A single radioactive cloud was likely responsible for dispersing highly radioactive microscopic particles across large parts of Fukushima Prefecture during the Fukushima Daiichi nuclear disaster. The finding helps us understand the dispersion of radioactive materials after the accident.
A that a single radioactive cloud was responsible for a large share of the nuclear fallout during the Fukushima Daiichi nuclear disaster on 11 March 2011.
The accident released radioactive cesium around the power plant. While most of the cesium dissolved and bound into soils, some cesium took the form of cesium-rich microparticles (CsMPs). These particles, while tiny and insoluble, can carry extremely high radioactivity per unit mass.
By analysing 100 environmental samples collected within several months after the accident, the researchers found that CsMPs are unevenly distributed and do not follow the same patterns as total radioactive fallout. Instead of being spread evenly in the vicinity of the accident, CsMPs were picked up by a single gust of wind and transported across Fukushima Prefecture only on 15 March, 2011.
"This study shows that much of the particulate contamination across Fukushima can be traced back to a single release event," says Professor Satoshi Utsunomiya from the National Taiwan University.
"It fundamentally changes how we understand the dispersion of radioactive materials after the Fukushima Daiichi accident."
Rainfall determined particle contamination pattern
The study also shows that precipitation, not just release magnitude, controlled where CsMPs accumulated.
"When a particle-rich plume met rainfall, the particles were rapidly scavenged from the atmosphere," says Professor from the University of Helsinki.
"As a result, the distribution of these particles reflects weather conditions as much as the release timing itself." Because CsMPs are highly radioactive and behave differently from soluble contaminants, they may represent an additional environmental and health risk.
"These particles persist in the environment and have the potential to deliver highly localised radiation doses if consumed or inhaled," says Bernd Grambow from IMT Atlantique.
"Understanding their distribution is essential for long-term risk assessment and remediation."
The team is now focusing on the potential health impacts of inhaling these particles, building on evidence that they may cause enhanced biological damage compared to more diffuse forms of ionic radio-Cs contamination.
The study was carried out by an international team, including scientists from the National Taiwan University, the University of Helsinki and the University of Nantes/IMT Atlantique/CNRS.
The work was supported by Ministry of Education, National Science and Technology Council, Taiwan, the Japan Society for the Promotion of Science and the Research Council of Finland.
