Few scientific fields display more breadth and depth than nuclear materials—a topic that deals with almost everything that touches on nuclear reactions. Scientists coming from many diverse disciplines work with nuclear materials: Physicists explore the neutron economy of reactors to develop new reactor designs and advanced nuclear fuel cycles. Materials scientists develop new nuclear fuels for reactors and waste forms to immobilize radionuclides in repositories. Radiochemists study the effects of radiation on minerals and the corrosion of nuclear materials in contact with water. Nuclear engineers develop new reactor safety systems and containment methods for geological repositories of nuclear waste. Geoscientists estimate the long-term behavior of host rocks and the hydrology of repositories. Geochemists study the fate of plutonium, uranium, and other radioactive materials in the environment after nuclear reactor accidents or breaches of nuclear waste packages in repositories. Health scientists study the impacts of radiative materials on humans and animals. Social scientists and philosophers discuss the issues of trust, risk, and ethics associated with managing nuclear waste materials and nuclear facilities and the complicated relationship between science and safety.

These are all issues of great scientific and public value. They were also the very topics—as he called them, his “hobbies”—that Rod Ewing was most interested in.

Rodney C. Ewing (1946-2024) was a professor in nuclear security and a professor in geosciences at Stanford University and a professor emeritus at the University of Michigan and the University of New Mexico. He was a fellow of the National Academy of Engineering since 2017, and a longtime member of the Bulletin’s Science and Security Board. Ewing passed away in July at the age of 77.

Throughout his career of nearly 50 years, Ewing—a mineralogist turned material engineer—became arguably the world’s top expert on nuclear materials (Hecker, Park, and Tracy, 2024). He was also a great mentor and friend to a whole generation of scientists and scholars (including me) involved in the science and policy issues of nuclear materials. To pay tribute to Rod’s many contributions to the field, this issue of the Bulletin brings together some of his former collaborators to explore the enduring risks and new challenges of nuclear materials.

In their piece, “Glass and ceramic nuclear waste forms: the scientific battle,” Daniel J. Gregg and his colleagues tell the story of the scientific battle between two major classes of materials to be the best option for immobilization and disposal of high-level nuclear waste—a battle that has played out since the 1970s. They also highlight some of Rod’s essential contributions in the areas of radiation damage and nuclear waste forms.

In an investigative science reporting piece, “How Fukushima’s radioactive fallout in Tokyo was concealed from the public,” I reveal how very high concentrations of insoluble cesium microparticles were found in Tokyo following the Fukushima nuclear plant accident in March 2011, and how these findings were kept from the public’s eye for years.

In his essay, “Becoming a responsible ancestor,” Daniel Metlay discusses how the United States, which possesses the largest inventory of high-level radioactive waste and spent nuclear fuel in the world, still has no plan to permanently dispose of these materials. He also explains how the legal framework for US nuclear waste management might be reformed, to end with the current stalemate.

Cameron L. Tracy’s article, “Sociotechnical risks posed by the geologic disposal of weapons plutonium,” discusses the risks of the US government’s plan to bury a large stockpile of excess weapons plutonium at the Waste Isolation Pilot Plant (WIPP), a geologic repository in southeastern New Mexico originally designed to store non-weapons nuclear wastes.

In their article, “Small and advanced nuclear reactors: Closing the fuel cycle?”, Claire Corkhill and her colleagues explain how developing new reactor designs, which often come with novel fuel, must go hand in hand with building disposal solutions for their radioactive waste to avoid future significant and unconstrained costs.

In an article published posthumously, Rodney C. Ewing and his long-time collaborator Bernd Grambow reflect on the reasons why the research community has not achieved a better understanding of the issue of safety in the geological disposal of radioactive waste, despite more than 50 years of effort. They offer some important advice to the next generation of repository experts.

I hope that Bulletin readers will find this special issue entertaining and insightful and that the articles in it do justice to Rod Ewing’s great contributions to science.