Improving safety has always been a fundamental objective in the nuclear industry and for the development of new reactors. Over the past 30 years, safety evaluations have evolved, with Probabilistic Risk Assessment (PRA) becoming a well-established procedure. Despite its widespread acceptance, PRA has limitations, including the possibility of overconservative results and the exclusion of the explicit interaction among time, repairs, physics and operator interventions. These limitations are particularly evident in specific cases that could benefit from a dynamic study, such as Generation IV Sodium-cooled Fast Reactors (SFR), which France has developed, constructed, and continues to design and study. New and more ambitious safety goals are key pillars in the development of Gen IV reactors.