The thermodynamic efficiency of typical conventional and nuclear power plants is insufficient. A large amount of the generated heat is removed to the environment and regarded as a waste. A solution which is commonly used to increase the efficiency and profitability of the existing and planned power plants refers to cogeneration of heat and power. To prepare sophisticated thermodynamic and economic analyses, a precise static model of the steam/water cycle of the considered power plant is essential. The paper presents a methodology to build a static model of the steam/water cycle of the Nuclear Power Plant with Pressurized Water Reactor. The discussed model was prepared using phenomenological and network approach, complemented by a precise reference model as data source. The prepared model is believed to be very useful in thermal and economic efficiency analysis.