Overview of key thermal–hydraulic phenomena in severe accident unfolding: Current knowledge and further needs

•Thermal–hydraulics plays an essential role in severe accident unfolding and most accident management actions.•Deep understanding of thermal–hydraulics is mandatory to reduce severe accident uncertainties and get an optimum management.•A list of thermal–hydraulic issues worth to be investigated from the severe accident perspective has been set.•Two key aspects of further investigation should be: representative experimental conditions and scaling.•Innovation into the research should come from new technologies (SMRs; ATFs) and new modeling approaches (BEPU; AI).