Self-Propagating Synthesis and Characterization Studies of Gd-Bearing Hf-Zirconolite Ceramic Waste Forms

Synroc is recognized as the second-generation waste matrice for nuclear waste disposal. Zirconolite is one of the most durable Synroc minerals. In this study, Gd and Hf were selected as the surrogates of trivalent and tetravalent actinide nuclides. Gd-bearing Hf-zirconolite (Ca_1-xHf_1-xGd_2xTi₂O₇) ceramic waste forms were rapidly synthesized from a self-propagating technique using CuO as the oxidant. The results indicate that Gd can concurrently replace the Ca and Hf sites. However, Gd₂O₃ could not completely be incorporated into the lattice structure of zirconolite when the x value is higher than 0.8. The aqueous durability of selected Gd-Hf codoped sample (Hf-Gd-0.6) was tested, where the 42 days normalized leaching rates (LR) of Ca, Cu, Gd and Hf are measured to be 1.57, 0.13, 4.72 × 10^-7 and 1.59 × 10^-8 g·m^-2·d^-1.