Journal of Earth Sciences and Geotechnical Engineering

Microstructure controls physical properties of smectite clay

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• Abstract

   

  Environmental protection by isolation of radionuclides escaped from High-Level Radioactive Waste stored underground in crystalline rock can be achieved by surrounding the metal canisters by smectite clay, which provides hindrance of radionuclides to migrate into the surroundings, and ductile embedment of them for absorbing seismic and tectonic displacements in the host rock. The waste-isolating capacity of the expansive clay is explained by its high hydrophilic capacity and large specific surface area giving low porosity and limited interconnectivity of the voids, which both makes such clay low-permeable and gives it a very low through-diffusion rate of anionic species like iodine, and of some cationic radionuclides. The expandability of such clay means that it can swell and undergo self-healing in case of microstructural contraction caused by heating. The mechanisms involved in permeation and ion exchange are described based on conceptual microstructural models and their theoretical analogies. Stress/strain phenomena involved in saturation with fluids, desiccation, shearing under deviatoric conditions, and creep strain under stable conditions or at failure are described as well. Longevity matters, which have been richly treated in the literature, is given limited space. 

   

  Keywords: Smectite clay, montmorillonite, microscopy, clay microstructure.