Self-propagating high-temperature synthesis,phase composition and aqueous durability of Nd–Al bearing zirconolite-rich composites as nuclear waste form

Abstract

In this study, the zirconolite-rich composite was rapidly synthesised from self-propagating high-temperature synthesis plus quick pressing using MoO₃ as the oxidant and Ti as the reductant. As a surrogate of trivalent actinides, Nd was introduced to substitute the Ca site of zirconolite and Al was employed as the charge compensator to replace the Ti site (nominally Ca_1−xNd _x ZrTi_2−xAl _x O₇). The phase composition and Nd occupancy were analysed after Nd₂O₃ addition. Nd-bearing zirconolite was produced as the major ceramic phase. Nd mostly substitutes the Ca sites of zirconolite, which results in waste loading higher than 8.6 wt-% Nd. The aqueous durability of Nd–Al codoped sample (with 15 at.-% Nd substitutes the Ca site of zirconolite) was evaluated at 90°C as well. The 42 days normalised leaching rates of Mo, Ca and Nd were measured to be 3.70, 1.90 × 10⁻² and 3.46 × 10⁻⁴ g m⁻² d⁻¹.