Non-isothermal vapor transport in a single unsaturated rock fracture

Abstract

Heat released by the radioactive decay of high level nuclear waste in an underground repository causes a long-terra thermal disturbance in the hydrologic flow field. Moisture transport through unsaturated fractured rock in the presence of this imposed temperature field will presumably be dominated by the vapor phase. Non-isothermal vapor transfer is investigated for the simplified case of a single unsaturated horizontal rock fracture. Analytic solutions for heat transfer, rock matrix water flow, and gravity drainage are solved numerically. The resulting temperature and moisture regime is then indirectly coupled to a Galerkin finite element solution for Fickian water vapor diffusion through the diffusion coefficient for water vapor in air, the vapor density gradient and the source/sink term. The results demonstrate the importance of temperature and vapor diffusion with regard to evaporation/condensation, micro-fracture drainage and the production of dry and wet zones in a fracture.