A: Radioactive samples are suspended in a gas stream and heated with lasers.
B: Plutonium oxide samples start as matte gray but turned shiny black after heating.
C: The inset shows a sample after heating in pure oxygen.
[Credit: Image by Argonne National Laboratory.]
Researchers at Argonne successfully measured and analyzed the structure of molten plutonium oxide (PuO2) at temperatures reaching 3,000 Kelvin. The experiment involved levitating tiny, 2-millimeter samples of PuO2 on a gas stream and heating them with a powerful carbon dioxide laser. Using the brilliant X-rays produced by Argonne’s Advanced Photon Source, the team captured detailed snapshots of the molten PuO2’s atomic structure.
The researchers, joined by Stephen Wilke and Rick Weber of Materials Development, among others, published the results in Nature Materials.
In the abstract of the paper, the scientists describe the behavior and structure of PuO2–x above 1,800 K as “largely unexplored,” adding that “these conditions must be considered for reactor design and planning for the mitigation of severe accidents.” Their work revealed that “Molten PuO1.76 contains some degree of covalent Pu–O bonding,” and importantly, that “The liquid is isomorphous with molten CeO1.75, demonstrating the latter as a non-radioactive, non-toxic, structural surrogate.” The research, the scientists conclude, “provide essential constraints for modelling pertinent to reactor safety design.”
A collaborative effort
The Argonne research was fundamentally collaborative, as Mark Williamson, division director of Argonne’s Chemical and Fuel Cycle Technologies (CFCT) division, noted in a press release: “This has been a fantastic collaboration of experts, and it’s an excellent example of how we work together to continually improve nuclear energy systems.”
Chris Benmore, senior physicist at Argonne National Laboratory, emphasizes the facility’s singular position in this field: “Argonne is probably the only place in the world capable of performing this very difficult type of experiment.”
Rekindling interest in nuclear science
The field of nuclear science has undergone something of a quite renaissance in recent years, thanks to growing interest in clean energy and alternative fuel sources, including nuclear fusion. Outside of Argonne National Laboratory’s research on molten plutonium oxide at extreme temperatures, the U.S. Department of Energy (DOE) achieved a historic breakthrough in 2022 by reaching fusion ignition at Lawrence Livermore National Laboratory (LLNL). This milestone marked the first time that more energy was produced from fusion than was used to drive the reaction. The company General Atomics, whose research played a role in the fusion breakthrough, won the R&D Team of the Year as part of the R&D Professional Awards in 2024 thanks to the work of its Metrology Research and Development Team on the 4Pi Integrated Metrology System that was used in the fusion breakthrough and has since helped make fusion more reliable through further integration of robotics.
Argonne is also working on next-generation reactor designs. In the private sector, companies like TerraPower have also explored that subject. As of 2024, TerraPower has announced progress with its first Natrium advanced nuclear reactor, which it expects to be operational by 2030. Founded by Bill Gates, TerraPower submitted a construction permit application for the reactor to the Nuclear Regulatory Commission (NRC) in March 2024, according to Reuters.
