UNDERSTANDING THE STRUCTURAL STABILITY OF RARE-EARTH CONTAINING PYROCHLORE-TYPE OXIDES FOR NUCLEAR WASTE SEQUESTRATION APPLICATIONS BY X-RAY SPECTROSCOPY

摘要

With the continued use of nuclear reactors to supplement civilian power needs, appropriate technologies need to be developed to deal with radioactive waste [1]. Current strategies for waste management include incorporating waste elements in silica glasses or placing spent nuclear fuel bundles in casks [1,2]. An alternative strategy is to heat a mixture of waste elements and appropriate binary metal oxides to high temperature to form a crystalline, ordered oxide structure that incorporates the waste elements, especially actinide elements, in distinct crystallographic positions [1,3]. The pyrochlore-type structure has received considerable attention as a potential nuclear wasteform owing to its compositional flexibility, enhanced resistance to structure damage caused by radioactive decay, and the high concentration of actinides that can be substituted into these materials [1,3]. Pyrochlore-type oxides can be represented by the following formula, A_2B_2O_7, where the A atoms are found in an 8-coordinate site while the B atoms are found in a 6-coordinate site [1].