Evaporation behavior of 233 Pa in FLiBeZr molten salt.

In thorium molten salt reactors (TMSR), 233 Pa is an important intermediate nuclide in the conversion chain of 232 Th to 233 U, 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 233 Pa in the FLiBeZr molten salt was investigated during a vacuum distillation process. The separation characteristics between 233 Pa 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 233 Pa 5+ evaporated more readily than 233 Pa 4+ and the other components of the fuel, the relatively low temperature and medium pressure were much more beneficial to the separation of 233 Pa 5+ from FLiBeZr salt in the evaporation process, with the maximum value of the separation factor achieving more than 10 2 . Results of distillation experiments also show that increasing the temperature and decreasing the ambient pressure enhances the separation between 233 Pa 5+ and most of the fission product nuclides due to the 233 Pa 5+ volatility more strongly depending on the process conditions. These results will be utilized to design a concept for a process for 233 Pa separation from the fuel of a molten salt reactor.