Reconstruction of the long-term dynamics of radioactive cesium in water bodies contaminated as a result of nuclear accidents (case studies of Chernobyl and Fukushima)

The study is focused on the reconstruction of long-term dynamics of ¹³⁷Cs concentration in water bodies contaminated as a result of Chernobyl and “Fukushima-1” NPP accidents. It was found that the vertical distribution of ¹³⁷Cs in bottom sediments of deep-water sites could be a basis for reconstruction of the dynamics of radionuclide concentration in suspension and in solution. Columns of bottom sediments of reservoirs and experimental values of distribution coefficient Kd are used for reconstruction. The method is applicable in the absence of mixing of the deposited suspension with the underlying layers and at Kd values significantly higher than 104 l/kg. Studies in the Chernobyl and “Fukushima-1” NPP contamination zones have shown that it is possible to reconstruct the long-term changes of ¹³⁷Cs concentration for rivers, lakes and ponds. The obtained data are the first assessment of the time course of ¹³⁷Cs specific activity on suspended sediment in water bodies of the Chernobyl NPP zone, which is important for understanding its behavior in the soil-water system and its migration through food chains. The time dependences of ¹³⁷Cs concentrations are described by the empirical two-exponential and/or semi-empirical diffusion model, applicable for predictive assessments of the long-term dynamics of radioactive contamination in water bodies after nuclear accidents. The results of the study are confirmed by monitoring data for the test water bodies, showing satisfactory agreement with the reconstructed values of ¹³⁷Cs concentrations. The information obtained is important for assessing the environmental consequences of nuclear accidents and developing strategies for the management of contaminated areas. The methodology presented in the study could be adapted to study the behavior of other radionuclides in aquatic ecosystems, contributing to better prediction and management of radioecological risks over a long term horizon.

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