In this study, the influence of the cooling water temperature on the thermal efficiency of a conceptual pressurized-water reactor nuclear-power plant is studied through an energy analysis based on the first law of thermodynamics to gain some new insights into the plant performance. The change in the cooling water temperature can be experienced due to the seasonal changes in climatic conditions at plant site. It can also come into the question of design processes for the plant site selection. In the analysis, it is considered that the condenser vacuum varies with the temperature of cooling water extracted from environment into the condenser. The main findings of the paper is that the impact of VC increase in temperature of the coolant extracted from environment is predicted to yield a decrease of similar to 0.45 and similar to 0.12% in the power output and the thermal efficiency of the pressurized-water reactor nuclear-power plant considered, respectively. Copyright (c) 2005 John Wiley & Sons, Ltd.