239+240Pu in the Barents Sea Regions. Sources and radioecological assessment

The radioecological assessment for 239+240Pu in the Barents sea regions was made using the compartment modelling approach. The following sources of radioactive contamination were under consideration: global fallout from atmospheric testing of nuclear weapons, transport of 239+240Pu from the Sellafield and La Hauge nuclear plants and underwater testing of nuclear weapons in Chernaya Bay, Novaya Zemlya. The box model developed at NRPA uses a modified approach for compartmental modeling, which takes into account the dispersion of radionuclides over time. The box structures for surface, mid-depth and deep water layers have been developed based on the description of polar, Atlantic and deep waters in the Arctic Ocean and the Northern Seas, as well as site-specific information for the boxes. The volume of the three water layers in each box has been calculated using detailed bathymetry together with Geographical Information Systems. The box model includes the processes of advection of radioactivity between compartments, sedimentation, diffusion of radioactivity through pore water in sediments, resuspension, mixing due to bioturbation, particle mixing and a burial process for radionuclides in deep sediment layers. Radioactive decay is calculated for all compartments. The contamination of biota is further calculated from the known radionuclide concentrations in filtered seawater in the different water regions. Doses to man are calculated on the basis of seafood consumptions, in accordance with available data for seafood catches and assumptions about human diet in the respective areas. Dose to biota are determined on the basis of calculated radionuclide concentrations in marine organisms, water and sediment, using dose conversion factors. Results of the calculations show that atmospheric deposition is the dominant source for the Barents Sea, except for the Chernaya Bay region. It is also demonstrated that the impact of the Sellafield nuclear facilities has slightly grown in recent years, possibly because of remobilization from the sediment in the Irish Sea. From the calculations of 239+240Pu concentrations, we can see that there is a relatively good correspondence between the results of the model and the available experimental data for the water and sediment compartments. The calculations show that the estimated doses from 239+240Pu to a hypothetical group with a high consumption of seafood (a critical group) are significantly lower than doses from natural sources. Dose comparison indicates that benthic marine organisms are the most sensitive group of biota for the present investigation. (authors)