Synthetic and natural minerals as matrices for actinide waste immobilization

Full text: The key issue for solution of the problem of actinide-containing radioactive wastes disposal is reliable immobilization of the long-lived actinides in highly durable containment matrices (waste forms). Reality of this way for safe actinide waste streams management is confirmed with results on study of their natural analogs-radioactive minerals with high contents of Th, U, and REEs. In spite of these minerals were subjected to irradiation due to actinides decay and interaction with underground waters for a very long period of time (millions of years) they have demonstrated a strong retardation of these elements in their structure. Main requirements applied at appropriate actinide waste forms selection include: high isomorphic capacity in respect of radioactive waste components, resistance to radiation damage and corrosion by hot water solution, and possibility for economically efficient industrial-scale fabrication. In this presentation we have discussed structural-chemical properties and the behavior under irradiation and underground water attack for various minerals of pyrochlore, zirconolite, monazite, and britholite groups. These minerals are considered to be the most perspective host phases for long term actinide immobilization. Besides, peculiarities of some synthetic compounds doped with actinides are also characterized. Main attention is paid to the phases with garnet and murataite structure that have no radioactive minerals - analogs in the nature. The data were obtained with different analytical techniques: XRD, SEM/EDS, TEM (HRTEM), XPS. Results of the research show that safe immobilization of actinides may be provided with containment matrices only. (author)