Advanced study of transport analysis in bentonite

Kawamura, Katsuyuki*

Solute and radionuclide transport analysis in buffer material of bentonite day is essential in safety assessment of a geological disposal facility for high-level radioactive waste (HLW). It is keenly required to understand the true physical and chemical process of the transport phenomena and to improve reliability of the safety assessment, since any conventional methods based on experimental models involve difficulty to estimate the level of robustness. For this purpose we start with the molecular dynamics (MD) simulation method to know molecular-based fundamental properties such as an ionic state and diffusion characteristics of hydrated smectite clay minerals, and we intend to extend the microscale properties to the macroscale behaviors by applying the multiscale homogenization method. In the current year study we introduced a detailed study of MD simulation of hydrated clay minerals, and observed microstructures of bentonite by using a confocal laser scanning microscope (LSM). In the MD simulation first a new interatomic potential model was introduced for water molecules. Then the behaviors of hydrated Na-beidellite and its substitution products by Cs and Ca were calculated. Hydrated muscovite and pyrophyllite were also treated. A three-phase system of clay minerals with edges, water and gas is finally was considered to check the behaviors of cations and water molecules near the edges. A microscopic image is important to specify micro/macro behavior of bentonite. We used the LSM (Ar-laser, wave length 488nm) to characterize the microscopic geometry of bentonite. We could observe a 3-D configuration under atmospheric condition to get images of Kunigel V1 (a well-known bentonite in Japan) and Kunipia F (a refined bentonite including 99% of montmorillonite). By using the advantage of LSM we observed swelling properties of bentnite particles under several salt concentration conditions.