Dissolution Mechanisms of CaTiO3 - Solution Analysis, Surface Analysis and Electron Microscope Studies Implications for Synroc

Tailored Perovskite Waste Forms for Plutonium Trapping

Perovskite ceramics have been extensively studied as host matrixes for radionuclide entrapment for nuclear waste disposal. As an expansion of these investigations, cerium, neodymium, and plutonium were incorporated into a perovskite phase, ACu₃FeTi₃O₁₂ (A = Nd, Ce, Pu), using sol-gel methods under oxidizing and reducing atmospheres. The targeted materials contained varying levels of Ce³⁺ and Nd³⁺ on the A site, yielding potential compositions of Nd_{1- x}Ce _xCu₃FeTi₃O₁₂ ( x = 0, 0.1, 0.2, 0.3, 0.4, 0.8). However, interrogation of these materials shows that the maximum Ce³⁺ loading is achieved near x ≈ 0.2. A single composition with plutonium was targeted, Nd_0.9Pu_0.1Cu₃FeTi₃O₁₂, in order to properly model more realistic loading levels for a repository-destined material. These compounds were characterized using powder X-ray diffraction with Rietveld refinements of the structures and by a variety of spectroscopic techniques. The data suggest that, in order to achieve Pu³⁺ substitution onto the A sites in the Nd_0.9Pu_0.1Cu₃FeTi₃O₁₂, a reducing atmosphere must be employed. Otherwise, the redox activity of plutonium results in substitution onto multiple sites in the material as well as the formation of secondary phases such as TiO₂.