Simulation of Molten Salt Electrorefining Process of U-Pu-Zr Ternary Alloy

The integrated closed-cycle fast reactor nuclear energy system is an important measure to accelerate the implementation of the “three-step” strategy of nuclear energy. Electrorefining dry reprocessing technology is suitable for the treatment of fast reactor spent fuel with high burn-up consumption, high plutonium content, strong radioactivity, etc., which is a key link and practical technology choice for fast reactor spent fuel reprocessing. The fast reactor closed fuel cycle not only improves the utilization rate of uranium resources, but also reduces the radioactive activity of minor actinides, which is the only way for the sustainable development of nuclear energy. Dry reprocessing is a key part of the fast reactor closed fuel cycle, which is a realistic technology choice for fast reactor spent fuel reprocessing. Molten salt electrorefining dry reprocessing technology is a pyroprocessing technology with sufficient research and high technical maturity. In the process of research on the electrorefining process of spent fuel, the experimental research is very expensive and time-consuming, the experimental conditions and variables cannot be carried out comprehensively, and it is difficult to obtain reliable data under extreme conditions. The electrochemical changes of high-temperature molten salt electrorefining process can be explored through computer simulation, which can reduce the investment of experimental time and capital cost in the research process of electrorefining. Based on the electrochemical theory and backward difference method, a model of the electrorefining process of U-Pu-Zr ternary alloy was established, the dissolution and deposition behavior of each element near the electrode was simulated, and the changes of electrode potential, partial current and material distribution of each element under different mass transfer coefficients and uranium ion concentration in the initial molten salt were analyzed. The results show that the mass transfer coefficient affects the current distribution between the elements in the process of anode uranium-plutonium co-dissolution and cathode uranium-zirconium co-deposition, and increasing the mass transfer coefficient can improve the separation efficiency reduce the power loss. When the uranium ion mass fraction in the initial molten salt is as low as 0.073%, the cathode potential is lower than the apparent potential of plutonium after 45 minutes of electrorefining, and the plutonium begins to be co-deposited with uranium at the solid cathode, and the deposition of the two elements is competitive. Therefore, in the process of electrorefining, enhanced mass transfer technology can be considered; at the same time, in order to avoid the deposition of Pu, it is necessary to reasonably control the uranium ion concentration in the initial molten salt.