Support to the validation of a 900MW pressurized water reactor simulator. The simulators use is increasing in the science field. Indeed the development of calculation code and simulation tools is making the modeling of a system easier. At EDF the group “Process simulation” is developing simulation tools for the actual operating plants but also for the next generation of nuclear reactors. One main simulator used in this group is SiRENE meaning Renovated Simulator for Studies which is a full scope simulator of a 900MW or 1300MW pressurized water reactor. The main objective of my project is the support to the validation of the 900MW version of SiRENE.