Influence of Different Hypotheses Used in Numerical Models for Concrete at Elevated Temperatures on the Predicted Behaviour of NPP Core Catchers Under Severe Accident Conditions

Numerical analyses of the behaviour of a NPP core-catcher under core melt down accident have been carried out. The capability of different numerical models to predict the behaviour of this structure has been scrutinised. A thermo-elastic-plastic model for concrete at elevated temperatures including cracking and thermomechanical interaction strains has been developed for this analysis. Comparisons with the results obtained with a simplified model are presented. Particular attention has been paid to the effects of thermomechanical interaction on the predicted behaviour of the foundation raft. Neglecting this phenomenon leads to a strong overestimation of thermal induced cracking in the structure. (authors)