Clayrock formations are under consideration to serve as host formation and geological barriers for radioactive waste repositories due to their favorable properties (low permeability, low diffusion coefficient, high retention capacity for radionuclides...). The currently on-going European CATCLAY project (EURATOM FP7) (www.catclay.org) is focused on understanding the fundamental processes governing the diffusion-driven transport of cationic species in natural clayrocks. The project combines modeling with experimental studies of migration of three cations (Sr+2, Zn+2 and Eu+3) in a monophasic compacted clay (illite) system, considered to be an analogy for the clay matrix constituting clay-rocks, and three different clayrocks (Callovo-Oxfordian argilites (FR), Opalinus Clay (CH), Boom Clay (BE)). Part of the experimental studies are focused on the small scale structural (µm to nm) properties of the different materials in order to determine how the spatial distribution of mineral and pores at small scales can influence diffusion driven transport of cations. The present study focuses on compacted illite properties in hopes of extending this study to the natural clayrocks. Clay-rocks are more complex and include other mineral phases such carbonates or quartz. Our approach is mainly based on imaging the small scale structural organization of compacted illite material and analyzing the resulting images in order to extract information on pore space geometry/morphology and mineral spatial distribution, in order to use them as input data for transport modelling.
