Radioactive source terms for the Fukushima nuclear accident

A large amount of radioactivity was released into the environment after the Fukushima nuclear accident (FNA) in Japan in 2011. This radioactivity had a significant impact on the global environment, and there was much public concern about its effects. The subsequent assessment of the FNA and the environmental remediation required are proving to be long and complicated tasks. The assessments are based on the radioactive source terms for the FNA, which determine the level of damage caused by the nuclear accident. We investigated the radioactive source terms from three aspects: the amount and composition of the radionuclides; the activity and atomic ratio of the radionuclides; and comparison with other historical events. The total amount of radioactivity, excluding the radioactive noble gases (85Kr and 133Xe), released by the FNA was about 10% of that released by the Chernobyl nuclear accident in 1986 and <1‰ of the global fallout from the atmosphere nuclear explosion. However, the FNA was the most serious nuclear accident in terms of radioactive pollution of the marine environment. The recovery actions carried out after the FNA have been evaluated and the environmental impacts of the FNA are discussed.