A three-dimensional (3-D) two-fluid model for a turbulent stratified flow with and without condensation is presented, in view of investigating pressurized thermal shock (PTS) scenarios when a stratified two-phase flow takes place in the cold legs of a pressurized water reactor. A modified turbulent K-ε model is proposed with turbulence production induced by interfacial friction. A model of interfacial friction based on an interfacial sublayer concept and three interfacial heat transfer models—namely, a model based on the small eddies–controlled surface renewal concept, a model based on the asymptotic behavior of the eddy viscosity, and a model based on the interfacial sublayer concept—are implemented into a preliminary version of the NEPTUNE code based on the 3-D module of the CATHARE code. As a first step, the models are evaluated by comparison of calculated profiles of velocity, turbulent kinetic energy, and turbulent shear stress with data in a turbulent air-water stratified flow in a rectangular channel and with data for a water jet impacting the free surface of a water pool. Then, a turbulent steam-water stratified flow with condensation is calculated, and some first conclusions are drawn on the interfacial heat transfer modeling and on the applicability of the model to PTS investigations.