Consequences for Norway from a hypothetical accident at the Sellafield reprocessing plant: Atmospheric transport of radionuclides

The potential consequences for Norway should a nuclear accident at the Sellafield nuclear site occur, have been of concern for Norwegian authorities for several decades. Meteorological data from a 33-year period and the dispersion model ‘SNAP’ were used to evaluate meteorological conditions for which atmospheric transport of radionuclides from Sellafield to Norway would lead to the most severe impacts. The worst-case meteorological scenario for Norway, was found on 25th June 1989 for a low elevation (0–800 m) release and on 29th June 2001 for a higher elevation (800–1600 m) release. In both cases the western part of Norway was most affected. In general, the probability for depositions (>10 Bq/m2 of 137Cs) increased about 40% during the autumn and winter compared to the spring and summer months. An influence of climate change on the depositions was analysed, but not verified. Results from a number of simulations were also compared to identify how factors such as radioactive particle characteristics and initial release conditions could affect the predicted radionuclide deposition. The impact on predicted total depositions as well as hot-spot depositions by varying particle density and size as well as release elevation in worst-case scenario simulations amounted to about 40%–50%.