Intergrowth Structure in U- and Hf-Bearing Pyrochlore and Zirconolite: Analytical Electron Microscopy Investigation

摘要

The concept of Synroc was originally proposed by Ringwood et al, and the first Synroc fabrication technology was developed by Dosch et al. During the last two decades, Synroc has been subjected to extensive studies. Synroc immobilizes radionuclides by incorporating them into appropriate phases and forming solid solutions. With large polyhedra (with coordination numbers ranging from 7 to 8) in the structures, Synroc is able to accommodate a wide range of radionuclides (e.g., actinides, Pu, U, Ba, Sr, Cs, Rb, Tc, etc.) as well as neutron absorbers (e.g., Gd and Hf). U- and Pu-loaded Synroc generally contains phases of pyrochlore and zirconolite. Various Syncroc formulations (e.g., Synroc-C, Synroc-D, Synroc-E, Synroc-F etc.) have been developed for specific high-level wastes. Homogeneity of sintered ceramics is an important factor to long-term chemical durability. This article describes chemistry and phase relation of Ce- and U-bearing pyrochlore and zirconolite. Ce~(3+), Ce~(4+), U~(4+), and U~(6+) in the studied crystalline phases may be used as chemical analogues for Pu~(3+), Pu~(4+), and Pu~(6+), respectively.