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.