TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 52, 2018

Analysis of two forms of radioactive particles emitted during the early stages of the Fukushima Dai-ichi Nuclear Power Station accident

Yukihiko Satou1*, Keisuke Sueki1, Kimikazu Sasa1, Hideki Yoshikawa2, Shigeo Nakama2, Haruka Minowa3, Yoshinari Abe4, Izumi Nakai4, Takahiro Ono4, Kouji Adachi5 and Yasuhito Igarashi5

1Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8577 Japan
2Fukushima Environmental Safety Center, Japan Atomic Energy Agency, 10-2 Fukasaku, Miharu, Tamura-gun, Fukushima, 963-7700 Japan
3Radioisotope Research Facility, Jikei University School of Medicine, 3-25-8, Nishi-shimbashi, Minato, Tokyo, 105-8461 Japan
4Department of Applied Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601 Japan
5Atmospheric Environment and Applied Meteorology Research Department, Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki 305-0052 Japan

(Received August 1, 2017; Accepted December 11, 2017)

Abstract: Two types of radioactive particles were isolated from environmental samples collected at various distances from the Fukushima Dai-ichi Nuclear Power Station. "Type A" particles are 2–10 μm in diameter and display characteristic Cs X-ray emissions when analyzed using energy-dispersive X-ray spectrometry (EDS). "Type B" particles are considerably larger, up to 400 μm in diameter, with Cs concentrations too low to be detectable with EDS. These larger particles were isolated from the region north of the nuclear reactor site, which was contaminated on March 12, 2011. The specific activity of Type B particles is much lower than Type A, and the mean 134Cs/137Cs ratios are ∼0.93 and 1.04, respectively. The Type B ratio indicates that power station Unit 1 is the source, implying that these larger radioactive particles were discharged on March 12. This study found that different type of radioactive particles were released not only on March 15 but also on March 12.
Key words: Fukushima Dai-ichi Nuclear Power Station accident, Radioactive Particles, Caesium isotopic ratio, Hydrogen explosion, Specific radioactivity

*Corresponding author E-mail: satou.yukihiko@jaea.go.jp

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