Numerical Simulation Of Radionuclide Migration In Granite Fractured Media

It’s generally considered that the granite rock mass is one of the most suitable media fordeep geological disposal of radioactive waste. When the repository’s engineering barrier isfailed, the fissures in granite rocks can provide channels for groundwater storage andradionuclide migration, and the radionuclides may migrate and diffuse with the groundwaterflow and therefore influence the ecological environment. Studying the radionuclide migrationin fractured granite media is of great significance for evaluating the disposal of radioactivewaste.According to the nuclide migration law in a single fractured rock, based on thedual-continuum model, this paper derives and summarize the nuclide transport equations infracture of parallel plate single fractured media and matrix. The exponential attenuation at theentrance of the fissures is considered, combined with the coupled adsorption of nuclides at theinterface of fracture and matrix, the analytical solution of nuclide’s relative concentrations inmatrix and fissure is got with Laplace transform and the computer program has also beencompiled. The239Pu is selected in the simulation process. Combined with the permeabilitycoefficient, the partition coefficient and other parameters of the study area, the relativeconcentration distributions in fracture and matrix in granite rock mass of the study area areanalyzed, and the migration and trends of239Pu in fracture and matrix are predicted.Simulations show that239Pu diffuses very slow in matrix--it diffuses only a few millimeterswhile about migrates3meters in fracture within0.5×105years. Simulation results also showthat the granite rock area can be used to dispose radioactive waste containing239Pu. Theaffection of parametric variations to the nuclides migration in fracture is also studied, such asthe time, the average water speed in fracture, gap width, permeability coefficient, rockporosity, radionuclide half-life, block coefficients in matrix and fissure. The results show thatthe nuclide migration range will increase when the time, the average water speed in fissure,gap width, permeability coefficient or the radionuclide half-life increase, while it willdecrease when the rock porosity, retardation coefficient in matrix and fissure increases.