Observations of Atmospheric Radionuclides from the Fukushima Nuclear Accident in Tsukuba, Japan

Our observational research activity at the Meteorological Research Institute, Japan (MRI) on the atmospheric radioactivity is introduced in this presentation. Triggered by the Bikini incident in 1954, MRI has carried out observations of the atmospheric radionuclides, which are long-lived with potentials of environmental and health impacts. In order to clarify temporal change in concentration of anthropogenic radionuclides in the atmosphere and its control factors, the observations have continued over the long period. Especially, long-term observation record of monthly depositions of anthropogenic radionuclides, Sr-90 and Cs-137, becomes the world-longest; it covered full 55 years in March, 2012 since April, 1957. The accident of Fukushima Dai-Ichi Nuclear Power Plant of the Tokyo Electric Power Corporation, which occurred by the hit of great earthquake in March 11, 2011, emitted new radioactive material, which is at least a few tenth of those from the Chernobyl accident, to the atmospheric environment. By this large-scale contamination, atmospheric environments over Japan, especially the eastern part, were substantially impacted with a massive amount of the anthropogenic radionuclides. At the MRI, atmospheric monitoring and analysis of the radioactivity in the samples were continued before and after the accident. The impacts of the Fukushima accident are addressed and documented in our long-term time series of the atmospheric radioactivity.