Simulating transport of uranium series radionuclides in fractured rock of Beishan area: The use of multi-channel model and the influence of parameters

In this work, the multi-channel model is applied to simulate transport of radionuclides for uranium series in Beishan area of China. In the model, the mechanisms of advection, velocity dispersion, surface retardation, matrix diffusion and sorption, and radioactive decay are considered. The simulation results show that the normalized concentration of U-238 has the largest value of at about yr, while the highest concentration of all daughter nuclides is in the range of . Moreover, it is found that a decrease in mean aperture of the ensemble of channels causes an earlier arrival of U-238, because of the increase of the fluid velocity of each channel. Similarly, a higher mean flowrate or a smaller average width also leads to an earlier arrival. In addition, it is also observed that early-time behaviors are significantly different, provided that the amount of flow-paths is limited. An increased amount will reduce the difference, since the realization mean flowrate is closer to the statistical mean value of the infinite amount case. Likewise, the effect of heterogeneity of rock matrix on radionuclide transport is also dependent on the number of flow-paths.