Effects of Hydration on the Stability of Smectite Edge Surface Formation

Iodine and technetium-99 radionuclides are among those of concern for safe deep geological storage of used nuclear fuel (UNF) due to their high environmental mobility. Smectite clay materials have been considered as an additional protection feature against these isotopes due to their capabilities to capture ions (via adsorption) and to sufficiently swell in the region between vitrified UNF and surrounding rock. Even so, the adsorption behaviors of smectite edge surfaces are yet to be fully understood. Here, plane-wave density functional theory calculations are used to characterize the formation of (010), (100), (110) and (130) of isolated and hydrated edge surfaces of pyrophyllite and montmorillonite. Pyrophyllite is considered as a model for all smectites given its simple form and the consideration of isolated/hydrated surfaces provided the ability to quantifiably survey the impact of hydration on surfaces during termination processes while montmorillonite is a candidate clay material. Specifically, edge distortion will be discussed from a thermodynamic perspective throughout this presentation. This work was supported by funding received from the U.S. DOE Office of Nuclear Energy’s Nuclear Energy University Program under Project 20–19198.