ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-4245-2012 Global risk of radioactive fallout after major nuclear reactor accidents Lelieveld J. 1 2 Kunkel D. 1 Lawrence M. G. 1 3 Max Planck Institute for Chemistry, P.O. Box 3060, 55020 Mainz, Germany The Cyprus Institute, Nicosia, Cyprus now at: The Institute for Advanced Sustainability Studies, Potsdam, Germany 12 05 2012 12 9 4245 4258 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/4245/2012/acp-12-4245-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/4245/2012/acp-12-4245-2012.pdf

Major reactor accidents of nuclear power plants are rare, yet the consequences are catastrophic. But what is meant by "rare"? And what can be learned from the Chernobyl and Fukushima incidents? Here we assess the cumulative, global risk of exposure to radioactivity due to atmospheric dispersion of gases and particles following severe nuclear accidents (the most severe ones on the International Nuclear Event Scale, INES 7), using particulate <sup>137</sup>Cs and gaseous <sup>131</sup>I as proxies for the fallout. Our results indicate that previously the occurrence of INES 7 major accidents and the risks of radioactive contamination have been underestimated. Using a global model of the atmosphere we compute that on average, in the event of a major reactor accident of any nuclear power plant worldwide, more than 90% of emitted <sup>137</sup>Cs would be transported beyond 50 km and about 50% beyond 1000 km distance before being deposited. This corroborates that such accidents have large-scale and trans-boundary impacts. Although the emission strengths and atmospheric removal processes of <sup>137</sup>Cs and <sup>131</sup>I are quite different, the radioactive contamination patterns over land and the human exposure due to deposition are computed to be similar. High human exposure risks occur around reactors in densely populated regions, notably in West Europe and South Asia, where a major reactor accident can subject around 30 million people to radioactive contamination. The recent decision by Germany to phase out its nuclear reactors will reduce the national risk, though a large risk will still remain from the reactors in neighbouring countries.

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