Abstract: Prediction and comparison were conducted on the molten core-concrete interaction in the mixed and stratified pool configurations in a mega kilowatt pressure water reactor plant by using the code MEDICIS modeling methods in the aspects of pool concrete interface and heat transfer. The results show that the mean pool temperature is close to the molten core solidification temperature, the cavity ablation behaves isotropically, and the final temperature and pressure do not reach the designed values in the mixed pool configuration, while the mean pool temperature is far above the corium solidification temperature, the cavity ablation behaves anisotropically and the lateral ablation prevails, and the final temperature and pressure are very close to the designed values in the stratified pool configuration. Also in the both pool configurations, the concrete basemat is ablated quite slowly, the time of basemat melt-through in the containment may exceed a week for a 4 m thick basemat, the large masses of steam and incondensable CO, CO₂ and H₂ are produced in the containment, and there exists a risk of gas combustion and detonation which may be a threat to containment integrality.