An Overview of the Crystal Chemistry, Durability, and Radiation Damage Effects of Natural Pyrochlore

Abstract

ABSTRACTNumerous studies of pyrochlore group minerals have been completed over the previous 15 years, providing researchers in the field of nuclear waste disposal with a large body of data relevant to the behavior of these minerals in natural systems. The information obtained from studies of natural pyrochlore is applicable to the formulation of diverse waste form compositions and provides data for the assessment of the long-term behavior. Although resistant to dissolution, pyrochlore is subject to chemical alteration by ion exchange with hydrothermal fluids and low temperature ground water; however, Th and U are generally immobile and are retained in the structure. X-ray diffraction, TEM, EXAFS-XANES, and other techniques have been employed in studies of radiation damage. These studies reveal the classic sequence of damage microstructures with increasing dose and provide details about the structure of the amorphous state. Furthermore, the radiation damage studies are now complemented by data relating to the thermal histories of some of the host rocks.