Evaporation behavior of 2LiF-BeF 2 -ZrF 4 molten salt with irradiated nuclear fuel.

The evaporation behaviours of various components were investigated by using a low pressure distillation method in a 2LiF-BeF 2 -ZrF 4 mixture containing irradiated ThF 4 and UF 4 . The experiment showed that BeF 2 and ZrF 4 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 ThF 4 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. 137 Cs was hardly observed due to long half-time decay. 233 Pa was found to co-evaporate with the carrier salt, while 239 Np mainly remained in the residual salt as 237 U. In different temperature zones, the decontamination factors of rare earth in receiver salts ranged from 10 to 10 3 . 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.