Overview of key themalhydraulic phenomena in severe accident unfolding: Current knowledge and further needs

Severe Accidents are closely and deeply linked with thermalhydraulics. This paper synthesizes such a relation during accident unfolding and provides an overview of the remaining gaps associated to thermalhydraulics that need to be addressed to properly reduce the uncertainties associated to SA and to optimize these events management. Some of those thermalhydraulic processes are common to other areas, but most of them are genuine of the SA domain, like corium and debris cooling, H2 distribution and combustion in containment and fuel-coolant interaction, just to mention a few. In addition to those processes of a bare thermalhydraulic nature, there are others governing SA consequences, like fission product transport and eventual release to the environment, that are heavily affected by thermalhydraulic boundary conditions and need to be investigated under the anticipated conditions. Anyway, there is a consensus that any investigation to be launched in the coming years should have a direct impact on reducing the uncertainties associated to their modelling and/or on optimizing their management.