Modeling Solute in Clays at the Nanometric Scale Part I. Application to the Alcaline Series

N. Diaz1, F. Goutelard1, and P.Turq2
1CEA/DEN/DPC/SECR/L3MR, CEN Saclay, Gif-sur-Yvette, France
2LI2C, Université Pierre et Marie Curie, Paris, France

The argillite formation has been proposed as a potential host rock for deep radioactive waste disposal. These materials have very low permeability and diffusion is likely to be the predominant transfer mechanism for solute migration.

The negatively charged surface of the clays induces unexpected behaviour of the ions: while the anions diffuse slower than HTO, the transport of the cations is accelerated. To explain these two antagonistic phenomena, "effective diffusion porosity" for anions and "surface diffusion" for cations has usually been introduced.

The aim of the present study is to describe the main mechanism that takes place in the vicinity of the charged surface (nanometric scale) and enables to quantify the behaviour of the alcaline series (from Li to Cs), i.e increase the retention and effective diffusion coefficient from lithium to caesium.