Crystallization of Simulated High-Level Nuclear Waste Glasses Under Heat Treatment and Its Impacts on Glass Durability

Vitrification is currently the primary choice worldwide for high-level nuclear waste immobilization. This study investigated the crystallization behaviors of glasses containing 24%(mass fraction) and 30% simulated high-level nuclear waste, respectively, under different temperatures. According to X-ray diffraction, Raman spectroscopy and scanning electronic microscopy results, dendritic powellite(CaMoO₄) phase and string-like Zr-cerianite (ZrxCe_1-xO₂) are the main crystalline phases when the glasses are heat treated at 800 ℃, while a great amount of hollow hexagonal oxyapatite(Ca₂Ln₈(SiO₄)₆O₂) phases are observed in addition when the glasses are heated at 950 ℃. The chemical durability test shows that the heat treatment decreases the total normalized leaching mass loss of glass by about 1/3, with main contributions from B, Na, Mo and Ca. The normalized leaching mass loss of the glasses after heat treatment at 950 ℃ is smaller than that after heat treatment at 800 ℃. It indicates that the heat treatment of glass for crystallization improves glass durability.