Optimization Research Of Coverage Materials For Uranium Tailings Pile Under Multi Field Coupling

Abstract:With the rapid development of China's nuclear power industry,a large number of uranium mines have been decommissioned or are to be retired.According to the surveys,the radon exhalation rates of most decommissioned uranium tailings piles in our country have exceeded the limited standards of the relevant laws and regulations,and the radioactive pollutant radon and its daughters have long-term and potential harm to the ecological environment and the health of people around the uranium tailings piles.Therefore,it is of great significance to the management of retired uranium tailings piles.Through the visual simulation of the spatial and temporal distribution of radon concentration and immune genetic algorithm analysis in the uranium tailings and coverage materials under multi field coupling,carrying out optimization research of uranium tailings'coverage materials,the study achieved the optimal selection of the covering materials.This has important theoretical and practical significance for the manegement of solid waste such as uranium mine contaminated sites.The research contents of this thesis are mainly presented in the following aspects:(1)According to the pollutant migration kinetics,fluid mechanics and heat transfer theory,combining with the pollutant migration and transformation mathematical model and the radionuclide radon migration mechanism,a radon transfer model for the finite thickness uranium tailings piles was established.The effects of porosity,diffusion coefficient,density,adsorption coefficient,dispersion coefficient and the radiative capacity of radon in medium on radon migration were studied;(2)Based on the constructed radon migration model of finite thickness uranium tailings piles,a radon transfer model of uranium tailings piles under deformation field,seepage field and temperature field is established,to further eatablish the radon transfer model in the covering materials under multi-field coupling so as to obtain the quantitative expression of the radon exhalation rate,the thickness of the covering material,the porosity and the diffusion coefficient of the topmost covering material;(3)The transfering and changing regularity of radon in uranium tailings piles under non-coupling and coupling effects was analyzed.The comparative analysis result showed that the influence of effective seepage caused by temperature difference between the inside and outside of tailings piles on radon exhalation had nothing to do with the height of tailings piles,and the external load,temperature difference and seepage had significant impact on radon migration.Therefore,the multi-field coupling effect can not be neglected in the actual management projects;(4)According to the constructed multi-field coupling model,the visual simulation of spatial and temporal distribution of radon concentration in uranium tailings piles' coverage materials was carried out.In the coverage management of uranium tailings piles,the orthogonal experimental design method was used to analyze and study the best combinations,the primary and secondary orders and significance of porosity,diffusion coefficient,density,permeability,adsorption coefficient and material types;the intuitive analysis was used to analyze the best combinations,the primary and secondary orders of the factors affecting radon migration and management cost;the variance analysis was used to analyze the significance of affecting factors.And taking one uranium tailing pile management project as an example,the order of advantages and disadvantages of alternative coverage materials was obtained based on orthogonal experiment analysis;(5)According to the mathematical equation of radon migration in coverage materials,the multi-layer coverage model was established under the constraints of material cost,cover thickness and construction period.Taking the three-layer covering system of uranium tailing piles management project as an example,the immune genetic algorithm was adopted to optimize the thickness and diffusion coefficient of the covering material in the covering system,to study the weight of influencing factors of radon exhalation rate,and to make comparative analysis of the orthogonal experimental results.