Analysis of Process for Core Melt and Debris Pool Formation in IVR Evaluation for CPR1000

In-Vessel Retention（IVR） is an important and crucial method for preventing and mitigating the consequences of severe accidents.In this paper,a lot of severe accident sequences are selected under investigation according to the related laws and regulations,and then calculated by an integral severe accident analysis computer code to get the details of debris pool in lower head and their effects on the heat focusing effect.The results show that: there is a marked heat focusing effect on the height of metal layer in debris pool and the vessel can get its integrality under external reactor vessel cooling.