Ternary Phase Diagrams that Relate to the Plutonium Immobilization Ceramic

摘要

The plutonium immobilization ceramic consists primarily of a pyrochlore titanate phase of the approximate composition Ca0.97Hf0.17Pu0.22U0.39Gd0.24 Ti2O7. In this study, a series of ternary phase diagrams was constructed to evaluate the relationship of various titanate phases (e.g., brannerite, zirconolite-2M, zirconolite-4M, and perovskite) to pyrochlore titanates, usually in the presence of excess TiO2 (rutile), and at temperatures in the vicinity of 1350 degrees C. To facilitate the studies, U, Th, and Ce were used as surrogates for Pu in a number of the phase diagrams in addition to the use of Pu itself. The effects of impurity oxides, Al2O3 and MgO, were also studied on pyrochlore (Gd2Ti2O7) and zirconolite (CaHfTi2O7) mixtures. Either electron microprobe (at Lawrence Livermore National Laboratory) or quantitative SEM-EDS (at Australian Nuclear Science and Technology Organization) were used to evaluate the compositions of the phases.