Emission of spherical cesium-bearing particles from an early stage of the Fukushima nuclear accident / 福島原子力発電所事故の初期段階に放出されたセシウムを含む球状粒子

Kouji AdachiMizuo KajinoYuji Zaizen Yasuhito Igarashi
Received 12 June 2013 | Accepted 15 August 2013  | Published 30 August 2013

The Fukushima nuclear accident released radioactive materials into the environment over the entire Northern Hemisphere in March 2011, and the Japanese government is spending large amounts of money to clean up the contaminated residential areas and agricultural fields. However, we still do not know the exact physical and chemical properties of the radioactive materials. This study directly observed spherical Cs-bearing particles emitted during a relatively early stage (March 14–15) of the accident. In contrast to the Cs-bearing radioactive materials that are currently assumed, these particles are larger, contain Fe, Zn, and Cs, and are water insoluble. Our simulation indicates that the spherical Cs-bearing particles mainly fell onto the ground by dry deposition. The finding of the spherical Cs particles will be a key to understand the processes of the accident and to accurately evaluate the health impacts and the residence time in the environment.


An earthquake with a magnitude of 9.0 occurred in Japan on March 11, 2011. In addition to the earthquake itself, a tsunami struck along the east coast of Honshu and damaged the Fukushima Daiichi nuclear power plant (FNPP). The FNPP eventually lost its ability to cool the nuclear fuel, which caused hydrogen explosions and released radioactive materials into the environment. Because of the local contamination, many people still cannot return home. Currently, the Japanese government is spending considerable amounts of money to clean up the contaminated residential environment and agricultural fields. The radioactive materials released to the atmosphere traveled over the entire Northern Hemisphere. In Europe, for example, Masson et al. measured increases in radioactive cesium and iodine in the air from March 19, 2011 and showed that the maximum levels occurred between March 28 and 30. Although the accident has global impacts, we still do not know exactly what happened in the reactors during the accident, and the estimates of the radioactive Cs releases vary largely from 9 to 36 PBq. The chemical and physical properties (i.e., chemical forms, particle sizes, shape, phases (gas or aerosol), water solubility, and residence time) of the radioactive materials released into the environment are not well known. Such knowledge is necessary to improve the numerical models to estimate the geographical distributions and evaluate the human exposures during and after the accident. Because the mass of released radioactive material was small, i.e., the release of 137Cs from the accident was <20 kg, and the material spread globally, it is extremely difficult to chemically detect it other than by radioactivity detectors. In this study, we chemically detected Cs within single particles for the first time by using electron microscopy and report the shape, composition, water solubility, and sizes of the particles to evaluate the implications of their formation process, occurrences in the environment, and potential health effects. This knowledge is still important for preventing further accidents, finding effective ways to remove the radioactive materials from the environment, and preventing further resuspention of the materials.

足立 光司, 梶野 瑞王, 財前 祐二 & 五十嵐 康人
2013年8月30日 Scientific Reports 3 : 2554 doi: 10.1038/srep02554 (2013)


Kouji Adachi, Mizuo Kajino, Yuji Zaizen & Yasuhito Igarashi

Scientific Reports 3, Article number: 2554 | doi:10.1038/srep02554

受付日:2013年6月12日 承認日:2013年8月15日 公表日:2013年8月30日