Q&A with 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). Interview with Katy Gabel Chui.

Your previous research with this team helped identify the types of radioactive particles that can become airborne and were transported away from Fukushima during the 2011 nuclear disaster.

This most recent paper goes further to show how these Cesium (Cs)-rich silica particles behave in several types of fluids, including simulated human lung fluid, concluding that the particles are fully dissolved in the latter after more than 35 years. What might that mean for human health in the Fukushima area and beyond?

The first breakthrough was the recognition that such particles, a few microns in diameter, existed, a discovery by Japanese scientists at the Meteorological Research Institute, Tsukuba, in 2013. The particles are important because they were dispersed over distances of tens of kilometers and were “carriers” of highly radioactive Cs. Our team’s previous work, led by Professor Satoshi Utsunomiya, mainly focused on the characterization of the particles and their constituents at the atomic-scale and surveyed their distribution in the area away from the Fukushima Daiichi nuclear power plants. Our earliest work from 2016 can be found online. A good summary of the history of the work on these cesium-rich microparticles was recently published in Scientific American.

This latest paper published in Chemosphere is the 6th in a series of papers on the Cs-rich microparticles. We describe the behavior of these particles when exposed to different types of fluids: ultra-pure water, artificial sea water and simulated lung fluid. The microparticles dissolve in all three fluids, reaching a long-term but a continuing, slow rate of release after just three days. Essentially, the calculated release rate of cesium depends on the rate of dissolution of the silica glass matrix and the initial size of the particles. In the simulated lung fluid, the particles are modelled to fully dissolve after more than 35 years.

What is the simulated lung fluid made of, and how does it work in simulation? How do you estimate 35 years?

The constituents of typical lung fluid were simply mixed to simulate its composition based on a recipe reported by previous studies. The lung fluid is different from the other solutions because it contains organic compounds and has a different chemistry, i.e., higher sodium and chlorine content. The estimates of residence time in the body assumes that the particles are inhaled and find their way to the pulmonary system. The calculation of residence time is based on assumptions about the size and composition of the microparticles, and we used the long-term release rate from the experiments. We assumed a spherical shape and a constant decrease in size as the leaching process continued. The rate can vary depending on the actual shape, internal texture, composition (such as occurrence of intrinsic Cs-phase inclusions), and precipitation of secondary phases that may form a “protective” coating on the cesium-rich microparticles (CsMPs). The rate of release was fastest in the simulated lung fluid.

The important result is to realize that the Cs-rich silica particles dissolve slowly in the environment and in the body. Essentially, the release extends for several decades.

How can nuclear energy experts and policy makers use this research to avoid future risk?

Understanding the form and composition of materials that host and disperse radionuclides is the first step in completing a careful dose calculation. Based on these results, the fraction of Cs contained in the silica particles will not be rapidly “flushed” through the environment or the body, but rather will be released over several decades.

Thousands of tons of highly radioactive spent fuel are in temporary storage in 35 states, with no permanent solution being discussed. International experts led by Stanford show how to end this status quo.

Rod Ewing led a three-year study recommending changes to the U.S. nuclear waste management program. (Image credit: Courtesy CISAC)

The U.S. government has worked for decades and spent tens of billions of dollars in search of a permanent resting place for the nation’s nuclear waste. Some 80,000 tons of highly radioactive spent fuel from commercial nuclear power plants and millions of gallons of high-level nuclear waste from defense programs are stored in pools, dry casks and large tanks at more than 75 sites throughout the country.

A Stanford University-led study recommends that the United States reset its nuclear waste program by moving responsibility for commercially generated, used nuclear fuel away from the federal government and into the hands of an independent, nonprofit, utility-owned and -funded nuclear waste management organization.

“No single group, institution or governmental organization is incentivized to find a solution,” said Rod Ewing, co-director of Stanford’s Center for International Security and Cooperation and a professor of geological sciences.

The three-year study, led by Ewing, makes a series of recommendations focused on the back-end of the nuclear fuel cycle. The report, Reset of America’s Nuclear Waste Management Strategy and Policy, was released today.

A tightening knot

Over the past four decades, the U.S. nuclear waste program has suffered from continuing changes to the original Nuclear Waste Policy Act, a slow-to-develop and changing regulatory framework. Erratic funding, significant changes in policy with changing administrations, conflicting policies from Congress and the executive branch and – most important – inadequate public engagement have also blocked any progress.

“The U.S. program is in an ever-tightening Gordian knot – the strands of which are technical, logistical, regulatory, legal, financial, social and political – all caught in a web of agreements with states and communities, regulations, court rulings and the congressional budgetary process,” the report says.

The project’s steering committee sought to untangle these technical, administrative and public barriers so that critical issues could be identified and overcome. They held five open meetings with some 75 internationally recognized experts, government officials, leaders of nongovernmental organizations, affected citizens and Stanford scholars as speakers.

After describing the Sisyphean history of the U.S. nuclear waste management and disposal program, the report makes recommendations all focused around a final goal: long-term disposal of highly radioactive waste in a mined, geologic repository.

“Most importantly, the United States has taken its eyes off the prize, that is, disposal of highly radioactive nuclear waste in a deep-mined geologic repository,” said Allison Macfarlane, a member of the steering committee and a professor of public policy and international affairs at George Washington University. “Spent nuclear fuel stored above ground – either in pools or dry casks – is not a solution. These facilities will eventually degrade. And, if not monitored and cared for, they will contaminate our environment.”

Not a new idea abroad

The new, independent, utility-owned organization would control spent fuel from the time it is removed from reactors until its final disposal in a geologic repository. This is not a new idea. Finland, Sweden, Switzerland and Canada all have adopted a similar approach – and their nuclear waste management programs are moving forward. Finland expects to receive its first spent fuel at its geologic repository on the island of Olkiluoto in the mid-2020s.

“Initially, I was skeptical about placing utilities with nuclear power plants in control of the spent fuel from commercial reactors,” said Ewing. “But as we discussed the advantages of this cradle-to-grave approach, I was persuaded, particularly because this is the approach taken by other successful programs.”

Essential to the success of a new organization would be access to the Nuclear Waste Fund. Reassigning responsibility to a new organization – whether controlled by the federal government or nuclear utilities – would require an act of Congress. The report recommends that the Nuclear Waste Fund, more than $40 billion, be transferred to the new organization over several decades. If the new organization successfully develops a geologic repository, this repository could also be used for highly radioactive defense waste.

“The status quo is a big liability for the future of nuclear power, an established source of carbon-free electricity,” said Sally Benson, co-director of Stanford’s Precourt Institute for Energy and a member of the report’s steering committee. “These recommendations will, I hope, break the gridlock in Washington and prompt concrete action to solve this problem.”

To read all stories about Stanford science, subscribe to the biweekly Stanford Science Digest.

Benson is also a professor of energy resources engineering. She and Ewing are members of Stanford’s School of Earth, Energy & Environmental Sciences.

The Reset of America’s Nuclear Waste Management project was funded by the Precourt Institute for Energy, the Freeman Spogli Institute for International Studies and the Center for International Security and Cooperation. The meetings at George Washington University were supported by the John D. & Catherine T. MacArthur Foundation.