title: Caesium-rich micro-particles: A window into the meltdown events at the Fukushima Daiichi Nuclear Power Plant.
abstract: The nuclear disaster at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March 2011 caused partial meltdowns of three reactors. During the meltdowns, a type of condensed particle, a caesium-rich micro-particle (CsMP), formed inside the reactors via unknown processes. Here we report the chemical and physical processes of CsMP formation inside the reactors during the meltdowns based on atomic-resolution electron microscopy of CsMPs discovered near the FDNPP. All of the CsMPs (with sizes of 2.0-3.4 μm) comprise SiO2glass matrices and ~10-nm-sized Zn-Fe-oxide nanoparticles associated with a wide range of Cs concentrations (1.1-19 wt% Cs as Cs2O). Trace amounts of U are also associated with the Zn-Fe oxides. The nano-texture in the CsMPs records multiple reaction-process steps during meltdown in the severe FDNPP accident: Melted fuel (molten core)-concrete interactions (MCCIs), incorporating various airborne fission product nanoparticles, including CsOH and CsCl, proceeded via SiO2condensation over aggregates of Zn-Fe oxide nanoparticles originating from the failure of the reactor pressure vessels. Still, CsMPs provide a mechanism by which volatile and low-volatility radionuclides such as U can reach the environment and should be considered in the migration model of Cs and radionuclides in the current environment surrounding the FDNPP.
authors.affiliation: Department of Chemistry, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Genki
authors.initials: G
authors.lastname: Furuki
authors.affiliation: Department of Chemistry, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Junpei
authors.initials: J
authors.lastname: Imoto
authors.affiliation: Department of Chemistry, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Asumi
authors.initials: A
authors.lastname: Ochiai
authors.affiliation: 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.
authors.forename: Shinya
authors.initials: S
authors.lastname: Yamasaki
authors.affiliation: Department of Environmental Management, Faculty of Symbiotic System Science, Fukushima University, Kanayagawa 1, Fukushima, 960-1296 Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Nanba
authors.affiliation: Laboratory for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ohnuki
authors.affiliation: SUBATECH, IMT Atlantique, Université de Nantes, CNRS/IN2P3, Nantes 44307, France.
authors.forename: Bernd
authors.initials: B
authors.lastname: Grambow
authors.affiliation: Department of Geological Sciences and Center for International Security and Cooperation, Stanford University, Stanford, CA 94305-2115 USA.
authors.forename: Rodney C
authors.initials: RC
authors.lastname: Ewing
authors.affiliation: Department of Chemistry, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Utsunomiya