Synthetic minerals with the pyrochlore and garnet structures for immobilization of actinide-containing wastes

Complex oxides of the pyrochlore (space groups Fd 3 m , [8] A 2 [6] B 2 O 7 ) and garnet ( Ia 3 d , [8] A 3 [6] B 2 [4] T 3 O 12 ) structures (“A” = Ca 2+ , Ln 3+/4+ , An 3+/4+ ; “B” = (Ti, Sn, Hf, and Zr) 4+ in pyrochlore, and Al 3+ , Ga 3+ , and Fe 3+ in garnet alone; “T” = (Al 3+ , Ga 3+ , and Fe 3+ ) are promising matrices for actinide-bearing wastes. In order to identify optimal compositions of these phases, their isomorphic capacity with respect to REE, actinides, and other components of wastes was examined. The long-term behavior of the matrix at a repository was predicted based on data obtained on the behavior of pyrochlores and garnets under ion irradiation and 244 Cm decay and on the determined leaching rates of REE from the matrices because of their interaction with aqueous solutions, including that after amorphization. In order to propose efficient synthesis techniques, samples prepared with the use of various methods were studied. The possibility of incorporating long-lived decay products of 99 Tc into the crystalline matrices was analyzed.