Evaporation behavior of 2LiF-BeF₂-ZrF₄ molten salt with irradiated nuclear fuel

The evaporation behaviours of various components were investigated by using a low pressure distillation method in a 2LiF-BeF₂-ZrF₄ mixture containing irradiated ThF₄ and UF₄. The experiment showed that BeF₂ and ZrF₄ were found to mainly condensate at the outer cover, the coolest zone, and their relative volatilities vs. LiF were 9.8 and 32.2, respectively, while for ThF₄ and UF_4, at four different temperature zones the values were almost constant, at 0.1 and 0.3. The radioactivity of various nuclides was further detected using gamma spectrometer analysis. ¹³⁷Cs was hardly observed due to long half-time decay. ²³³Pa was found to co-evaporate with the carrier salt, while ²³⁹Np mainly remained in the residual salt as ²³⁷U. In different temperature zones, the decontamination factors of rare earth in receiver salts ranged from 10 to 10³. On the basis of the investigation, it was proposed that the distribution of various nuclides after distillation, may be helpful to design the feasible condensate system to recover the carried salt in a molten salt reactor.