Abstract
The Great East Japan Earthquake that occurred on 11 March 2011 generated a series of massive tsunami waves that caused severe damage to the Fukushima Daiichi Nuclear Power Plant, following which large amounts of radioactive materials were discharged from the power plant into the environment. Given the recently developed technologies for unmanned helicopters and their potential application in airborne radiation monitoring, we developed a radiation monitoring system for aerial use. We then used unmanned helicopters to measure the radiation level in areas with soil contaminated by radiocesium emitted from the nuclear power plant to evaluate the ambient dose rate distribution around the site. We found that in dry riverbeds downstream of the highly contaminated watershed, especially in the upstream parts, that the ambient dose rate was higher than that in protected inland areas. In addition, we carried out soil sampling in dry riverbeds. The soil sample data agreed with the results obtained from the unmanned helicopter. A possible scenario is that river sediment and adjacent soil containing radioactive materials were carried downstream due to an event such as a rise in water level caused by, e.g., a typhoon, and that these remained in the riverbed after the water drained away. The vertical profile of radiocesium in the soil and the measurements of river sediment at river mouth areas corroborated this scenario.
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Acknowledgements
This survey used some of the results of a project commissioned by the Cabinet Office (Decontamination Pilot Projects for the Environmental Remediation of Evacuation Areas Contaminated with Radioactive Materials Discharged from the Fukushima Daiichi Nuclear Power Plant Accident). We thank General Manager Tetsuo Matsumoto, Specially Appointed Professor Ishi Mihashi, and Assistant Professor Yukiko Okada, of the Atomic Energy Research Laboratory, Tokyo City University, for analyzing samples using germanium semiconductor devices. We also thank Dr. Tatsuo Torii of JAEA for supervising all the research and surveys, as well as Mr. Kiyofumi Tsuchida of JAEA for guiding the surveys at the sites while also considering safety. We also thank Fukushima Prefecture for providing water level data. This study follows all the applicable current laws of Japan.
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Azami, K., Ootagaki, T., Ishida, M. et al. Characteristics of radiocesium contamination of dry riverbeds due to the Fukushima Daiichi Nuclear Power Plant accident assessed by airborne radiation monitoring. Landscape Ecol Eng 14, 3–15 (2018). https://doi.org/10.1007/s11355-017-0332-z
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DOI: https://doi.org/10.1007/s11355-017-0332-z