Conversion of nuclear waste to molten glass: Formation of porous amorphous alumina in a high-Al melter feed

The transition of Al phases in a simulated high-Al high-level nuclear waste melter feed heated at 5 K min⁻¹ to 700 °C was investigated with transmission electron microscopy, ²⁷Al nuclear magnetic resonance spectroscopy, the Brunauer-Emmett-Teller method, and X-ray diffraction. At temperatures between 300 and 500 °C, porous amorphous alumina formed from the dehydration of gibbsite, resulting in increased specific surface area of the feed (∼8 m² g⁻¹). The high-surface-area amorphous alumina formed in this manner could potentially stop salt migration in the cold cap during nuclear waste vitrification. - Highlights: • Porous amorphous alumina formed in a simulated high-Al HLW melter feed during heating. • The feed had a high specific surface area at 300 °C ≤ T ≤ 500 °C. • Porous amorphous alumina induced increased specific surface area.