Estimation of the mechanical consequences of a steam explosion with a local approach - Thermalhydraulic and mechanical linked computations

In the frame of the PWR severe accident studies, hypothetical energetic steam explosions are considered if large amounts of molten corium fall into the reactor lower plenum. The mechanical consequences of an in-vessel steam explosion on a PWR lower plenum vessel are correlated to the explosion itself and to the whole premixing phase preceding the explosion. Therefore, taking into account precisely and locally the initial conditions of the explosion improves greatly the precision of the evaluations of the mechanical consequences of the explosion on the reactor pressure vessel.As the french thermalhydraulic code MC3D is able to provide reliable assessments of the fragmentation of a corium jet issued from the core melting and as the french general fast dynamics code CASTEM-PLEXUS can perform computations of the steam explosion and of the vessel response, it was undertaken to initialize the steam explosion calculations of CASTEM-PLEXUS from the local data of the premixing phase computed by MC3D.This paper presents the method used to link both codes. The main characteristics of the codes and of the linkage method are analyzed. An application concerning the computation of an in-vessel steam explosion resulting from a large central core degradation is also described.