Abstract
Scanning Electron microscopic (SEM) observations for micropore structure in compacted bentonite and through-diffusion experiments for non-sorptive tritiated water (HTO) were conducted in order to evaluate the effect of clay mineral content and the compacted direction of bentonite on the orientation of clay particles and nuclide diffusive pathway in compacted bentonite used as a buffer material in the geological disposal of high-level radioactive waste. The SEM observations and through-diffusion experiments were conducted for axial and perpendicular directions to the compacted direction of bentonite as a function of bentonite's dry density. Two types of Na-bentonites, Kunigel-V1® and Kunipia-F® with different smectite contents, which are major constituent clay mineral, were used in both experiments. No orientation of clay particles was found for Kunigel-V1® with 50wt% smectite content, while layers of clay particles orientated in the perpendicular direction to compacted direction were observed for Kunipia-F® with approximately 100wt% smectite content. This trend is in good agreement with that for the effective diffusivities of HTO obtained from diffusion experiments. This indicates that smectite content in bentonite affects the orientation of clay particles and diffusive pathway.
