A computational procedure suitable for modeling both vertical and horizontal steam generators is presented. The procedure consists of a one-dimensional model for the whole steam generator and a CFD model for the secondary side. The three-dimensional two-phase CFD simulation of the secondary side utilizes the porous medium approximation and the mixture k-e turbulence model. One-way coupling between the models is used, in which the surface temperatures of the heat transfer tubes are considered as a boundary condition for the CFD simulation. A stationary state and two pressure transients, a pressure rise and a pressure reduction, for the PWR PACTEL steam generator are calculated and the internal circulation on the secondary side is analyzed. PWR PACTEL is a test facility, located at Lappeenranta University of technology, in Finland, which was constructed for research activities associated with the European Pressurized Reactor (EPR).