Abstract: In order to predict the diffusion process of bentonite colloids in the fractures of surrounding rocks in the deep geological repository of high-level radioactive waste in Beishan, Gansu, a diffusion model that integrates the self-weight of bentonite colloid particles and hydration force is proposed. The effects of sodium ion concentration, hydration force, self-weight of colloid particles, and volume fraction of montmorillonite on the diffusion process and diffusion coefficient of bentonite colloids were investigated. The results show that both the diffusion rate and diffusion distance of bentonite colloids decrease with the increase of sodium ion concentration. The greater the self-weight of colloidal particles, the more significant their impact on diffusion. As the diffusion proceeds, the influence of hydration force on diffusion gradually decreases, while the influence of van der Waals force and diffusion double-layer force gradually increases, and in general, the diffusion coefficient of bentonite colloids decreases first and then increases. When the volume fraction of montmorillonite is small (φ <0.45), the diffusion coefficient generally increases with the increase of sodium ion concentration; when the volume fraction of montmorillonite is large (φ >0.45), the influence of sodium ion concentration on the diffusion coefficient is relatively small.

Key words: bentonite colloids, colloid diffusion model, diffusion coefficient, particle self-weight, hydration force