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Journal of Porous Media

Impact factor: 1.035

ISSN Print: 1091-028X
ISSN Online: 1934-0508

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Journal of Porous Media

DOI: 10.1615/JPorMedia.v12.i8.10
pages 725-748

Modeling of Coupled Heat Transfer and Reactive Transport Processes in Porous Media: Application to Seepage Studies at Yucca Mountain, Nevada

Sumit Mukhopadhyay
Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
Eric L. Sonnenthal
Lawrence Berkeley National Laboratory, USA
Nicolas Spycher
Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

ABSTRACT

When hot, radioactive waste is placed in subsurface tunnels, complex changes are expected to occur in the surrounding rocks. Water in the pore space of the medium may undergo vaporization and boiling. Subsequently, vapor may migrate out of the rock pore space, moving away through the permeable fracture network. This migration can be propelled by buoyancy, by the increased vapor pressure resulting from boiling, and through convection. In cooler regions, the vapor may condense, where it can drain through the fracture network. Thereafter, imbibition of water may lead to rewetting of the rock matrix. These thermal and hydrological processes may also bring about chemical changes in the rocks. Amorphous silica can precipitate from boiling and evaporation, and calcite from heating and CO2 volatilization. The precipitation of amorphous silica and calcite can lead to long-term permeability reduction. Evaporative concentration also results in the precipitation of gypsum (or anhydrite), halite, fluorite, and other salts. These evaporative minerals eventually redissolve after boiling ceases; however, their precipitation may lead to a temporary decrease in permeability. Reduction of permeability is also associated with changes in fracture capillary characteristics. In short, the coupled thermal-hydrological-chemical (THC) processes may dynamically alter the hydrological properties of the rock. A model based on the TOUGHREACT reactive transport software is presented here to investigate the impact of these THC processes on flow near an emplacement tunnel at Yucca Mountain, Nevada. We show how transient changes in hydrological properties caused by THC processes may lead to local flow channeling and seepage.