Applicability of the convection-diffusion mechanism for modeling migration of 137Cs and 90Sr in the soil

The convection-diffusion equation is analyzed as a basis for modeling the migration of radionuclides. To describe the experimental data adequately within the framework of the diffusion-convection equation, it is necessary to introduce migration parameters which increase as the radionuclides penetrate further down through the soil layer and decrease as the observation time lengthens. The assumption that sorption processes in the migration of 137Cs and 90Sr are linear seems to be unjustified. The stochastic model helps us to overcome the main problems of the diffusion-convection approach, but it needs to be tested on a wider range of experimental material.