This piece originally appeared at Safecast.

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Image above: Secondary electron images from Utsunomiya et al. 2019, of CsMPs discovered in atmospheric particles trapped on a Tokyo air filter from March 15, 2011, with major constituent elements displayed. Via Safecast

An interesting paper  was recently published by a team headed by Dr. Satoshi Utsunomiya of Kyushu University on the subject of Fukushima-derived cesium-enriched microparticles (CsMPs). As many readers will know, several researchers have located and analyzed these microparticles, in which the cesium is often bonded within glass-like silicates and therefore generally significantly less soluble than other Cs chemical species in water, though technically not actually “insoluble.” After an accident like Fukushima, it is much more common to find cesium in water-soluble compounds like cesium hydroxide (CsOH), and predictions about how quickly the cesium will be dispersed through the environment, in soil, in watersheds, taken up by plants and animals, etc, are based primarily on this assumption. The discovery of sparingly-soluble Fukushima-derived cesium microparticles, first documented by Adachi et al in 2013, and since then confirmed by many others, has raised a number of questions. How abundant are they? Does their presence increase health risk to humans? How much do they reveal about the process of the accident itself? From the standpoint of researchers the microparticles are very intriguing.

Utsunomiya et al.’s paper is titled “Caesium fallout in Tokyo on 15th March, 2011 is dominated by highly radioactive, caesium-rich microparticles,” and as noted in a recent Scientific American article, it was originally accepted for publication in 2017 by Scientific Reports journal. Weeks before publication, however, Tokyo Metropolitan Industrial Technology Research Institute (TIRI), operated by the Tokyo Metropolitan Government, raised objections with Scientific Reports. However no questions about the quality of the science or the validity of the paper’s findings appear to have been brought forward. This in itself was highly irregular. Two years elapsed without resolution, and in March of this year Scientific Reports took the highly unusual step of withdrawing its offer to publish the paper, despite the lack of confirmed evidence that would warrant it. Utsunomiya and several co-authors decided that the best course of action was to place the study in the public domain by publishing it via arXiv, a highly respected pre-print website. The paper is now open and free to download. 

This study makes a valuable contribution to the body of scientific literature regarding the consequences of the Fukushima disaster in general and CsMPs in particular. I think it was a mistake for Scientific Reports not to publish it two years ago, especially considering the rapid pace of research into these particles and the tremendous interest in them. To summarize the findings briefly, the researchers analyzed air filter samples from March 15, 2011, in Setagaya, Tokyo, when the radioactive plume from Fukushima caused a noticeable peak in airborne radioactivity in the city. The researchers used radiographic imaging (placing the filters on a photographic plate) to identify any highly radioactive spots. Using these images as a guide they were able to isolate seven CsMPs, which they subjected to atomic-scale analysis using high-resolution electron microscopy (HRTEM) to identify their nano-scale structure and chemical composition. Based on these detailed measurements and quantitative analysis, the researchers concluded that 80-89% of the total cesium fallout in Tokyo that day was in the form of highly radioactive microparticles. The second half of the paper is devoted to estimates of how long such particles might be retained in the human lungs if inhaled, based on previous studies that reported the effects of inhalation of non-radioactive atmospheric particles, and some possible physical consequences. The paper is valuable for the quantitative analysis of the Tokyo particles alone, since it is one of few studies that deal with the issue for Tokyo specifically. Research into possible health consequences of the particles, meanwhile, has gained momentum while the paper remained unpublished, using approaches such as stochastic biokinetics, and DNA damage studies.  In a recent paper, Utsunomiya and colleagues produced estimates of the rate of dissolution of the particles inside the human lung, in pure water, and in seawater. A working group at the Japan Health Physics Society has also devoted attention to the issue, noting the need for further study of the risk from intake of these particles, particularly to the lung.  Likewise, others have been studying the particles to learn about the accident progression and possible consequences for decommissioning.

Why did Tokyo Metropolitan Industrial Technology Research Institute object to the paper’s publication? When we first heard that publication of the paper was being held up by Tokyo Metropolitan Government, we thought politically-motivated suppression was a likely explanation. Since then the public has learned that the actual complaint given to Scientific Reports stems from a chain of custody issue of the original air filter samples. We don’t want to speculate further about Tokyo’s motivation, because we have seen no direct evidence yet of political suppression in this case. But based on past occurrences with other government institutions, we would find it plausible. We will let readers know if TIRI responds to our inquiries.

We spoke with Dr. Utsunomiya and co-author Dr. Rodney Ewing recently. I was aware of their co-authorship of several strong papers on CsMPs, including Utsunomiya’s plenary talk at the Goldschmidt Conference in Yokohama in 2016, which I attended. I asked how this new arXiv paper fits in with their other papers, and where they think this research is heading next:

Satoshi Utsunomiya:

Thank you for asking. The Tokyo paper was actually our first paper regarding CsMPs. As I mentioned, the paper was accepted two years ago. There were no previous papers of ours on CsMPs that time. Currently we are working on several topics on CsMPs. I cannot reveal the content yet, as we are thinking about a press release for the next paper. But I think it is important to continue this kind of research, providing some insights for decommissioning at Fukushima Daiichi Nuclear Power Plant.

Azby Brown:

I didn’t realize that this was your first paper on the subject.  How does it relate to the one presented at the Goldschmidt Conference in Yokohama in 2016? “Cesium-Rich Micro-Particles Unveil the Explosive Events in the Fukushima Daiichi Nuclear Power Plant.” Didn’t that paper receive a prize?

SU:

My talk at Goldschmidt briefly covered the story described in the two papers that were accepted for publication at the same time. One was published in Scientific Reports. The other one was not published. There was no prize. It was a plenary talk.

AB:

I see. I recall that it received a lot of attention. Now it makes more sense to me.

Can you tell me a little bit about the specific characteristics and focus of your research, and how it differs from papers like Adachi 2013, Abe 2014, etc? Generally speaking, that is. I’d like to help people understand the different aspects of the field.

SU:

Adachi reported the discovery of CsMPs. Abe demonstrated X-ray absorption analysis on the CsMPs. We focused on the nanotexture inside CsMPs. We are particularly interested in the detailed evidence remaining within the microparticle, which can provide useful information on the development of the chemical reactions during the meltdowns, because it is still difficult to directly analyze the materials inside the reactors. We, for the first time, succeeded in performing isotopic analysis on individual CsMPs. More specifically, the occurrence of uranium can directly tell the story of how the fuel melted. Our research has two directions: one is to understand the environmental impact of CsMPs, and the other is to provide useful information on the debris properties to help decommissioning at FDNPP. We are also interested in the implications for health.

AB:

Can you tell me a little bit about your working relationship? Satoshi went to the US to work in your lab, right Rod? When was that, and what were you working on?

Rod Ewing:

Satoshi and I have known each other since 2000, when he joined my research group as a post-doctoral fellow at the University of Michigan. He was a member of the research group until 2007. We collaborated on a wide range of topics that had to do with radioactive materials, such as the transport of plutonium at the Mayak site in Russia to the identification of uranium phases within C60 cages, so called buckyballs, that were formed and released from coal power plants. Once Satoshi returned to Japan to take his position at Kyushu University, we continued to collaborate, particularly on topics related to Fukushima Daiichi.

AB:

How did you both get interested in CsMPs?

RE:

Once discovered, CsMPs were clearly of high interest. They had not been noted in earlier reactor accidents. Satoshi is a master with the transmission electron microscope – exactly the tool/technique needed to study these particles.

AB:

For people who aren’t familiar with what’s involved in a research experiment like yours, can you describe the overall process? What were the technical challenges?

RE:

I would just emphasize that it is very difficult to find and characterize these particles. Considering the full literature and efforts by others as well as our team – the results are impressive. It is rare to have both the TEM characterization and the isotopic data.

SU:

As Rod mentioned, it is difficult to obtain both TEM and isotopic data from a few micron-sized spots. The isolation of CsMPs from soils is a time consuming process. But to date, many scientists have found and isolated CsMPs. The important thing is what information we can obtain from the analysis of CsMPs. We have been taking various approaches to elucidate the properties, environmental impact, and the role in releasing fissile actinides to the environment.    

As described above, many papers examining various aspects of Fukushima-derived cesium microparticles have been published since they were first identified in 2013. Even so, important aspects remain only partially documented and understood to date. Below is a partial list of relevant publications.

Papers mentioned in this article:

Caesium fallout in Tokyo on 15th March, 2011 is dominated by highly radioactive, caesium-rich microparticles

Utsunomiya, et al., 2019

https://arxiv.org/abs/1906.00212

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

Adachi et al., 2013

http://www.nature.com/articles/srep02554

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Detection of Uranium and Chemical State Analysis of Individual Radioactive Microparticles Emitted from the Fukushima Nuclear Accident Using Multiple Synchrotron Radiation X-ray Analyses

Abe et al., 2014

http://pubs.acs.org/doi/abs/10.1021/ac501998d

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Dissolution of radioactive, cesium-rich microparticles released from the Fukushima Daiichi Nuclear Power Plant in simulated lung fluid, pure-water, and seawater

Suetake et al., 2019

https://doi.org/10.1016/j.chemosphere.2019.05.248

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Development of a stochastic biokinetic method and its application to internal dose estimation for insoluble cesium-bearing particles

Manabe & Matsumoto, 2019

https://doi.org/10.1080/00223131.2018.1523756

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DNA damage induction during localized chronic exposure to an insoluble radioactive microparticle

Matsuya et al., 2019

https://doi.org/10.1038/s41598-019-46874-6

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Provenance of uranium particulate contained within Fukushima Daiichi Nuclear Power Plant Unit 1 ejecta material

Martin et al., 2019

https://www.nature.com/articles/s41467-019-10937-z

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Internal doses from radionuclides and their health effects following the Fukushima accident

Ishikawa et al., 2018

https://iopscience.iop.org/article/10.1088/1361-6498/aadb4c

Related papers (by year of publication):

Characteristics Of Spherical Cs-Bearing Particles Collected During The Early Stage Of FDNPP Accident

Igarashi et al., 2014

http://www-pub.iaea.org/iaeameetings/cn224p/Session3/Igarashi.pdf

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Radioactive Cs in the severely contaminated soils near the Fukushima Daiichi nuclear power plant

Kaneko et al., 2015

https://www.frontiersin.org/articles/10.3389/fenrg.2015.00037

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First successful isolation of radioactive particles from soil near the Fukushima Daiichi Nuclear Power Plant

Satou et al., 2016

http://www.sciencedirect.com/science/article/pii/S2213305416300340

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Internal structure of cesium-bearing radioactive microparticles released from Fukushima nuclear power plant

Yamaguchi et al., 2016

http://www.nature.com/articles/srep20548

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Three-Year Retention Of Radioactive Caesium In The Body Of Tepco Workers Involved In The Fukushima Daiichi Nuclear Power Station Accident

Nakano et al., 2016

http://rpd.oxfordjournals.org/content/early/2016/03/14/rpd.ncw036

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Monte Carlo Evaluation of Internal Dose and Distribution Imaging Due to Insoluble Radioactive Cs-Bearing Particles of Water Deposited Inside Lungs via Pulmonary Inhalation Using PHITS Code Combined with Voxel Phantom Data

Sakama, M. et al., 2016

https://link.springer.com/chapter/10.1007/978-4-431-55848-4_19

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Radioactively-hot particles detected in dusts and soils from Northern Japan by combination of gamma spectrometry, autoradiography, and SEM/EDS analysis and implications in radiation risk assessment

Kaltofen & Gundersen, 2017

https://www.sciencedirect.com/science/article/pii/S0048969717317953?via%3Dihub

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Caesium-rich micro-particles: A window into the meltdown events at the Fukushima Daiichi Nuclear Power Plant

Furuki et al., 2017

https://www.nature.com/articles/srep42731

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Isotopic signature and nano-texture of cesium-rich micro-particles: Release of uranium and fission products from the Fukushima Daiichi Nuclear Power Plant

Imoto et al., 2017

https://www.nature.com/articles/s41598-017-05910-z

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Uranium dioxides and debris fragments released to the environment with cesium-rich microparticles from the Fukushima Daiichi Nuclear Power Plant

Ochiai et al., 2018

https://pubs.acs.org/doi/abs/10.1021/acs.est.7b06309

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Novel method of quantifying radioactive cesium-rich microparticles (CsMPs) in the environment from the Fukushima Daiichi nuclear power plant

Ikehara et al., 2018

https://pubs.acs.org/doi/full/10.1021/acs.est.7b06693

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Formation of radioactive cesium microparticles originating from the Fukushima Daiichi Nuclear Power Plant accident: characteristics and perspectives

Ohnuki, Satou, and Utsunomiya, 2019

https://www.tandfonline.com/doi/abs/10.1080/00223131.2019.1595767

This piece originally appeared in the Bulletin of the Atomic Scientists.

As we witness the increasingly detrimental effects of global climate change, the role that nuclear power could play globally to mitigate its effects continues to be debated. The series of articles featured in the Bulletin in December 2016 aired a broad spectrum of opinions, ranging in assessment of the role of nuclear power from insignificant to mandatory. In this series, we present the perspective of a new crop of nuclear professionals who collectively represent two of the world leaders in nuclear power—the United States and Russia.

These young professionals work together to exchange views and ideas as part of the U.S.-Russia Young Professionals Nuclear Forum that we created in May 2016 to encourage dialogue on critical nuclear issues of concern to both countries. As most official avenues of US-Russia cooperation on nuclear issues were being shut down in pace with the deteriorating political relations between Washington and Moscow, our objective was to turn to the younger generation, because those in it will have to live with the consequences of a world in which their countries no longer cooperate to mitigate global nuclear dangers.

In the United States, our efforts are organized within the Center for International Security and Cooperation at Stanford University, although we reach out to universities and other organizations across the country. In Russia, we were fortunate to find the Moscow Engineering Physics Institute (MEPhI), Russia’s flagship research university in nuclear engineering, to be an enthusiastic partner. Its rector, Professor Mikhail Strikhanov, has an unwavering international outlook that stresses the need for cooperation, especially in higher education and research. The young professionals are students, postdoctoral fellows, and early career professionals.

Hecker has previously written in the Bulletin about the remarkable period of post-Cold War nuclear cooperation between Russian and American nuclear weapon scientists and how the termination of that cooperation by our governments threatens our collective security. We viewed engaging young professionals from the two countries as one of the few avenues of continued cooperation. It has the potential of being particularly effective because at the forum meetings, the young Russians and Americans interact in an educational and non-adversarial environment.

The first three forum meetings focused primarily on issues of nuclear non-proliferation and countering nuclear terrorism. They featured exercises in which the young professionals worked in small groups side by side to explore solutions to vexing nuclear problems. One was a simulation conducted at Stanford in May 2018 just a few weeks before the historic Trump-Kim Singapore Summit. The other was an exercise in Moscow in October 2018 to advise their governments on a hypothetical crisis related to the US withdrawal from the Iran nuclear deal.

At the Moscow forum, we also asked the young professionals to explore what the two countries could do to promote the benefits of nuclear energy around the globe, while cooperating to mitigate the associated risks.

Preparation for the forum included online lectures by senior mentors as well as lectures and discussion sessions in Moscow by both Russian and American specialists. In the nuclear power exercise, we assigned eight key questions to 24 young professionals. We divided them into eight teams, each composed of Russian and American participants. The central question was whether or not an expansion of global nuclear power is necessary to help mitigate the danger of global climate change. Individual groups examined issues of supply and demand around the globe and some of the big challenges posed by an expansion of nuclear power—those of economics, safety and security, potential proliferation of nuclear weapons, and the disposition of nuclear waste.

The young professionals conducted research prior to the meeting, deliberated and debated within their teams during the meeting, and presented their findings to the larger group and the panel of senior mentors at the end of the exercise. During the past six months they have captured the essence of their findings in the eight articles featured in this special presentation in the Bulletin.

Their findings are generally pro-nuclear, which is not surprising considering that most of them have strong educational and research backgrounds in either nuclear technologies or nuclear security. But we found that their views were primarily driven by their serious concerns about the dangers of global climate change and the urgent need to confront these dangers.

Their articles are of interest not so much in that they break new ground in these areas, particularly since many other  established experts have tried to tackle these issues for decades. They are of interest because they represent the views of some of the younger generation of professionals working together across cultural and disciplinary divides. We were struck by the following comment in one of the papers  that reflects on the perceived urgency of the task at hand: “We are the first generation that is experiencing the dramatic effects of global climate change and likely the last that can do something about it to avoid catastrophic consequences for the Earth and its people.”

We also note that the articles uniformly reveal that the young professionals across the board firmly believe that the benefits and risks of expanding nuclear power globally must be pursued and tackled in a concerted effort of major nuclear powers (especially the United States and Russia), other developed nations, the International Atomic Energy Agency, and all stakeholders. These younger voices stated: “The most important shift necessary to facilitate [nuclear power] expansion is an increase in international cooperation and multilateralization in the form of, for example, international reactor supply contracts, multinational enrichment conglomerates, nondiscriminatory fuel banks, and international waste repositories.”

We believe the readers will find the sentiments and opinions of the young Russian and American professionals interesting and encouraging. We certainly have found them eager and able to work together effectively—a lesson that the more senior professionals and the governments need to relearn.

Editor’s note: The Young Professionals Nuclear Forum cooperation is supported by the John D. and Catherine T. MacArthur Foundation and the Carnegie Corporation of New York.

Read the articles here:

• Nuclear Power and Global Climate Change
• What Countries Will Be the Most Important in Leading a Significant Expansion of Global Nuclear Power—Both From the Perspective of the Supplier and the User?
• Should Nuclear Power Be Expanded Significantly Into Developing Countries?
• What Will Be Required for a Significant Expansion of Global Nuclear Energy?
• Resolving Safety and Security Concerns About Nuclear Power
• Why Nuclear Power Plants Cost so Much—and What Can Be Done About It
• Will Nuclear Waste Disposal Challenges Limit a Significant Expansion of Global Nuclear Power? Part 1
• Will Nuclear Waste Disposal Challenges Limit a Significant Expansion of Global Nuclear Power? Part 2

In early May, CISAC convened the fifth Young Professional Nuclear Forum (YPNF), a program sponsored by the Center for International Security and Cooperation at Stanford University and the Moscow Engineering and Physics Institute (MEPhI). The program brought together a lively group of young Russians and Americans working on nuclear issues over three days.

Since 2016, the forum has alternated between Moscow and Stanford.  

By 2016, US and Russian governments closed almost every door on opportunities that previously allowed experienced nuclear professionals on both sides to cooperate with each other.  Stanford Professor Siegfried Hecker saw that at least one door - that of cooperation on the university level - was still open. He started the YPNF to foster interaction between the younger generation of Russians and Americans who study, do research, or start a career in the nuclear power or nonproliferation fields.

This year’s agenda focused on two major areas: US-Russian arms control and the future of nuclear power.

The American group included a new cohort of six incoming young professionals from Los Alamos National Laboratory, UC Berkeley, Center for Arms Control and Non-Proliferation, and Vienna Center for Disarmament and Non‑Proliferation. They were joined by CISAC research staff members Gaby Levikow and Elliot Serbin and current and former fellows Chantell Murphy, Kristin Ven Bruusgaard, and Cameron Tracy. The Russian group from MEPhI brought a team of 12 young professionals most of whom are pursuing their graduate degrees in nuclear physics and engineering and software engineering, along with junior professionals in international relations and nuclear fields.  The team of experts included Professor Hecker, Dr. James Toevs, Dr. Ning Li, Ambassador Steven Pifer, Professor David Holloway, Dr. Larry Brandt, Dr. Chaim Braun, Dr. Pavel Podvig, and Dr. Mona Dreicer, —all of whom provided advice and feedback during the exercise.

Participants come from loosely defined “technical” and “policy” fields, and the forum agenda has traditionally included one nuclear-power related and one policy-focused subject. Forum activities vary between lectures, expert briefings, discussions, and table-top exercises, but the small-group work during the exercises is the core form of interaction.

By design, this agenda exposes each participant to new fields, new counterparts, some fun interactive time off - and encourages a lot of cultural learning. Forum after forum, we hear back that the group work and social time are the most exciting aspects of the forum experience. Participants noted they learned, among other things, “general ideas and thoughts of American participants and their attitudes to the present American policy, new words and abbreviations … [and] a great deal about new reactor designs and their implications for nuclear energy and security policy.”  Still more participants enjoyed “learning to collaborate in groups of Americans and Russians but also between policy and technical experts on topics of both camps,” and some “got new friends.”

Encouragingly, participants requested more interaction between the bi-annual meetings and a variety of topics in yet untapped – or suspended - areas of cooperation between Russia and the US.

New work continues to emerge from the forum. Eight short articles written by the young professionals to showcase the results of the projects from the Moscow meeting in November 2017 was published in the Bulletin of the Atomic Scientists in June 2019. The next meeting will be held in Moscow this November.

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.