Empirical Principles of Long-Term Prediction of Radioactive Contamination of Water Bodies

The mechanisms of formation of long-term radioactive contamination of rivers after the Chernobyl accident are discussed. By estimation, the largest contribution to the contamination of surface waters is made by the wash-off 66%, about 33% is due to the desorption from bottom sediments and 11% is accounted for by the atmospheric depositions. Based on the data of radiation monitoring in the Tula and Kaluga regions, it has been shown that the reduction in 137Cs concentration in water obeys the exponential law with the half-reduction period of about 1.3 years. Arguments are presented to suggest that the exponential law of the decrease of concentration in river water is due to removal of radionuclides from the upper exchangeable layer of the soil. The thickness of this layer is estimated at 1 cm. The results of the analysis can serve as a basis for creating models for long-term prediction of contamination of water bodies as a result of radioactive fallout on the catchment area.