In order to simulate some accidental scenarii which might affect a pressurized water reactor, a homogeneous two-phase water-vapor flow model taking into account non-condensable gas is considered. The liquid phase and the gaseous phase are assumed to be immiscible, but the gaseous phase is composed of two miscible components. Due to these hybrid hypotheses of miscibility, the configurations with at least one missing field are carefully examined. A semi-analytical equation of state is chosen for the liquid water, which is an extension of the Noble-Able stiffened gas equation of state. Its accuracy is assessed with respect to the reference equation of state IAPWS. The homogeneous model is first verified thanks to Riemann problems. Then, some simulations aiming at reproducing SUPERCANON experiment are presented. The amount of air dissolved in liquid water is shown to have a strong influence on numerical results, in particular on the sound speed. Some out of thermodynamical equilibrium simulations are also presented, using two time scales describing the return towards equilibrium.