Structure and chemical durability studies of powellite ceramics Ca1−xLix/2Gdx/2MoO4 (0 ≤ x ≤ 1) for radioactive waste storage.

Powellite ceramic represents a waste form matrix material to immobilize minor actinides and Mo from reprocessed UMo nuclear fuel. In this paper, the Ca1−xLix/2Gdx/2MoO4 (0 ≤ x ≤ 1) series is prepared by solid-state reaction using Gd3+ as trivalent minor actinide (Cm3+) surrogate, and the structure/microstructure is characterized by XRD, HRTEM, Raman spectroscopy and SEM. Rietveld refinements show that the couple (Gd3+ and Li+) enters into the eightfold coordinated Ca site of the powellite structure. With the increase in the contents of Gd and Li, Raman bands broaden due to the distortion of MoO4 tetrahedra and disordered arrangements of Gd3+ and Li+. The chemical durability analyzed by the PCT-B indicates that the leaching behaviors of Gd and Mo are related to the interfacial dissolution–reprecipitation mechanism. For the Ca0.5Li0.25Gd0.25MoO4 ceramic, 7-day NLGd and NLMo are shown in the order of ~ 10−4 and ~ 10−4 g m−2, respectively. Thus, our initial results of the structure and chemical durability will provide insights to design new single- or multiphase waste forms for the Mo-rich HLW conditioning. [ABSTRACT FROM AUTHOR]