Inductive cold crucible melting of actinide-bearing murataite-based ceramics

Abstract

Murataite-based ceramics doped with U or Th were produced by inductive cold crucible melting (ICCM) at operating frequencies of 1.76 and 5.28 MHz and examined using X-ray diffraction and scanning and transmission electron microscopy. Three distinct murataite polytypes were identified in the U-bearing ceramics: a five- (5C), eight- (8C), and three-fold (3C) fluorite unit cell crystals that respectively make up what is designated as the core, intermediate and rim zones. In contrast, the Th-bearing ceramic contained only the five-fold (5C) fluorite unit cell polytype. The core zone of the murataite in the U-bearing specimens is characterized by UO 2 concentrations as high as 12.1 wt%, which successively diminishes in concentration through the intermediate zone to the rim, the latter of which contains 5.2 wt% UO 2. On the other hand, Th distribution within the murataite crystals is uniform. The difference in phase composition and actinide partitioning in the ceramics is influenced by synthesis conditions. Larger cold crucible size ensures lower crystallization rate yielding zoned crystals with maximum actinide concentration in the core of the murataite crystals that minimizes exposure of the actinide elements to potential leach solutions.