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 Ca 1−x Li x/2 Gd x/2 MoO 4 (0 ≤ x ≤ 1) series is prepared by solid-state reaction using Gd 3+ as trivalent minor actinide (Cm 3+ ) surrogate, and the structure/microstructure is characterized by XRD, HRTEM, Raman spectroscopy and SEM. Rietveld refinements show that the couple (Gd 3+ 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 MoO 4 tetrahedra and disordered arrangements of Gd 3+ 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 Ca 0.5 Li 0.25 Gd 0.25 MoO 4 ceramic, 7-day NL Gd and NL Mo 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.