Emission of spherical cesium-bearing particles from an early stage of the Fukushima nuclear accident

TLDR

The Fukushima nuclear accident released radioactive materials worldwide in March 2011, yet their exact physical and chemical properties remain unknown, prompting extensive cleanup efforts. This study directly observed spherical cesium‑bearing particles emitted on March 14–15 and, through simulation, showed they mainly deposited on the ground by dry deposition. These particles are larger, contain Fe, Zn, and Cs, are water‑insoluble, and their discovery is crucial for understanding the accident’s processes, assessing health impacts, and estimating environmental residence time.

Abstract

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.