Abstract: A uranium tailings dam in northern China was selected as the research object to collect uranium tailings samples in tailings dams,aquifer sand samples and water barrier clay samples.The isotherm adsorption law of U on soil samples and the leaching process of U under rainfall conditions were studied to obtain U adsorption and migration parameters in key strata and the release rule of source terms.Using FEFLOW6.2 software to establish a three-dimensional model of groundwater in the uranium tailings evaluation area,simulating U migration behavior and concentration distribution.The results show that the adsorption of U on sand and clay conforms to the linear isothermal adsorption model,the distribution coefficients k_d are 20.41 L/kg and 45.92 L/kg respectively.The equilibrium concentrations of U under acid rain leaching and deionized water leaching conditions during the experiment period were 0.83 mg/L and 0.79 mg/L,respectively.And the leaching rates were 46.07% and 20.92%,respectively.The simulation results show that after 30 years of migration,the maximum concentration of U in groundwater will reach 0.595 mg/L and the peak concentration migration distance is 36.44 m.After 50 years of migration,the maximum concentration of U in groundwater will reach 0.440 mg/L and the peak concentration migration distance is 42.93 m.

Key words: uranium tailings, distribution coefficient, leaching experiment, groundwater mathematical simulation, nuclide migration