of 233Pa in the FLiBeZr molten salt was investigated during a vacuum distillation process. The separation characteristics between 233Pa and the major components of the fuel (salt and fission products) were evaluated in a calculation of the separation factors between these components. It was found that 233Pa5+ evaporated more readily than 233Pa4+ and the other components of the fuel, the relatively low temperature and medium pressure were much more beneficial to the separation of 233Pa5+ from FLiBeZr salt in the evaporation process, with the maximum value of the separation factor achieving more than 102. Results of distillation experiments also show that increasing the temperature and decreasing the ambient pressure enhances the separation between 233Pa5+ and most of the fission product nuclides due to the 233Pa5+ volatility more strongly depending on the process conditions. These results will be utilized to design a concept for a process for 233Pa separation from the fuel of a molten salt reactor.
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