Not all of the DOE-EM wastes can be managed by bulk waste processing technology, as highly volatile radionuclides including 129I and 135Cs cannot be effectively incorporated into a borosilicate glass waste form. Single phase crystalline ceramics or multiphase assemblages have been investigated as alternative waste forms to borosilicate glass for HLW, excess plutonium from dismantled nuclear weapons, and minor actinides separated during fuel reprocessing. The ceramics team targets fundamental understanding of radionuclide incorporation, confinement and transport behavior in bulk crystalline ceramics and across solid-solid and solid-liquid interfaces that can be closely linked with the ceramic waste form degradation and stability under near field conditions. The approach taken in this research is summarized in Figure 1.
Project C1: An Integrated Computation and Experimental Approach in Designing Waste Forms and Tailoring Performance
An integrated approach will be used for synergizing atomistic computations in probing radionuclide incorporation and confinement coupled with experimental demonstration, enabling a science-based design of new crystalline ceramic waste forms. This is based upon our success in designing and synthesizing apatite-structure types for iodine incorporation. For a more coherent and focused research, model systems will be selected, e.g., apatite, hollandite, and perovskite as promising waste forms for critical fission products (Cs, Sr, and I).
Project C2: Degradation Mechanisms of Crystalline Waste Forms.
In this project, we will focus on the understanding of the long-term degradation/corrosion of ceramic waste forms for critical radionuclides in understanding their release mechanisms with or without ionizing radiation. It is envisioned that the ionization radiation upon decay of radionuclides could have significant impact on the phase, microstructure and degradation of crystalline waste forms. Leaching experiments will be performed on model systems to achieve mechanistic understanding of the release behavior of specific radionuclides. We will particularly focus on the interfacial behaviors across the solid-liquid (surface alteration) and solid-solid (heterogeneous/homogeneous boundaries) interfaces to elucidate the dominant degradation mechanisms (e.g., through radionuclide diffusion or dissolution). Experimental and simulation techniques applied to ceramics will include those applied to the other materials classes. The mechanistic understanding of the simple ceramic model system will be synergized with the knowledge achieved by the glass team to understand the complex behavior of the multiphase glass-ceramic assemblages.