Improvement of evaluation of the contact pressure upon the penetration of a reactor lower head during a severe accident: Part 1. Conceptualization considering elastic deformation

When damaged core materials are relocated to the reactor lower head with penetrations during a severe accident, the loss integrity of the reactor pressure vessel caused by ejection of a penetration tube will occur earlier than the global failure of the reactor lower head. The overall aim of this study is to review and improve the previous contact pressure evaluation models. In this part of the study, it was shown that the previous model in the elastic region only considers the deformation of a penetration tube itself by assuming one hollow cylinder with a limited stress-strain condition. Therefore, the new expression of the contact pressure at the interface was derived by stress analysis with assumption of additional concentric outer cylinder for a reactor lower head. The new contact pressure model was validated using finite element analysis.