KRAK: A computer program for two-phase two-component porous flow and fracture

The KRAK code models the mass, momentum, and energy flow of steam, liquid water, and a noncondensable gas in a porous medium. It can model the initiation and propagation of hydrofracture in this medium by any or all of the fluid components using finite difference techniques. The interaction of the flow and the cracking is self-consistently performed. Flow in the crack is treated by a full-momentum equation, which allows rapid fracturing. The code was used in studies of the underground containment of radioactive gases produced by nuclear explosions and of siting underground nuclear power reactors. The code could also be applied to a wide variety of geophysical situations such as geothermal energy extraction, geysers, convection in a fractured medium, and explosive well stimulation. The physical model includes heat transfer between the porous medium and the flowing fluid, an equation of state of fluid condensation and evaporation, a model for the viscosity of each fluid component and the composite viscosity, and a permeability model that treats interfaces of greatly differing permeabilities. Cracking is controlled by a simple fracture mechanics model.