Potential Techniques for Krypton and Xenon Capture Processing and Storage in Solid Matrices

Radioactive noble gases (i.e., krypton and xenon) are produced in significant quantities during the fission of nuclear material and pose a challenging problem for containment due to their inert nature. Delayed, temporary storage in combination with environmental dilution/release into the atmosphere has been one of the primary historical methods for dealing with radioactive noble gases. However, shifts in geopolitical expectations for more responsible commercial nuclear practices are guiding the industry away from these practices in order to better ensure public safety and health. Now, innovative alternatives for potentially separating, capturing, and sequestering radiokrypton and radioxenon are being explored, although a suitable course of action for their long-term abatement has yet to be identified. This need is particularly important for radiokrypton, which requires longer-term storage/disposal to manage it safely.The primary objective of the proposed Phase I project is to investigate potential processing techniques for the capture and storage of radioactive krypton and xenon in solid materials. Two different approaches are being considered for this: 1) insertion and retention within hollow glass microspheres (HGM) and 2) ion implantation/sputtering into an appropriate metal substrate. Ideally, both options provide physically and chemically stable host phases for long-term disposal of krypton/xenon, which in turn allows for continuous removal and processing of these fission products. The project approach will be to integrate state-of-the-art technologies related to HGM and ion implantation and assess their viability for sequestering radioactive krypton and xenon.During Phase 1, the goal will be to explore the basic principles and designs of each methodology along with sourcing/characterizing necessary materials and performing the initial testing to determine viability. For HGM, two different routes for noble gas insertion will be investigated: (1) the use of prefabricated commercial materials in conjunction with processing techniques akin to hydrogen storage in HGM, and, (2) manufacture of HGM with simultaneous gas encapsulation. Historically, ion implantation/sputtering of radiokrypton into solid substrates has been explored but not adopted. There have, however, been significant advances in ion implantation technology and research on non-radioactive krypton and xenon ion implantation since this earlier work. Therefore, for ion implantation/sputtering for processing krypton and xenon, first-principles calculations, and computational modeling (i.e., Density Functional Theory (DFT)) will be performed to determine ideal metal substrates for noble gas sequestration. DFT modeling and results will dictate what materials will be suitable for follow-on experimentation. Ideally, samples will be generated using state-of-the-art ion implantation devices and techniques and tested to ascertain their performance. Comparison of new versus old systems will determine whether there is now merit for this technique.Providing an efficient pathway for handling, storing, and/or disposing of radioactive krypton and xenon potentially allows for commercial applications such as spent nuclear fuel (SNF) reprocessing, isotope production, and so forth to safely operate without having to discharge these hazardous materials into the environment. Likewise, it is not unreasonable to anticipate an increase in the overall efficiency and a corresponding reduction in operational costs and energy expenditure required to hold and store these waste streams.