Calcite Dissolution and CO2 Generation under Deep Geological Repository Conditions

Abstract

Spent nuclear fuels and other long-lived radioactive wastes are proposed to be disposed in the deep geological repository (DGR) in rock layers 500 m below the ground surface. The repository will use a multi-barrier system including a repository host rock and engineered barrier system to minimize potential radionuclide transport to the environment. A major concern of DGR operation is the increasing gas pressure produced in the repository and hence radionuclide transport through dissolved gases and separate gas phases. The over-pressurization of the repository due to gas generation can result in safety issues including expansion of pores in the barrier, fracture formation and eventual release of radionuclides to the environment. Calcite, a ubiquitous mineral in nature and a polymorph of calcium carbonate, can be present in radioactive waste and in the geological rock layers surrounding the area of DGR. Dissolution of calcite can produce a significant amount of carbon dioxide especially under acidic and irradiated conditions. There is a lack of experimental research on natural calcite dissolution and the effects of gas generation and transport in DGRs. This paper will present recent results of calcite dissolution and carbon dioxide generation rates under various geochemistry conditions around proposed DGR sites. These experimental data will be used to support the numerical modeling of gas transport in DGRs.