In order to analyze the FCI, MCCI, and DCH, information on the vessel ablation diameter is essentially needed. In this study, we developed the ablation model using heat balance equations for molten corium flow, crust layer, and molten wall film, respectively. Also we proposed the calculation method in order to determine the heat transfer coefficient applicable for molten corium discharge out of the reactor vessel using CFD calculation. It is based on the external turbulent correlation multiplied by the correction factor determined by CFD analysis considering real geometry and real materials. In order to reflect the effect of the crust formation on the molten wall film layer, the critical molten wall thickness concept was introduced and obtained by CFD. The ablation model was well validated with a mean error of 9.34% which is much smaller than those from the model of MELCOR. Also we investigated the impacts of the current model on the penetration-depth during FCI and containment pressure during DCH in real nuclear power plants.