Partition behavior of strontium in SYNROC

SYNROC formulations aimed at immobilizing civilian high-level wastes comprise 3 major phases; hollandite, perovskite and zirconolite (SYNROC-C). It has been shown experimentally that Sr is strongly partitioned into perovskite, with lesser amounts entering zirconolite, and very little (typically <<0.2%) entering hollandite. Zirconolite + hollandite: the 2-phase SYNROC formulation is of interest because even without perovskite, it has the capacity to successfully immobilize civilian wastes. Elements such as rare earths and strontium which are largely partitioned into perovskite in SYNROC-C formulations would instead be accommodated by zirconolite. The experiments imply that this could be achieved without any difficulty. Calcined civilian wastes typically contain 2 to 3% SrO, thus for a 2-phase SYNROC comprising 40 wt.% zirconolite and 60% hollandite, with a waste-loading of 10 wt.%, the SrO content of zirconolite would be about 0.7 wt.%. This is well below the saturation limit of zirconolite. The possibility of developing a modified SYNROC assemblage in which CaTiO3 perovskite was replaced by SrTiO3 was investigated. The specific experiment tested the compatibility between SrTiO3 and CaZrTiO7 at 5 kbar, 13000C. These phases were found to be incompatible, and the results show that Strontian SYNROC is not a viable concept