This study aims to bridge standardized leaching test data with the underlying radionuclide transport mechanisms in cemented radioactive waste forms. Analysis of experimental data obtained in accordance with the Chinese standard GB 14569.1-2011 reveals that radionuclide release occurs in two distinct stages: an initial fast-release phase, governed by surface reactions, followed by a slow-release phase, controlled by diffusion through the pore structure. In intact cemented systems, matrix dissolution is negligible and can be excluded from long-term predictive models. Fast leaching percentage and fast leaching reaction constant can be derived for the early 14 days leaching data. The slow apparent diffusion coefficient can be derived from the data collected after 35 days, and these derived parameters agree well with dual porosity model. However, radionuclide-specific behavior must be accounted for 60Co and 137Cs. For 60Co since a decrease in leachate pH (e. g., due to carbonation) can enhance the dissolution of Co(OH), thereby increasing its release rate, and for 137Cs, competitive ion effects from Na+/K+ in the pore solution significantly accelerate desorption, indicating that a desorption-controlled diffusion model is more appropriate for long-term performance assessment than a simple Fickian diffusion model. These findings strengthen the mechanistic interpretation of regulatory leaching tests and support more robust safety evaluations of cement-based waste forms in China.
Meilan et al. (Thu,) studied this question.