Corrosion behavior of LaPO4 glass solidification in bentonite, humic acid, and groundwater for spent fuel geological repositories

The application of nuclear energy plays a crucial role in the advancement of global energy systems; however, sustainable development is inherently linked to the effective management of high-level waste produced by nuclear power generation. The disposal of nuclear waste involves encapsulation to create a stable waste form that is buried deep within geological repositories, ensuring ecological separation from human activities. Consequently, the corrosion resistance of the encapsulated material is vital for preventing leakage. This study examines the embedding properties of iron phosphate glass–coated LaPO₄ ceramics and evaluates the impact of corrosion factors such as bentonite, humic acid, and groundwater. The corrosion mechanisms were analyzed under acidic, neutral, and alkaline conditions. It was determined that the glass solidification can be embedded at a maximum concentration of 30 wt.%, with bulk density increasing alongside the embedding ratio. Notably, bentonite and glass solidification exhibit greater reactivity in acidic environments compared to neutral and alkaline conditions. Additionally, the glass solidification materials undergo hydration due to groundwater influence, leading to the corrosion of the glass surface and the formation of new crystalline phases, including H₄P₂O₆·2H₂O, Fe₅(PO₄)₃(OH)₅·2H₂O, and rhombohedral calcium zeolite (Ca₄Al₈Si₈O₃₂·8H₂O). The corrosion rate analysis indicates that lower pH levels correlate with increased corrosion rates in acidic conditions, particularly in the absence of humic acid. These findings provide a robust foundation for the future development of underground laboratories and the advancement of geological disposal technologies for high-level waste.