The penetration of intermittent low-carbon energies in the French electric mix challenges the need of enhancing the manageability of the French nuclear fleet. Most of the French nuclear reactors have been devised to do load-follow operations in order to ensure the supply and demand balance anytime. However, it has been shown that the less the share of electricity production from nuclear energy (which would be mainly compensated by the development of wind and solar energy), the more load-follow transients will be planned to manage summertime peak of electric over-production or conversely winter season peak of underproduction. A coupling between the secondary loop and the cooling circuit of a pressurized water reactor has been implemented in addition to a simulator oriented French 1300 MW reactor model. We present here our modeling of the steam turbines, the moisture separator, the water reheater and the condenser for a typical P’4 French nuclear reactor provided with an open-loop cooling circuit. As we study off-design load conditions, we simulate a load transient based on real electricity production profile done in the past few years. We compare the temperature of the water withdrawn from the cold source downstream of the plant measured on site and the one we calculate from our model.