[en] This report first explains the mission which aimed at determining requirements related to the increase of the safety level of 900 MW French nuclear reactors and which will be used as a basis in case of extension of the exploitation duration, and briefly presents some characteristics and features of these PWRs. It presents information related to their technology: operation principle, indications related to electric power supply and to safeguard arrangements and equipment in case of accident. Then, it gives an overview of levels of safety requirements to be adopted for a project of extension of the lifetime of a nuclear reactor: application of the generally scientifically and technically acknowledged level to existing reactors in France, rules and directives (national, international, European) to be used as a basis for requirement profiles, determination of requirement profiles (for the protection against external aggressions, in terms of independence and lack of connection between safety equipment or between units of a same site). It discusses the implementation of current safety requirements in French 900 MW reactors according the periodic safety re-examination as it is applied in France, and proposes a synthesis of necessary requirements to improve the safety of these reactors within the framework of an exploitation on the long term