Geochemical model for 14C transport in unsaturated rock

This paper reports that 14C in a geologic nuclear waste repository could be released to the gaseous phase and escape to the accessible environment through partially saturated fractured rock. Interaction with the carbon system in the ground can lead to retardation of 14C. A mechanistic interpretation of 14C retardation and release is provided by a model that couples nonisothermal gas flow and water saturation, carbon distribution based on local equilibria among gas, liquid and solid phases, and C and 14C transport. Repository heating is predicted to volatilize carbon from the liquid phase and to promote calcite precipitation. 14C transport is retarded principally by incorporation in the aqueous phase. A portion of early released 14C can be fixed in precipitated calcite for thousands of years