Several TOUGH2 Modules Developed for Site Characterization Studies of Yucca Mountain

A comprehensive site characterization study has been conducted for the unsaturated zone (UZ) of Yucca Mountain to investigate its suitability as a potential high-level nuclear waste repository. Numerical modeling of moisture, gas, chemicals and heat flow, and their influence on the repository performance has been proven to be essential in understanding unsaturated-zone fluid movement, and the effects of hydrogeologic, geochemical and thermal conditions on various aspects of the overall waste disposal system. In these studies, the TOUGH2 code has been used extensively as a main modeling tool because of its flexibility and robustness in handling multiphase, multi-component fluid and heat flow and chemical transport in porous/fractured rocks. As part of the UZ modeling efforts at LBNL, several new modules of the TOUGH2 code have been developed to meet different needs of the site characterization studies. In this paper they will summarize some of these new TOUGH2 modules and their specific features in application to the Yucca Mountain project. These new TOUGH2 modules include (1) the effective continuum model (ECM) for treating fracture/matrix flow; (2) single-phase gas flow (EOS1G) in a water-air two phase flow system; and (3) a 3-D radionuclide transport module (T2R3D) for 3-D radionuclide or tracer transport in porous/fractured media under two-phase flow and non-isothermal conditions