The Dynamic of the Model Parameters Of

Knowledge of the distribution in soil of radionuclides deposited following the release their to the environment is important for a reliable assessment of external dose and root uptake by plants. In order to predict the downward migration of radionuclide we should know the evolution in time the parameters of the model describing distribution of the radionuclide in soil layer. In this paper diffusion model was applied to describe distribution of Cs-activity concentration in soil profile of 3 sites located on soddy-podzolic and soddy soils. And the convection-diffusion equation was applied to 3 sites situated on peaty-gley ang peaty-boggy soils. Soil samples have been collected during 19892001 years at the southern of Belarus. Earlier, some authors studied the dynamic of the parameters of convection-diffusion model and pointed out a decrease with time these parameters in several soils. However, the period of investigation was short and they didn't give an exact relationship between parameters and time. Our analyses of the dynamic of diffusion (D) and convection (V) coefficients showed that D didn't change for sites with soddy soils during the period of investigation. The prognostic calculations of Cs-activity concentration in soil layer with constant value D were carrying out for these sites. At the same time D and V for sites with peaty soil decreased with time. This decrease was well described by power function (f=at). Obtained dependencies D(t),V(t) were used for prediction of Cs activity concentration in soil layer of sites with peaty soil.