Testing Study On Na、Cu、U Transport In Granite Rock

In recent years, some problems such as the groundwater pollution, site selection of high-level radioactive waste disposal repository make the study of solute in porous media migration became the research hotspot. Compared with the solute transport in porous media, the study of solute transport in fracture is still in the initial stage. The experimental simulation about the migration of Na, Cu and U is completed by self-made granite solute transfer equipment. Simulation includes: 1) Na, Cu and U in granite diffusion experiment; 2) Na, Cu and U in granite dispersion experiment; 3) Na, Cu and U in single fractured granite convection-dispersion experiment; 4) Na in granite in single fractured diffusion coefficient of scale effect experiment. On the basis of the experimental data, we use the wiring method to calculate the diffusion coefficient, dispersion coefficient, retardation coefficient, longitudinal disperse coefficient and transverse dispersion coefficient of Na, Cu and U. These parameters can provide the basis for mathematical simulation.The conclusion can be found as follows:(1) It can be found from the diffusion and dispersion experiment that concentration difference and block of granite are due to the larger difference of concentration change rate in the original and the liquid taking tank. And the concentration of the elements in the dispersion experiment equipment is higher than that the element concentration in the diffusion experiment. Besides we conclude that of the concentration change rate each element in granite is U>Na>Cu from contrast Na, Cu, U diffusion and dispersion curve, because the block degree each element in granite is Cu>Na>U. The diffusion coefficients of Na, Cu and U are respectively is 8.57×10-13 m2/s、6.45×10-13 m2/s、1.03×10-12 m2/s,retardation coefficient are respectively is 6214、12047、2031; The dispersion Na, Cu and U are respectively is 4.83×10-12 m2/s、5.35×10-12 m2/s、3.08×10-13 m2/s,and retardation coefficient are respectively is 6079、12005、1705. Finally during the experiment, in the rigorous calculation of the volume of sampling conditions, the liquid surface of high concentration box will be increased, presumably because granite slab become semipermeable membrane.(2) Granite fracture migration curves of experiment of Na, Cu and U as a whole is an inverted "V" shape by including molecular diffusion and mechanical dispersion. With the increase of migration time and distance, peak concentration decreases gradually, peak area increases gradually, migration curve "shrink" weakened and the "tail" phenomenon is obvious. Contrast of Na, Cu and U migration curves: curve "shrink" phenomenon: U > Na > Cu, curve "tail" phenomenon of Cu > Na > U, presumably in granite of the three elements the inhibition of Cu > Na > U; In addition longitudinal disperse coefficient of Na, Cu, and U respectively is 0.0858~0.1077 m, 0.0921~0.1162 m, 0.0958~0.1337 m; The transverse dispersion Coefficient respectively is 0.00077 m, 0.00066 m, 0.00030 m(3) It is shown that small scale experiment can also produce the "scale effect" from the "scale effect" experimentNumerical simulation study mainly includes two aspects:1) Based on the convection-diffusion experiment, choosing dual continuous media model build mathematical model of instantaneous injection to verify related parameters.2) With field practical situation, choosing dual continuous media model build mathematical model of constant injection mathematical to predict grey granite as the occurrence of contaminated material, Na, Cu and U in the cracks of migration.The conclusion can be found as follows:(1) Comparing with the experimental transport data and simulate the migration curves, we found that the experimental data is accuracy. Under the condition of more unknown parameter, it is feasible that using equivalent continuum theory could get pertinent parameters.(2) Under the condition of simulation of Na, Cu, U migration in the grey granite fissure, it is found that the concentration of each element is also increased with the migration time increasing and the solute migration in the same location. The block coefficient of Na, Cu, U in the granite synchronised instant is difference due to the difference of solute migration distance which is U>Na>Cu. But with the increase of Na, Cu and U migration distance in the fracture, the relative concentration of the matrix decreased. The diffusion depth of Na、Cu、U in the substrate is U>Na>Cu at the same location. And the concentration is still maintain U>Na>Cu in the same the diffusion substrate depth, which is caused by that the block coefficient of each element is different in the granite.