Partial elimination of the perovskite phase in Synroc

Abstract

Perovskite is the least durable of the crystalline titanate phases comprising Synroc, a ceramic designed for the immobilisation of high-level waste from nuclear fuel reprocessing. Because 4 perovskite and the other titanate phases (zirconolite, Ba hollandite and reduced titania) are mutually compatible, adjustments to the Synroc mineralogy can be made in principle by adjusting the overall chemical composition. However, the alkoxide route to Synroc is necessary to eliminate perovskite, since perovskite forms metastably and persistently when less reactive precursors to Synroc are employed. The presence of the nuclear waste ions modifies the crystalline phases present and some chemical accounting is necessary to achieve the desired phases constitution. The properties of low-perovskite preparations are compared in detail with those of the current Synroc composition, particularly in regard to leaching and phase constitution.