Dissolution Behavior and Kinetics of Insulating Glass Wool under Highly Alkaline Conditions

This study aimed to evaluate the long-term stability of glass wool used as insulation material in domestic nuclear power plants and to quantify its degradation mechanisms and dissolution kinetics under highly alkaline conditions (pH ≥ 12) expected in cementitious environments associated with vault-type disposal systems for low-level radioactive waste. Experiments were conducted at 20°C and 80°C using cement-saturated groundwater (CGW) as the primary solution, while comparative tests were performed in NaOH and Ca(OH)₂ solutions at equivalent pH levels. ICP-OES, SEM-EDS, and XRD analyses revealed that dissolved Ca²⁺ significantly suppressed glass dissolution. The presence of abundant Ca²⁺ ions promoted densification of the surface alteration layer, retarding degradation, whereas depletion of Ca²⁺ resulted in a rapid increase in the dissolution rate. Although calcium silicate hydrate (CSH) precipitates are generally known to inhibit glass corrosion, the CSH phases formed in this study exhibited limited protective capability due to their low Ca/Si ratios and high porosity. Based on the dissolution rate constant at 20°C, the complete dissolution of glass wool was estimated to require approximately 213 years; however, under conditions of limited Ca²⁺ availability, the dissolution rate could increase by up to 70-fold, approaching that observed in NaOH solution.