Study on the condensation behavior of the key metal fluorides in molten salts during low-pressure distillation

Abstract

BackgroundIn thorium-based molten salt reactors (TMSRs), 233Pa is an important intermediate nuclide in the conversion chain of 232Th to 233U, and 233PaF5 can be effectively separated from carrier salt by low-pressure distillation. However, some of the metal fluoride is vaporized along with 233PaF5 simultaneously, and the evaporated fluoride may condense at different temperatures.PurposeThis study aims to investigate the condensation behavior of 233PaF5 and other key metal fluorides in the FLiBeZr molten salt during the low-pressure distillation process.MethodThe FLiBeZr molten salt containing PaF5 and various metal fluorides was low-pressure distillated to examine the condensation behavior of 233PaF5 and key metal fluorides at different temperatures. Then, the optimal temperature of key metal fluorides was evaluated and the separation characteristics between them and 233PaF5 were figured out. Finally, the separation factors of 233PaF5 and the other metal fluorides were calculated and compared with those of the entire low-pressure distillation process at the optimum condensation temperature of 233PaF5.ResultsThe results show that the optimal condensation temperature for 233PaF5 and 95NbF5 is within the range of 600~700 ℃, whilst it is within the range of 400~500 ℃ for 237UF4 and 95ZrF4. The comparison results show that there is no significant difference in the separation factors of 95NbF5 and 233PaF5, but the separation factors of 233UF4 and 95ZrF4 are increased by a factor of two to 20 times.ConclusionIt is confirmed that the separation coefficient is determined primarily by volatilization, but can be further improved by varying the condensation temperature.

Keywords

• low-pressure distillation
• flibezr
• condensation behavior
• 233paf5
• key metal fluorides