Study On Fractal Dynamics Of Radioactive Pollutants In Uranium Tailings

With the development of nuclear power industry in China,a large amount of uranium tailings have been produced during the mining and processing of uranium mines.Radionuclides contained in the uranium tailings,including radon and radon daughters,uranium,radium,etc.,can continuously migrate to surrounding rock,soil,air,groundwater and other places through diffusion-seepage,thus lead the problem of radioactive safety to the surrounding environment.What's worse,with the accumulation over time,if not effectively prevented and controlled in time,radionuclides will have adverse effects on people's production,life and even health,and may eventually threaten the order and safety of economic society.The study on the geometrical structure of uranium tailings plays an important role in the prevention and control of radioactive pollutants.Based on the fractal theory and the self-similar structure characteristics of uranium tailings,this paper analyzes the fractal structure characteristics of uranium tailings,such as the particle size,surface morphology,maximum pore size distribution,and studies the fractal dynamics mechanism of gas diffusion.In addition,the fractal geometry model of uranium tailings is constructed,and then the micro-structure of uranium tailings,such as a pore,is quantitatively described and reconstructed,The theoretical models of fluid percolation and gas diffusion are established and numerical simulation is carried out to analyze and discuss the influencing mechanism of various factors on fractal characteristics.The main research results are as follows:(1)A fractal structure model of uranium tailings was constructed.Based on the fractal geometry theory and main physical parameters of uranium tailings,the fractal model of particle size distribution,the fractal model of surface morphology and the fractal model of maximum pore size were constructed.The results show that different uranium tailings sand particle size composition can change the fractal dimension,In addition,the particle size,surface roughness and pore structure of uranium tailings have fractal geometry distribution characteristics,and the influence of the main micro parameters on the fractal structure is discussed through model prediction.(2)The influence of permeability and imbibition of uranium tailings on the distribution of maximum pore size was studied,and the influence of physical parameters such as particle size,porosity and permeability on the structural mechanism of uranium tailings was revealed.It is found that there is a close relationship between the parameters.Comparing the predicted value of the maximum aperture fractal model with the experimental value,the practicability of the model has been verified.(3)The fractal model of gas diffusion coefficient was constructed,and the predicted value of the fractal model of effective gas diffusion coefficient was fitted with the experimental value.It is found that the model highly consistent with the experimental value.Then,the fractal dynamics mechanism of radon emission was studied,and the movement process of radon atom was discussed.Combined with the pure diffusion model of radon in uranium tailings,the timevarying migration process of radon concentration in uranium tailings was simulated.It is found that the time-varying diffusion of radon in uranium tailings is a relatively complex and irregular movement process with certain fractal characteristics.