Design Principles of Optimizing Cementitious Glasses for the Disposal of Radioactive Waste

ABSTRACT We designed, synthesized, and characterized 26 cementitious calcium‐magnesium aluminosilicate (CMAS) glasses using the chemical and mineralogical properties of ordinary Portland cement (OPC), ground, granulated blast furnace slag (BFS), and class F fly ash as bounding conditions. The compositions ranged from 31.3–43.8 mol% SiO 2 , 2.8–14.3 mol% Al 2 O 3 , 32.1–52.1 mol% CaO, and 0.0–23.1 mol% MgO. The designed compositional space closely resembled that of reported BFS compositions. Our purpose for this design was to create glasses that would react with aqueous simulated low‐level radioactive waste (LLW) solutions upon contact and form solid phases over time. The glasses’ structure was determined via Raman spectroscopy and was correlated with exothermic heat release measured by isothermal calorimetry. We observed a moderate to strong correlation between an increasing degree of depolymerization and increasing heat flow ( R 2 = 0.66–0.78). After the completion of the isothermal calorimetry experiments, we examined the resulting solidified materials and observed no free‐standing liquid—an important property for low‐level waste disposition. Powder X‐ray diffraction patterns collected on five representative solids, approximately 3 months after completion of the calorimetry experiments, contained reflections consistent with calcium‐silicate hydrate and layered double hydroxide phases, supporting—though not conclusively demonstrating—that cementitious reactions occurred between the glasses and the simulated LLW.