18 Janvier 2016
Georg Steinhauser†⊥¶, Tamon Niisoe‡, Kouji H. Harada§, Katsumi Shozugawa∥, Stephanie Schneider⊥, Hans-Arno Synal#, Clemens Walther⊥, Marcus Christl#, Kenji Nanba¶, Hirohiko Ishikawa‡, and Akio Koizumi*§
† Colorado State University, Environmental and Radiological Health Sciences, Fort Collins, Colorado 80523, United States
‡ Research Division of Atmospheric and Hydrospheric Disasters, Disaster Prevention Research Institute, Kyoto University, Uji 6110011, Japan
§ Department of Health and Environmental Sciences, Kyoto University Graduate School of Medicine, Kyoto 6068501, Japan
∥ Graduate School of Arts and Sciences, The University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan
⊥ Leibniz Universität Hannover, Institute of Radioecology and Radiation Protection, D-30419 Hannover, Germany
# Laboratory of Ion Beam Physics, ETH Zürich, CH-8093 Zürich, Switzerland
¶ Institute of Environmental Radioactivity, Fukushima University, Fukushima 960-1296, Japan
Environ. Sci. Technol., 2015, 49 (24), pp 14028–14035
Publication Date (Web): October 8, 2015
Copyright © 2015 American Chemical Society
*E-mail: firstname.lastname@example.org. Phone: 81-75-753-4456. Fax: 81-75-753-4458.
ACS AuthorChoice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.
The Fukushima nuclear accident (March 11, 2011) caused the widespread contamination of Japan by direct deposition of airborne radionuclides. Analysis of weekly air filters has revealed sporadic releases of radionuclides long after the Fukushima Daiichi reactors were stabilized. One major discharge was observed in August 2013 in monitoring stations north of the Fukushima Daiichi nuclear power plant (FDNPP). During this event, an air monitoring station in this previously scarcely contaminated area suddenly reported 137Cs activity levels that were 30-fold above the background. Together with atmospheric dispersion and deposition simulation, radionuclide analysis in soil indicated that debris removal operations conducted on the FDNPP site on August 19, 2013 are likely to be responsible for this late release of radionuclides. One soil sample in the center of the simulated plume exhibited a high 90Sr contamination (78 ± 8 Bq kg–1) as well as a high 90Sr/137Cs ratio (0.04); both phenomena have usually been observed only in very close vicinity around the FDNPP. We estimate that through the resuspension of highly contaminated particles in the course of these earthmoving operations, gross 137Cs activity of ca. 2.8 × 1011 Bq has been released.
[ …] In summary, this study reveals significant intermittent releases of airborne radionuclides in August 2013, long after the initial releases caused by the Fukushima nuclear accident in spring 2011. Increased activities were observed at the air filter station in Haramachi/Minamisoma in the week of August 15 to 22, 2013. Although the resuspension of deposited radionuclides has been identified as a potent source for transport of radioactive contaminants,(24, 25) we could show herein that in fact the site of FDNPP is likely to be the source of one of the most pronounced sporadic releases since the accident. Modeling confirms that debris removal actions taking place in this week are likely to have contaminated the area of Minamisoma that has had very low contamination levels previously. Total 137Cs and plutonium deposition as well as 134Cs/137Cs activity ratios and 240Pu/239Pu isotopic ratios observed in soil remain inconclusive to support the hypothesis. However, one extraordinary high contamination of soil with 90Sr in the center of the simulated plume indicates the contamination of the location with dust particle stemming from the FDNPP site. The high non-uniformity of the contamination levels and 134Cs/137Cs signatures is most probably due to non-uniform deposition of radioactive particulate matter, causing high local fluctuations in the soil samples taken in the course of this study. Our results indicate that a total of 2.8 × 1011 Bq 137Cs has been released from the FDNPP site by resuspension in the course of the debris removal operations on August 19, 2013. This release corresponds to approximately 1/50 000 of Fukushima’s total atmospheric releases of 137Cs (14.5 PBq).(33) Finally, this study evidences that significant secondary releases of radionuclides by resuspension processes and eolian transport of contaminated particles are conceivable scenarios in the future. Most importantly, the ongoing decommissioning and dismantling activities of the crippled Fukushima reactors, thereby, pose an imminent health threat for future decades. A resuspension of highly contaminated particles from the FDNPP site not only involves the risk of a massive radiocesium dispersion; these particles are likely to carry an even more hazardous load such as less volatile, bone-seeking 90Sr or actinides (including plutonium).