Synthetic Minerals with the Pyrochlore and Garnet Structures for Immobilization of Actinide-Containing Wastes

Complex oxides of the pyrochlore (space groups Fd3m, ([8])A(2)([6])B(2)O(7)) and garnet (Ia3d, ([8])A(3)([6])B(2)([4])T(3)O(12)) structures (A = Ca2+, Ln(3+/4+), An(3+/4+); B = (Ti, Sn, Hf, and Zr)(4+) in pyrochlore, and Al3+, Ga3+, and Fe3+ in garnet alone; T = (Al3+, Ga3+, and Fe3+) 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 Cm-244 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 incor-porating long-lived decay products of Tc-99 into the crystalline matrices was analyzed.