In the framework of the 4th Periodic Safety Review (PSR) of the 1,300 MWe French Pressurized Water Reactor (PWR) series, in the streamline with previous PSR, Electricity of France (EDF) has developed a large span of Probabilistic Safety Analysis (PSAs) that cover Internal initiating Events (IE), but also internal hazards (fire, flooding, explosion) and external hazards (seismic, flooding, heat wave and high winds). To support its review of the EDF PSA, IRSN (as Technical Support Organization (TSO) of the French Nuclear Safety Authority (ASN)) has also developed in-house internal initiating events and limited scope hazard PSA. When performing hazard PSA, attention must be paid on the hazard characterization (magnitude/frequency), identification of the most important scenarios and assessment of the hazard impact on the plant and on the conditions to perform emergency human actions to mitigate the accident. Generally, the PSA assumptions are best estimate and may be different from the deterministic study conservative assumptions. As hazard PSAs cover many complex scenarios, it is a challenge to develop a complete set of representative supporting studies and to evaluate all hazard impacts on the plant and the human factors. In addition, the hazard characterization is challenging because representative data and operating experience are rare. Therefore, the interpretation of hazard PSA results, risk ranking, and safety insights must rely on an acute analysis of the PSA limits. This paper focuses on the recent lessons learned from the Level 1 internal flooding PSA developed or reviewed by IRSN.