New highly radioactive particles derived from Fukushima Daiichi Reactor Unit 1: Properties and environmental impacts

Kazuya Morooka; Eitaro Kurihara; Masato Takehara; Ryu Takami; Kazuki Fueda; Kenji Horie; Mami Takehara; Shinya Yamasaki; Toshihiko Ohnuki; Bernd Grambow; Gareth T W Law; Joyce W L Ang; William R Bower; Julia Parker; Rodney C Ewing; Satoshi Utsunomiya

doi:10.1016/j.scitotenv.2021.145639

New highly radioactive particles derived from Fukushima Daiichi Reactor Unit 1: Properties and environmental impacts

Sci Total Environ. 2021 Jun 15:773:145639. doi: 10.1016/j.scitotenv.2021.145639. Epub 2021 Feb 5.

Authors

Affiliations

¹ Department of Chemistry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
² National Institute of Polar Research, 10-3, Midori-cho, Tachikawa-shi, Tokyo 190-8518, Japan; Department of Polar Science, The Graduate University for Advanced Studies (SOKENDAI), Shonan Village, Hayama, Kanagawa 240-0193, Japan.
³ National Institute of Polar Research, 10-3, Midori-cho, Tachikawa-shi, Tokyo 190-8518, Japan.
⁴ Faculty of Pure and Applied Sciences and Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan.
⁵ Laboratory for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.
⁶ SUBATECH, IMT Atlantique, CNRS-IN2P3, the University of Nantes, Nantes 44307, France.
⁷ Radiochemistry Unit, Department of Chemistry, The University of Helsinki, Helsinki 00014, Finland.
⁸ Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK.
⁹ Department of Geological Sciences and Center for International Security and Cooperation, Stanford University, Stanford, CA 94305-2115, USA.
¹⁰ Department of Chemistry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan. Electronic address: utsunomiya.satoshi.998@m.kyushu-u.ac.jp.

PMID: 33940743
DOI: 10.1016/j.scitotenv.2021.145639

Abstract

A contaminated zone elongated toward Futaba Town, north-northwest of the Fukushima Daiichi Nuclear Power Plant (FDNPP), contains highly radioactive particles released from reactor Unit 1. There are uncertainties associated with the physio-chemical properties and environmental impacts of these particles. In this study, 31 radioactive particles were isolated from surface soils collected 3.9 km north-northwest of the FDNPP. Two of these particles have the highest particle-associated ^134+137Cs activity ever reported for Fukushima (6.1 × 10⁵ and 2.5 × 10⁶ Bq per particle after decay-correction to March 2011). The new, highly-radioactive particle labeled FTB1 is an aggregate of flaky silicate nanoparticles with an amorphous structure containing ~0.8 wt% Cs, occasionally associated with SiO₂ and TiO₂ inclusions. FTB1 likely originates from the reactor building, which was damaged by a H₂ explosion, after adsorbing volatilized Cs. The ^134+137Cs activity in the other highly radioactive particle labeled FTB26 exceeded 10⁶ Bq. FTB26 has a glassy carbon core and a surface that is embedded with numerous micro-particles: Pb-Sn alloy, fibrous Al-silicate, Ca-carbonate or hydroxide, and quartz. The isotopic signatures of the micro-particles indicate neutron capture by B, Cs volatilization, and adsorption of natural Ba. The composition of the micro-particles on FTB26 reflects the composition of airborne particles at the moment of the H₂ explosion. Owing to their large size, the health effects of the highly radioactive particles are likely limited to external radiation during static contact with skin; the highly radioactive particles are thus expected to have negligible health impacts for humans. By investigating the mobility of the highly radioactive particles, we can better understand how the radiation dose transfers through environments impacted by Unit 1. The highly radioactive particles also provide insights into the atmospheric conditions at the time of the Unit 1 explosion and the physio-chemical phenomena that occurred during reactor meltdown.

Keywords: Boron; Cesium; Fukushima Daiichi Nuclear Power Plant; Isotopic analysis; Radioactive particle; Unit 1.

MeSH terms

Fukushima Nuclear Accident*
Humans
Nuclear Power Plants
Radiation Monitoring*
Radioactivity*
Silicon Dioxide

Substances

Silicon Dioxide