Preparation and characterization of powellite ceramics Ca1-xLix/2Cex/2MoO4 (0 ≤ x ≤ 1) for Mo-rich HLW condition
Powellite ceramic represent one candidate to immobilize minor actinides and Mo from reprocessed UMo nuclear fuel. In this work, the Ca 1-x Li x/2 Ce x/2 MoO 4 (0 ≤ x ≤ 1) series is prepared via a solid-state reaction using Ce 3+ as trivalent minor actinide (Am 3+ ) surrogate, with structure/microstructure characterized by XRD , XPS, HRTEM , and SEM as well. The Ca 1-x Li x/2 Ce x/2 MoO 4 (0 ≤ x ≤ 1) compositions crystallize in tetragonal and are isostructural with scheelite. Rietveld refinements show that Ce 3+ 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 Ca 1-x Li x/2 Ce x/2 MoO 4 (0 ≤ x ≤ 1) ceramics, 7-days NL Ce and NL Mo 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 NL Ce and NL Mo are predominantly controlled by the distortion of MoO 4 tetrahedra and disordered arrangements of Ce 3+ 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.
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