Crystal chemistry of natural zirconolite: implications for high-level waste disposal in Synroc

Zirconolite, ideally CaZrTi2O7, is a relatively rare mineral crystallizing at different geological conditions and in a wide range of generally SiO2-poor rock types. Synthetic zirconolite is one of two major actinide (ACT) host phases in SYNROC, a very promising option for the disposal of high-level nuclear waste (HLW). The available samples of naturally occurring zirconolite cover an extensive range in ACT content, age and host rock type, and thus offer an ideal opportunity to study the relationships between alpha-decay doses, radiation damage, and geochemical alteration processes [1]. In this paper, we present results obtained from a statistical study of nearly 300 chemical analyses of natural zirconolite [2].