Research Progress of Nuclide Migration in Geological Disposal of High-level Radioactive Wastes

With the rapid development of nuclear energy, the nuclear technology has been widely used in various fields, such as industry, agriculture and medicine. However, the development of the nuclear industry also produces a large amount of radioactive waste, especially high-level radioactive waste (HLW), which has a quantity of nuclides with high radioactivity, high toxicity, long half-life and high heat generation. How to realize the long-term safe isolation of HLW from the environment is an important issue in global environmental protection. If it is not safely disposed, it will cause serious damage to the natural environment and human society. Therefore, the safe disposal of HLW is a key and difficult issue in nuclear waste management, and has been widely concerned by the international community. The deep geological disposal is generally considered to be the most effective and feasible method for disposing HLW. The main idea of deep geological disposal is to establish a geological disposal repository of HLW at a depth of 500-1 000 m underground where the processed HLWs are buried, and isolate HLWs from the biosphere through a multiple barrier system. The study of radioactive nuclide migration in geological barriers is one of the key topics for safety evaluation of deep geological disposal of HLW. In this paper, firstly the geological disposal of HLW and the study of radioactive nuclide migration were summarized, and then the key technologies of numerical simulation (the physical and mathematical models) for radioactive nuclide migration were discussed. Finally, the application progress of numerical simulation for migration of different radionuclides was analyzed. At present, there are the following main issues to be addressed in the study of radioactive nuclear migration: 1) The mechanism and law of nuclear migration are not completely clear, requiring more basic research and data support; 2) The experimental technology and equipment of nuclear migration need to be improved, requiring higher accuracy and sensitivity; 3) The numerical simulation of nuclear migration still has uncertainty and error, which needs more effective verification and optimization. The future research directions mainly include: 1) strengthening the theoretical study of nuclide migration and revealing the migration behavior and its control mechanism under complex conditions; 2) developing the experimental technology of nuclide migration and improving the quality and credibility of experimental data; 3) innovating the numerical simulation method of nuclide migration and enhancing the adaptability and prediction ability of the model; 4) improving the safety evaluation system of nuclide migration and establishing more reasonable evaluation indicators and methods.