Combustion reaction synthesis of Y2-xGdxTi2O7 pyrochlores and its aqueous durability as nuclear waste mateiral

Abstract:

Pyrochlore-based ceramic is recognized as promising nuclear waste matrice. In this study, pyrochlore-based Y_2-xGd_xTi₂O₇/Cu composite waste forms were rapidly prepared within 5 minutes by combustion reaction plus quick pressing (CR/QP) synthesis route, where CuO was utilized as the oxidant and Ti as the reductant. As the surrogate of trivalent actinide nuclides, Gd was introduced to substitute the Y site with nominal formulation of Y_2-xGd_xTi₂O₇. The results demonstrate that Gd can totally replace the Y site and Gd₂Ti₂O₇ pyrochlore can be readily synthesized. There is no impurity phase generated in the products, and phase separation is not detected in the pyrochlore matrix. The selected Gd_1.0 waste form exhibits promising aqueous durability as the 42 days normalized leaching rates of Cu, Y and Gd elements are evaluated as low as 2.4×10^_-2, 1.1×10^_-5 and 5.3×10^_-6 g.m^_-2.d^_-1.

Key words:Combustion;reaction synthesis, Nuclear;waste, Pyrochlore, Chemical;durability.