Stochastic Simulation Research Of Uranium Migration In Shallow Groundwater At Uranium Mill-tailing Sites

All kinds of radioactive wastes generated in uranium exploitation and processing woulddo harm to environment safety. The purpose of this paper is to investigate transport principleof radiounclides in uranium mill-tailing sites employing fluid dynamics, complex science,stochastictheoryandcomputetechnology.Baseontheparticularconditionofcertainuraniummill-tailing site, the coupled model of radionuclide migration was set up to simulate themigrationofU(â…¥),byusingGMS,andthemodelparameterswereoptimized.The migration of uranium was simulated, inthegroundwater at the mill-tailing, byusingthe couple-model of the two-dimensional phreatic water and solute transport, on the basis ofgeneralized geohydrologic condition of the uranium mill-tailing. Comparing measured valuesto simulated ones of hydraulic head in observation well, model parameters were calibrated,and the reliability of the model was verified. The influence was discussed of dispersioncoefficient, retardation coefficient and time on the migration of U (â…¥). The results of thesimulation indicate that, the U(â…¥) concentration is decreasing with the enlargement ofdispersioncoefficientinthenearofthepollutionsources,justtheoppositeinthefar.Compareto the dispersion coefficient, in the same order of magnitude, retardation coefficient on theimpact of the U(â…¥) migration is far great than that of dispersion coefficient. When thesimulated time is 2000 year, the slope of concentration profile decrease; after 5000 year, thecurve slope is dropoff, which shows that the concentration of U(â…¥) in the soil trends tosaturation.The stochastic hydrogeology method is a new method for solving the flow and transportproblems in the heterogeneous aquifers. The Monte Carlo method, which bases on thestochastic theory, is applied, and on the assumption that the hydraulic conductivity fieldfollows a lognormal distribution, the mathematical model of parameter stochastic wasestablishedbyusingGMS.Theimpactsofthevariationofhydraulicconductivityonflowand the U(â…¥) migration were investigated in the groundwater at the mill-tailing site. The resultsshow that, both of the water head and the U(VI) migration of the groundwater at tailings damare greatly affected by the variability of hydraulic conductivity. Under the same conditions,the peak of the standard deviation contour of water head increases with the increase of thevariability of hydraulic conductivity, taking the form of decreasing trends from the tailingsdam to perimeter. And with the increase of the standard deviation of hydraulic conductivity,the range of U(VI) migration and the U(â…¥) concentration peak value increase, and thegradient of U(â…¥) concentration distribution decreases. In addition, the standard deviationdistribution of U(â…¥) concentration at the same nodes within the scope of U(â…¥) migrationincrease. The variety of the standard deviation of water head and U(â…¥) concentrationbasicallyreflectthatoftheheterogeneityofhydraulicconductivity.