Radiological and hydraulic durability of alkali-borosilicate radioactive waste immobilization matrix prepared from industrial waste glass grit: Insights into the microstructure alterations

The viability of using alkali borosilicate glasses synthesized from industrial waste glass grit for strontium immobilization is preliminary evaluated by examining the immobilization system structure under normal short-term leaching and harsh conditions. The results designate that strontium is immobilized in alkali-borosilicate(ABS) media structure and led to increasing the structural disorder around the trigonal and tetrahedral units in the glass network. The presence of certain elements such as Na⁺, K⁺, Ca²⁺, Mg²⁺ are worked as glass modifiers that has donated to strontium immobilization in the glass structure. The chemical structure of both ABS and Sr-ABS samples is stable under the studied 80 KGy irradiation dose and there are breakage of some bonds due to the irradiation exposure. Leaching processes contributing to the cumulative leaching fraction of strontium, boron and sodium were quantified and the main governing leaching process for each studied element was identified. Multi-variate procedure was used to get insight into the effect of the leaching temperature, initial pH and leaching time on the final PH of the synthesized simulant waste matrix and the concentration and normalized leaching fraction of the strontium and sodium elements. The attained normalized release rates of strontium (N_r,i) are within the acceptable range of borosilicate glass at all the studied conditions. For simulated Sr-ABS matrix, strontium element is leached via dissolution and first order reaction, while boron and structural alkali Na are mainly leached via first order reaction.