To enhance the extraction of remaining fissile nuclides from spent nuclear fuel through pyrochemical reprocessing, the operational lifetime of such fuels can be extended, ultimately leading to increased cost efficiency and a reduction in the amount of radioactively contaminated waste generated by fast-neutron reactors. Understanding the electrochemical behavior of fissile nuclides in LiCl–KCl is pivotal to the success of molten salt electrorefining pyrochemical reprocessing. In this pursuit, a comprehensive study of Pu(III) salt was conducted to comprehend its electrochemical characteristics within molten chloride salt mixtures. To achieve this, PuCl 3 was meticulously prepared by reacting PuO 2 with HCl in a LiCl–KCl mixture. Subsequently, we investigated the reduction mechanism, the diffusion coefficient of Pu(III) ( D Pu(III) ), and the apparent standard reduction potential of Pu(III)/Pu(0) ( E 0* Pu(III)/Pu(0) ) in situ, using a Mo working cathode. Our findings revealed that Pu(III) undergoes a single-step reduction to Pu(0), involving the exchange of three electrons. Furthermore, the rate of diffusion governs the reduction of Pu(III) at the Mo cathode. The relationship between the diffusion coefficient and temperature was described by ln D = − 5.51 to 4244.2/ T , with an activation energy of 35.28 kJ/mol. Additionally, we examined the temperature-dependent variations of E 0* Pu(III)/Pu(0) and the Gibbs free energy of formation for PuCl 3 (Δ G PuCl3 ). These dependencies were found to be E 0* Pu(III)/Pu(0) = − 3.194 + 6.4 × 10 −4 T and Δ G PuCl3 = − 924.5 + 0.185 T , respectively.

The ammonium ions produced by the reactions of relatively excessive dimethylhydroxylamine(DMHAN) with Fe3+, Ce4+ and Pu4+ in dilute nitric acid solutions at room temperature were determined by ion chromatographic method. The results show that the reactions between DMHAN and Fe3+, Ce4+ and Pu4+ all produce a certain amount of ammonium ramifications under acidic conditions, which includes (CH3)2NH+2, NH+4 and CH3NH+3. The reaction mechanism is as follows. When DMHAN reacts with Fe3+, Ce4+ and Pu4+ respectively, it can be oxidized and reduced simultaneously in the acidic solution for the -1 valence of N atom in DMHAN. Then part of DMHAN is reduced to (CH3)2NH+2, and it is further converted into NH+4 and CH3NH+3 partly. With the increase of redox potential of Fe3+, Pu4+ and Ce4+, the conversion ratio of DMHAN into amine ions increases and the proportion of (CH3)2NH+2 in total amine ions decreases, while the proportion of NH+4 in total amine ions increases.

In the last twenty years, direct electro-reduction of solid oxides in molten salt has been investigated extensively. Compared with thermodynamics, kinetics of this solid-to-solid reaction is far less concerned. In this work, Butler-Volmer model was adapted for cyclic voltammetric study of this reaction. Film electrode with three kinds of geometry was proposed to obtain kinetic parameters from the current-overpotential equations. AgCl reduction in 0.5 M KCl–0.5 M NaNO 3 was chosen as a model system. The main predictions of planar electrode and cylindrical electrode (inward) were well demonstrated by the electrodes constructed in this work, and the characteristics of cylindrical electrode (outward) were revealed by experimental results from literature. With the obtained relations, kinetics of AgCl/Ag reaction was carefully examined. By in-situ formation of UO 2 film on a planar surface in LiCl-KCl-UO 2 Cl 2 , the charge transfer coefficient and exchange current density for UO 2 /U reaction were obtained as 0.19 and 20 mA cm −2 , respectively. With the model, electron transfer in an irreversible solid state reaction can now be quantitatively described.

In this study, UCl4 was prepared by the reaction of HCl gas with UO2 in the LiCl-KCl eutectic. Then, the electrochemical behavior of U4+ and U3+ on a Mo cathode was investigated by various electrochemical techniques. The reduction process of U4+ was regarded as two steps: U4+ + e = U3+; U3+ + 3e = U. Diffusion coefficients of U4+ and U3+, the apparent standard potential of U4+/U3+, U3+/U as well as U4+/U in the LiCl-KCl molten salt on the Mo electrode was determined by numerous electrochemical methods. The thermodynamic functions of formation of Gibbs free energy of UCl4 and UCl3 are calculated as well.

Considering the good solubility of 2,6-bis(5,6-di-n-propyl-1,2,4-triazin-3-yl)-pyridine(DPTP) and avoiding the third phase formation,octanol-dodecane(ODOD) with a volume fraction of 30% was selected as the diluent.The distribution ratios of Am(Ⅲ) and Eu(Ⅲ) were studied as a function of a number of parameters such as contact time,nitrate ion and the nitric acid concentration in aqueous phase,the concentration of DPTP in the organic phase.A counter-current cascade(10 mL glass tube with plug) extraction experiment was carried out with 0.04 mol/L DPTP/ODOD.In the experiments,the flow rate ratios are as following: F∶X∶S=1∶0.63∶0.25,BF∶BX =1∶1;the feed solution,Eu(Ⅲ)+Am(Ⅲ) in 1.0 mol/L HNO3 solution;scrubbing solution,1.0 mol/L HNO3 solution;stripping reagent,0.01 mol/L HNO3.The results show that the recovery of Am is 98.42%,only containing 0.1% Eu in the organic solvent,and the stripping efficiency of Am and Eu both are 99.9%,the separation factor of SFAm/Eu is 45,SFEu/Am is more than 103.