The Fukushima Daiichi Nuclear Power Plant released particles containing radioactive cesium during the 2011 nuclear disaster. New research published in Science of the Total Environment shows that some particles were larger and contained much higher levels of activity than was previously known.
“This paper is part of a series of publications that provide a detailed picture of the material emitted during the Fukushima Daiichi reactor meltdowns,” said CISAC Co-Director Rod Ewing, the Frank Stanton Professor in Nuclear Security who collaborated with scholars from Japan, Finland, France, and the United Kingdom on this research.
“This is exactly the type of work required for remediation and an understanding of long-term health effects,” Ewing said.
The larger particles were found during a survey of surface soils 3.9 km north-northwest of reactor unit 1. Two of the 31 Cs-particles collected during the sampling campaign have given the highest ever particle-associated 134+137Cs activities for materials emitted from the Fukushima Daiichi Nuclear Power Plant (FDNPP).
The researchers used a combination of advanced analytical techniques (synchrotron-based nano-focus X-ray analysis, secondary ion mass spectrometry, and high-resolution transmission electron microscopy) to fully characterize the particles.
One particle, which was found to be an aggregate of smaller, “flakey” silicate nanoparticles, with a glass-like structure likely came from reactor building materials, which were damaged during the Unit 1 hydrogen explosion; then, as the particle formed, it likely adsorbed Cs that had had been volatized from the hot reactor fuel. The composition of the surface embedded micro-particles likely reflects the composition of airborne particles within the reactor building at the moment of the hydrogen explosion, thus providing a forensic window into the events of March 11, 2011.
Dr. Satoshi Utsunomiya at the University of Kyushu led the study. “The new particles from regions close to the damaged reactor provide valuable forensic clues,” he said. “They give snap-shots of the atmospheric conditions in the reactor building at the time of the hydrogen explosion and of the physio-chemical phenomena that occurred during reactor meltdown.”
“While ten years have passed since the accident, the importance of scientific insights has never been more critical,” Utsunomiya said. “Clean-up and repatriation of residents continues and a thorough understanding of the contamination forms and their distribution is important for risk assessment and public trust.”
Gareth Law at the University of Helsinki who worked on the study, said that ongoing clean-up and decommissioning efforts at the site face difficult challenges, particularly the removal and safe management of accident debris with very high levels of radioactivity. “Prior knowledge of debris composition can help inform safe management approaches,” he said.
Given the high radioactivity associated with the new particles, the project team was also interested in understanding their potential health and dose impacts. “Owing to their large size, the health effects of the new particles are likely limited to external radiation hazards during static contact with skin,” Utsunomiya said. “As such, despite the very high level of activity, we expect that the particles would have negligible health impacts for humans as they would not easily adhere to the skin. However, we do need to consider possible effects on the other living creatures such as filter feeders in habitats surrounding Fukushima Daiichi. Even though ten years have already passed, the half-life of 137Cs is ~30 years. So, the activity in the newly found highly radioactive particles has not yet decayed significantly. As such, they will remain in the environment for many decades to come, and this type of particle could occasionally still be found in radiation hot spots.”
Bernd Grambow, Chair of the Nuclear Waste Management at IMT Atlantique, said, “The present work, using cutting-edge analytical tools, gives only a very small insight in the very large diversity of particles released during the nuclear accident, much more work is necessary to get a realistic picture of the highly heterogeneous environmental and health impact.”
Q&A with Rodney C. Ewing, co-director of the Center for International Security and Cooperation and a senior fellow at the Freeman Spogli Institute for International Studies. This story first appeared in Medium.