Geochemical modelling of hydrogen gas migration in an unsaturated bentonite buffer

This paper presents an investigation of the transport and fate of hydrogen gas through compacted bentonite buffer. Various geochemical reactions that may occur in the multiphase and multicomponent system of the unsaturated bentonite buffer are considered. A reactive gas transport model, developed within an established coupled thermal, hydraulic, chemical and mechanical (THCM) framework, is presented. The reactive transport module of the model considers the transport of multicomponent chemicals both in liquid and gas phases, together with an advanced geochemical reaction model. The results of a series of numerical simulations of the reactive transport of hydrogen in unsaturated bentonite are presented in which hydrogen gas, because of the corrosion of a steel canister, has been injected at a realistic rate into a partially saturated bentonite buffer. Gas pressure development and the fate of the hydrogen gas with respect to the geochemical reactions are studied. The results show the high buffering capacity of unsaturated bentonite, when considering a steel canister, over a period of 10 000 years. The presence of accessory minerals is shown to have an important role in mitigating excess hydrogen ions, thus increasing the dissolution capacity of the system to gas. The development of various forms of aqueous complexations between the inorganic components and the hydrogen ions were also found to be important in buffering the excess hydrogen that evolved. Based on the results obtained, it is postulated that the presence of various chemical components in the clay buffer may influence the transport and fate of the hydrogen gas.Geoscience & EngineeringCivil Engineering and Geoscience