Chemical durability and leaching mechanisms of simulated radioactive glass waste forms for the early stage

Reliable performance assessment of the radioactive glass waste forms under disposal scenarios requires a mechanistic and kinetic understanding of radionuclide leaching, which, however, remains inadequately understood. Herein, the mechanisms and kinetics associated with early-stage leaching of major constituents and surrogate radionuclides (i.e., stable isotopes) from two typical types of simulated radioactive glasses (i.e., borosilicate and aluminosilicate glasses) with or without simulated high-level waste (SHLW) incorporated was systematically investigated by integrating pH- and temperature-dependent leaching tests, glass structure characterizations, and geochemical/kinetic modeling. Results showed that aluminosilicate glasses exhibited superior early-stage chemical durability compared with borosilicate glasses, owing to their higher Si and Al contents that enhanced resistance to proton attack and hydrolysis. Incorporation of alkali-rich SHLW disrupted the polymerized glass network, weakening its structural integrity and decreasing its chemical durability for the early stage. Ion exchange mechanism dominated the leaching behavior of most constituents under acidic conditions. The release of Cs, Sr, and Re (as an indicator for Tc) followed glass dissolution kinetics and was well captured by the kinetic model, whereas the leaching of Se and Co was influenced by secondary phases (e.g., hydroxides, silicates, and mineral adsorption) as identified by geochemical speciation modeling. These findings provide mechanistic and kinetic foundations for developing predictive models and conducting performance assessments of radioactive glasses in field conditions.