Multiphase multicomponent nonisothermal reactive transport in partially saturated porous media

A numerical model MULTIFLO is developed for describing reactive transport in a multiphase-multicomponent, nonisothermal, partially saturated porous medium. The model includes chemical reactions between aqueous, gaseous and solid phases. Reactions involving minerals are considered to be irreversible and described through appropriate kinetic rate laws. Homogeneous reactions within the aqueous phase and heterogeneous reactions between aqueous and gaseous phases are assumed to be reversible, their reaction rates controlled by transport and local equilibrium mass action relations. Flow of aqueous and gaseous phases is described by Darcy's law in a partially saturated porous medium. Solute transport includes contributions from advection, diffusion and dispersion. Enhanced binary diffusion of water vapor for transport in a two-phase system is taken into account. A sequential solution algorithm is used to couple transport of water, air and heat to solute and minor gas components, and solids. Changes in porosity and permeability caused by chemical reactions are coupled to the flow field. Several options are available for solving numerically the solute and gaseous transport equations including fully implicit, explicit and operator splitting methods. Mineral mass transfer equations are solved using an explicit finite difference scheme. The coupled flow and transport model is applied to the proposed high-level nuclear waste storage facility located in unsaturated rock at Yucca Mountain, Nevada. A repository-scale model is used to calculate the redistribution of moisture, heat, and various chemical constituents caused by the thermal perturbation produced by the waste. (author)