In March 2011, a post-earthquake tsunami triggered nuclear meltdowns, hydrogen-air explosions and the release of radioactive materials from the Fukushima Daiichi Nuclear Power Plant in Fukushima Prefecture, Japan. The Fukushima disaster has been called the most significant nuclear incident since the 1986 Chernobyl disaster. Professor Rodney C. Ewing, Frank Stanton Professor in Nuclear Security and co-director at the Center for International Security and Cooperation (CISAC) in the Freeman Spogli Institute for International Studies (FSI), as a member of a team of Japanese researchers, today published a report on the details of what exactly — at the particle level — was released into the air after the disaster.
In the discussion that follows, Ewing explains the team’s findings and why they are important for health and environmental safety.
Why did you decide to study the Fukushima disaster?
The Fukishima Daiichi event surprised me. I now teach a freshman seminar on this event. I am particularly interested to understand why the accident occurred and what the long-term impact will be on the environment. This research paper reflects my interest in answering these questions.
We’ve heard lots about possible health effects from contaminated water after the Fukushima disaster, but less about particulates in the air. What did you find?
During the core melt-down events at Fukushima Daiichi, radioactivity was released as fine particulates that traveled in the air, sometime for distances of tens of kilometers, and settled onto the surrounding countryside.
In order to understand the health risk, it is very important to understand the form and chemistry of these particulates.
Recently, in a previous paper we have described a new type of particulate that is Cs-rich (some Cs isotopes are highly radioactive). The highly radioactive Cs-rich particles formed in the reactor by condensation from a silica-rich vapor, formed from the melting of core and concrete structures. In this paper, we describe the first identification of fragments of the melted core that were entrapped by the Cs-particles and transported away from the reactor site, some 4 kilometers. This is an important discovery because this provides us with samples of the fuel and melted core.
This is a special contribution because it uses very advanced electron microscopy techniques that allow for imaging of individual atoms or clusters of atoms. This advanced technique is required because the particles are so small — nanometers in size.
How did you come to work with your collaborators in Japan?
I have had long standing collaborations with Japanese scientists for decades. The lead researcher for the group, Professor Satoshi Utusunomiya, was once a member of my research group when I was at the University of Michigan. We have always collaborated on topics that involve radioactive materials and the use of electron microscopy. This collaboration is an entirely natural outgrowth of previous collaborations.
What, if any, policy recommendations would you suggest based on your findings?
The most direct result would be to design monitoring systems so that we have a good record of released particulates. Also, we need to push the development of advanced analytical techniques so that these particulates can be quickly identified and characterized.