An Assessment Methodology of Thee-Layers Melt Configuration during IVR for AP1000

In-Vessel Retention Analysis Model（IVRAM）is formulated to assess the thermal response of the Two-Layers melt configuration and Thee-Layers melt configuration during IVR for AP1000 with anticipative depressurization and reactor cavity flooding in severe accident. The results of the calculations for the melt configuration show that the presence of the heavy metallic layer at the bottom of the lower head decreases the thickness of the top light metallic layer and consequently increases the risk of focusing effect, the focusing effect of the light metallic layer increases with the increase of the thick of heavy metallic layer.