Control and surveillance of redox potential for Pa dissolution in 2LiF-BeF molten salt.

Pa, the precursor nuclide of U in the thorium-uranium conversion is prone to reductive deposition in 2LiF-BeF (66 : 34 mol%, FLiBe) molten salt. We explored the adjustment and control of the redox potential of the FLiBe melt to avoid the Pa reduction deposition. The experimental data indicated that the deposited Pa can be completely dissolved and reentered into the molten salt with the addition of oxidant NiF, and the distribution and behaviour of uranium, thorium, neptunium, and most fission products did not have any significant change in the NiF-oxidised FLiBe molten salt, showing the feasibility of this manner to make Pa exist stably in the melt. The effects of NiF-addition on the behaviour of the fission products Nb and I in the FLiBe molten salt were also investigated. It was found that I could be used as a redox indicator to monitor the redox potential of the oxidation-enhanced FLiBe molten salt. All the information drawn from this study could provide significant support for the control and surveillance of the redox potential of the FLiBe molten salt in the upcoming thorium molten salt reactor (TMSR).