Electrochemical Behavior Of Cerium In LiCl-KCl System And Thermodynamic Separation Of Cerium And Uranium

In recent years,molten salt electrolysis technology has been widely used,especially in the dry post-treatment technology of spent fuel.The nature of the elements in molten salts and liquid metals determines the separation processes’selectivity between these two phases.This information is essential for creating a promising version of the future nuclear fuel cycle using pyrochemical reprocessing of spent nuclear fuel in molten salt media.Therefore,it plays an essential role in the post-treatment of thermochemical pyrometallurgical nuclear waste.The thermochemical post-treatment technology represents a promising alternative to the aqueous process of separating actinides from irradiated fuels by applying electrolysis to molten salt media.In this process,the actinides are separated from most fission product elements by transferring electrons to the solid or liquid cathode.This thesis mainly carried out the following necessary work.In this thesis,a specific YZME electrode was used to study the interaction between oxygen ions and cerium ions in the molten 3Li Cl-2KCl eutectic in the temperature range of 723-823 K by potentiometric titration.It is determined that cerium can exist in the electrolyte in a stable state under soluble and insoluble conditions.The stable state of cerium compounds in the Ce-O system and the interaction mechanism of Ce³⁺and O^2-ions are established.The solubility constants of cerium oxychloride and oxide at different temperatures were determined.The primary thermodynamic data of Ce OCl and Ce₂O₃ are calculated.Pourbaix(E-p O^2-)diagram was drawn through the relationship between potential and oxygen ion concentration,and the characteristics of stable cerium species in the melt were summarized.This paper used cyclic voltammetry,square wave voltammetry,and open-circuit chronopotential methods to study the electrochemical behavior of cerium on liquid metal indium the 3Li Cl-2KCl-Ce Cl₃ melt on the inert electrode Mo and liquid metal In electrodes.On the redox process.The reaction kinetics of the oxidation-reduction process in the 3Li Cl-2KCl-Ce Cl₃ system is studied.The relationship between the diffusion coefficient,half spike potential,half-wave potential,and equilibrium potential of Ce³⁺on liquid metal In electrodes at different temperatures was determined.The expression of the diffusion coefficient and temperature of Ce³⁺on the liquid metal In electrode is:_1/2=-2.221-1.26×10^-4.The expression of the half spike potential and temperature of Ce³⁺reduced to Ce-In alloy on liquid metal indium electrode is:_1/2=-2.221-1.26×10^-4.The mechanism of the reduction process of Ce³⁺on the liquid metal indium electrode was determined.The electrochemical behavior of uranium and cerium on solid inert molybdenum and liquid active indium electrodes in a molten 3Li Cl-2KCl eutectic system with a temperature range of 723-823 K under inert gas flow was studied by the open-circuit chronopotentiometry method.Ce³⁺/Ce(U⁴⁺/U)couples’apparent electrode potential and apparent standard potential of Ce-In（U-In）alloys were established.The principal thermodynamic properties,activity,and solubility of cerium and uranium were determined.The separation factor of uranium/cerium couple in liquid indium electrode was calculated.The experimental results have shown a high value of separation factor,which decreases with increasing the temperature due to the entropy factor.