Natural Pyrochlores: Analogues For Actinide Host Phases in Radioactive Waste Forms

Significant amounts of the pyrochlore structure type, and derivative structures like zirconolite, have been reported to occur in crystalline, polyphase, nuclear waste forms [1,2,3,4]. Pyrochlore has abundant and chemically diverse natural analogues. Many of these contain U and Th and have been transformed to the electron-diffraction amorphous, “metamict” state by alpha-recoil nuclei. A variety of geochemical alteration processes may occur before, during, and after reaching the final saturation level for alpha-recoil damage (∼1026 alpha-events/m3 ). The purpose of this paper is to examine these alteration effects in radiation-damaged natural pyrochlores.