Preparation and characterization of powellite ceramics Ca1-xLix/2Cex/2MoO4 (0 ≤ x ≤ 1) for Mo-rich HLW condition

Abstract

Powellite ceramic represent one candidate to immobilize minor actinides and Mo from reprocessed UMo nuclear fuel. In this work, the Ca1-xLix/2Cex/2MoO4 (0 ≤ x ≤ 1) series is prepared via a solid-state reaction using Ce3+ as trivalent minor actinide (Am3+) surrogate, with structure/microstructure characterized by XRD, XPS, HRTEM, and SEM as well. The Ca1-xLix/2Cex/2MoO4 (0 ≤ x ≤ 1) compositions crystallize in tetragonal and are isostructural with scheelite. Rietveld refinements show that Ce3+ and Li+ simultaneously enter into the eight-fold coordinated Ca site of powellite crystal. The chemical durability of powellite phases is evaluated by the ASTM C1285-14 product consistency test method B. The leaching behaviours of Ce and Mo are accordance with the interfacial dissolution-reprecipitation mechanism. For all the Ca1-xLix/2Cex/2MoO4 (0 ≤ x ≤ 1) ceramics, 7-days NLCe and NLMo are found to be in the order of 10−3-10−5 g·m−2 and 10−2-10−4 g·m−2 respectively, which exhibit the great retention of Ce and Mo. Interestingly, the values of 7-days NLCe and NLMo are predominantly controlled by the distortion of MoO4 tetrahedra and disordered arrangements of Ce3+ and Li+. Thus, our initial understanding on the structure and chemical durability relation will provide insight to design new waste forms for the Mo-rich HLW condition.