Control and surveillance of redox potential for ²³³Pa dissolution in 2LiF-BeF₂ molten salt

²³³Pa, the precursor nuclide of ²³³U in the thorium-uranium conversion is prone to reductive deposition in 2LiF-BeF₂ (66 : 34 mol%, FLiBe) molten salt. We explored the adjustment and control of the redox potential of the FLiBe melt to avoid the ²³³Pa reduction deposition. The experimental data indicated that the deposited ²³³Pa can be completely dissolved and reentered into the molten salt with the addition of oxidant NiF₂, and the distribution and behaviour of uranium, thorium, neptunium, and most fission products did not have any significant change in the NiF₂-oxidised FLiBe molten salt, showing the feasibility of this manner to make ²³³Pa exist stably in the melt. The effects of NiF₂-addition on the behaviour of the fission products ⁹⁵Nb and ¹³¹I in the FLiBe molten salt were also investigated. It was found that ¹³¹I 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).