Molecular Dynamics Simulations Of Metal Electrode/molten LiCl-KCl-UCl₃ Mixtures Interface

Before fusion technology matures,fast reactors and pyroprocessing technologies that can quickly process spent fuel from fast reactors are important goals for the sustainable development of nuclear in China.Among many pyroprocessing technologies,molten salt electrolytic refining technology has been tested on a project scale,and it is a research hotspot in spent fuel pyroprocessing.The molten salts electrolysis mainly occurs at the Li Cl-KCl-UCl₃molten salts/electrode interface.Therefore,it is necessary to understand the structural and dynamical properties of the electrode/electrolyte interface in order to deeply understand the dynamics of the electrode process.In this thesis,the interfacial structures and interfacial free energy of Li Cl-KCl-UCl₃ molten salts/metal electrode are systematically studied by molecular dynamics simulation.The interfacial structures,interfacial capacitances and dynamical properties at the interface of the Li Cl-KCl-UCl₃ molten salts/metal electrode were revealed from the atomic scale.The relationship between the shape of the differential capacitance curve and the interface structure was analyzed,and the distribution and dynamical behavior of U（III）at the interface were discussed emphatically,which provides microscopic insights for further research on the electrodeposition mechanism of interface uranium and the rate of its charge transfer.Meanwhile,in order to evaluate the application of the constant charge model and the constant potential model in the simulation of molten salts interface,Li Cl-KCl-UCl₃ molten salts interface was simulated by the two models respectively,and the interfacial microstructure and the dynamical properties of ions in the interface region obtained by the two models were systematically compared.In addition,the multi-step thermodynamical integration method was used to calculate the free energy of the interface of Li Cl-KCl-UCl₃ molten salts/U.The results show that the interfacial structures obtained by the constant charge method is basically the same as that obtained by the constant potential method,especially when the potential difference is low.The Li Cl-KCl-UCl₃ molten salts/metal electrode interface structure obtained by these two methods is an ordered layered structure composed of multiple layers of excess anions and excess cations,which cannot be described by the traditional electric double layer model.However,the shape of the differential capacitance curve obtained by the two methods is obviously different,that is,there is a significant difference between the two methods in describing the response of ion properties to the applied electrode potential,indicating that the constant charge model has low accuracy in describing the ion transport at the electrode interface.The electrode/molten salt interface plays an important role in the study of the kinetics of molten salts electrolysis.This work is a supplement to the basic data of the Li Cl-KCl-UCl₃molten salts/metal electrode interface,and lays a foundation for the further study of the interfacial charge transfer in molten salts electrolysis refining process.