Atmospheric transport of radionuclides following hypothetical reactor accidents

In this work two reactor accident scenarios were studied using the SILAM dispersion model developed in the Finnish Meteorological Institute. The accident scenarios were the planned nuclear power plant at Pyhajoki, Finland and the planned floating nuclear reactor at the Shtokmann gas field in the Barents Sea. The calculated atmospheric concentration and deposition values were compared to those measured after the atmospheric nuclear tests of the 1950s and the 1960s and the 1986 Chernobyl accident. To obtain data on the atmospheric concentration of radionuclides in the air since the 1960s a set of archived aerosol samples was analysed for radioactivity. In the case of a hypothetical reactor accident at Pyhajoki the average cesium-137 deposition would be about the same as the maximum values observed in Finland after the 1986 Chernobyl accident. In Finnish Lapland north of Rovaniemi the exposure would be at its maximum 170 times higher than the exposure in 1986. The floating reactors planned to the Barents Sea contain relatively low amounts of radioactivity and thus the consequences of a hypothetical reactor accident would remain quite local. For example the deposition of plutonium-241 would be less than 10 Bq/m which is one per cent of the deposition after the atmospheric nuclear tests. The SILAM results were also compared with the results obtained with the SNAP model operated by the Norwegian Meteorological Institute. In most cases the models gave quite comparable results. The biggest differences are related to the occurrence of precipitation and its effect on the wet deposition. Publishing unit Arctic Research Classification (UDK)