Application of recursively coupled FE-models to a PWR In-Vessel-Retention analysis

The improbable scenario of a severe accident with core meltdown and formation of a melt pool in the lower plenum of a Light Water Reactor (LWR) Pressure Vessel (RPV) can result in the failure of the RPV and the discharging of the melt to the containment. One accident management strategy could be to stabilize the in-vessel debris or melt pool configuration in the RPV as one major barrier against uncontrolled release of heat and radionuclides into the containment of the plant.
Based on the successful simulation and analysis work of the FOREVER-experiments the models have been developed further to simulate the prototypical scenario of an In-Vessel-Retention in a large German PWR (KONVOI). As shown in an earlier publication a recursively coupled simulation between the thermal and the mechanical model has to be performed to consider the mutual influence of the heat fluxes respectively the temperatures and the mechanical vessel behaviour.
After the validation of the recursively coupled thermal and mechanical FE-models against the scaled FOREVER-tests the models were improved to simulate a prototypic scenario under certain assumptions. The calculations show that an In-Vessel-Retention might be possible for large PWRs like KONVOI, if the RPV is flooded externally. The remaining vessel wall thickness seems to be sufficient to prevail even higher pressure loads. But in any case a support of the lower head would increase the margin to failure and therefore ensure the integrity of the last barrier within the containment of the plant.