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, ACu ₃ FeTi ₃ O ₁₂ (A = Nd, Ce, Pu), using sol-gel methods under oxidizing and reducing atmospheres. The targeted materials contained varying levels of Ce ³⁺ and Nd ³⁺ on the A site, yielding potential compositions of Nd _1-x Ce _x Cu ₃ FeTi ₃ O ₁₂ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.8). However, interrogation of these materials shows that the maximum Ce ³⁺ loading is achieved near x 0.2. A single composition with plutonium was targeted, Nd _0.9 Pu _0.1 Cu ₃ FeTi ₃ O ₁₂ , 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 Pu ³⁺ substitution onto the A sites in the Nd _0.9 Pu _0.1 Cu ₃ FeTi ₃ O ₁₂ , 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 TiO ₂ .