Study On The Properties Of Main Lanthanides In Spent Fuel Molten Salt Electrorefining

With the large-scale development of nuclear power,the cumulative amount of spent fuel is also increasing,which brings potential hazards to the environment and nuclear safety.How to properly deal with the spent fuel is an inevitable problem for the long-term sound development of nuclear energy.China adheres to the route of a closed nuclear fuel cycle with fast reactors,treating and recycling spent fuel,which can not only ensure the long-term development of China’s nuclear energy and provide a steady flow of clean energy,but also minimize high-level waste that is potential hazards to the environment.A million-k Wh nuclear power plant produces about 25-30 tons of spent fuel annually.If calculated based on the China’s current installed capacity of 48.74 million kilowatts,the annual generated spent fuel will reach 1200-1400 tons.However,currently there is only one spent fuel reprocessing plant with an annual processing capacity of 50 tons in China,thus the processing capacity is seriously insufficient.It is urgent to develop new spent fuel reprocessing technology.Pyroproceessing is one of the most promising dry reprocessing technologies at present.It involves the molten salt resistant to strong radiation as an electrolyte and is very suitable for processing spent fuel with high burnup.In the pyroprocessing,molten salt electrorefining is the key step to realize the separation between actinides and lanthanides.However,due to the similar properties of actinides and lanthanides,the effective separation between them is difficult.Therefore,in order to improve the separation rate of lanthanum and actinide elements,and promote the engineering application of pyroprocessing,it is necessary to focus on research related to molten salt electrorefining.This article focuses on the current difficulties in molten salt electrorefining.The main research contents and results are:（1）The separation of actinides and lanthanides requires to grasp the properties of various spent fuel elements in LiCl-KCl molten salt.Kinetic simulation of electrode process of two typical lanthanides（CeCl₃ and NdCl₃）was developed based on the finite element method in LiCl-KCl molten salt.The electrode kinetic process simulation was carried out under a series of different concentration and temperature conditions.The electrode kinetic process simulation of the two-step reduction（NdCl₃）was solved by a stepwise calculation method.Most of the elements in spent fuel belong to single-step reduction or two-step reduction.Therefore,the simulation of CeCl₃ and NdCl₃ can cover the behavior of most spent fuel elements in the molten salt of LiCl-KCl,which provides technical support to obtain the properties of spent fuel elements in LiCl-KCl molten salt.（2）Aiming at the problem of mutual influence between the properties of multiple elements in the electrolytic separation of molten salt,we conducted a study on the law of mutual influence between the elements of the multi-solute molten salt system.The data of single solute（LaCl₃ or Gd Cl₃）in LiCl-KCl molten salt and mixed LaCl₃-Gd Cl₃ in LiCl-KCl molten salt were analyzed.The cyclic voltammetry curves with severe overlap were separated by the curve fitting technique based on genetic algorithm,which utilizesd the single solute curve as the base function,and a great separation performance is obtained.By comparing the separated curve with the single solute curve,the mutual influence law between the elements in the multi-element molten salt system was revealed,which can provide a theoretical basis for the design of the electrorefining process.（3）Aiming at the problem of low electrorefining efficiency in the process of electrolytic separation of molten salt,the electrochemical behavior of CeCl₃ in LiCl-KCl molten salt under the external magnetic field was carried out.Using cerium as the target element,whose properties are similar to uranium,to study the difficulty of low current efficiency in molten salt electrolysis.The effect of external magnetic field on the electrochemical behavior of molten salt was studied by finite element method.The results show that the external magnetic field has a flattening effect on the current of electrode surface,and it also affects the magnitude of the current.The application of an external magnetic field is expected to improve the current efficiency and separation efficiency of the molten salt electrolysis process.