Estimating parameters of hydrodispersion and its impact on convective-diffusive transfer of radioactive contamination in natural dispersive media

This article presents explicit analytical dependencies of the hydrodispersion coefficient of radionuclides on the moisture flow rate and the characteristics of their sorption during convective-diffusive transport in natural dispersed media. These dependencies are obtained based on the analysis of the asymptotic solution of the convective-diffusive transport equation for radionuclides, taking into account their non-equilibrium sorption and the presence of molecular diffusion. It has been shown that the coefficient of hydrodispersion of radionuclides has a quadratic dependence on the moisture flow rate and an inverse dependence on the mass transfer coefficient between radionuclides in the pore solution and those sorbed by the solid component of the dispersed medium. In the active layer of the territory, where there are periodic changes in the magnitude and direction of the convective moisture flow rate, it is recommended that the calculation of the convective-diffusive transfer of radionuclides be carried out with due consideration of the non-equilibrium nature of their sorption by the solid component. It has been established that in the active layer, the main contribution to the transport of radionuclides is made by hydrodispersion, which is determined by the average integral value of the square of the convective moisture flow velocity, and effective molecular diffusion. This results in a relatively low rate of transport of radionuclides in the active layer in the direction of aquifers, in the absence of closed catchment areas of slope runoff.

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