Phase Development and Sintering Studies on an Immobilized Pu Ceramic Form

The Department of Energy (DOE) plans to immobilize at least some of the excess weapons useable plutonium in a ceramic form for final geologic disposal. The proposed immobilization form is a titanate based ceramic consisting primarily of a pyrochlore phase with lesser amounts of brannerite, rutile, perovskite, zirconolite and/or glassy phases. The ceramic formulation is cold-pressed and then densified via a reactive sintering process. The sintering process results in approximately 20 percent shrinkage from the green state. The final phase assemblage appears to be the result of several reactions occurring during the reactive sintering process. In this study, thermal analysis techniques were coupled with x-ray diffraction analysis (XRD) in an attempt to identify reaction temperatures and mechanisms occurring during the heating process. Several low temperature reactions involving calcium in various chemical states were identified. The in-growth of perovskite was also pinpointed as well as the development of the primary phase - pyrochlore. The formation of pyrochlore in the ceramic was found to coincide with the onset of densification