Modelling of radionuclide transfer in rivers and reservoirs. Validation study performed within the IAEA/CEC VAMP programme

The comprehensive data obtained for different rivers after the Chernobyl accident, primarily the data from the heavily contaminated Pripyat river-Dnieper river-reservoir system, provide a unique basis for validations and improvements of transport models for aquatic radionuclides. These data were used in two scenarios by the River Sub-Group of the Aquatic Working Group of the IAEA/CEC co-ordinated research programme Validation of Environmental Model Predictions (VAMP). For one model validation scenario, the Clinch River-Tennessee River system, contaminated by releases from the Oak Ridge National Laboratory, was chosen. The data collected during the post-Chernobyl period, related to the Pripyat river and to the Dnieper river and reservoirs, were used in the other scenario. Different kinds of models were applied, and the data from the two scenarios were used to simulated the dynamics of radionuclides in water, suspended sediments and bottom sediments. Analytical models, two kinds of box models and two kinds of one-dimensional (cross-sectionally averaged) models were used for the simulation of radionuclide concentrations in water and sediments. These models represented different levels of model complexity for the description of interactions between radionuclides, suspended sediments and sediments deposited on the bottom layer. The vertical profiles of radionuclides in bottom sediments were simulated for the Tennessee River scenario by the multilayers bottom model and by two kinds of vertical diffusion models. For this scenario, the modelling of radionuclide distribution in the aquatic food-chain, mainly in fish, was based on static approaches. For the other scenario, the temporal changes in 137Cs concentrations in bream, trench and Carpio carpius in the Kiev reservoir (Dneiper river) were simulated by the dynamic model. The doses to the population via aquatic pathway were calculated on the basis of simulated concentrations in an environmental compartment and were used in analyses of the role of aquatic pathways in the formation of the total radiation dose after large releases. (author). 12 refs, 4 figs