[en] Besides the long term safety research whose main purpose is to develop and improve safety analysis tools, the lessons learned from the TMI accident showed that the emphasis should be given on small break analysis, with multiple failures or not, to have a thorough understanding of nuclear power and decay heat removal processes in its many modes in order to develop good plant procedures. The impact of these studies on the design and on the emergency procedures, resulting from the licensing process, are described and the needs for the future are identified