Microstructure and performance studies of (Mo,Ru,Pd,Zr) tetra-doped gadolinium zirconate pyrochlore

Abstract

Proper disposal of nuclear waste with multi-nuclides and multi-valence is still challenge. A series of (Mo, Ru, Pd, Zr) tetra-doped Gd₂Zr₂O₇ ceramics were studied to understand the microstructure and performance evolution of nuclear waste forms that immobilised simulated waste after trialkyl phosphine oxides (TRPO) process. The structure of as-obtained samples were tested by X-ray diffraction, Raman, scanning electron microscope, electron back-scattered diffraction, and energy-dispersive X-ray spectroscopy, while the mechanical and chemical performance were characterised by Vickers hardness and aqueous leaching method. The results indicate that the mechanical behaviour are closely linked with the phase structure, and the highest Vickers hardness is obtained at the phase turning point. The leaching results show that the normalised leaching rate (LR) of the doped elements decrease in the order of Mo, Ru, Pd, Zr. After reaching equilibrium, their LR are as low as 4.12 × 10⁻⁴ g·m⁻²·d⁻¹, 1.50 × 10⁻⁵ g·m⁻²·d⁻¹, 1.30 × 10⁻⁵ g·m⁻²·d⁻¹, and 2.09 × 10⁻⁷ g·m⁻²·d⁻¹, respectively.