[en] Clad ballooning may substantially decrease the flow of fluids through the affected core region and may expose the inner cladding surface to oxidation in the vicinity of rupture sites. The cladding ballooning model was not included in MELCOR 1.8.4. and consideration of incorporating the cladding ballooning model is scheduled as a post-1.8.4 release activity. The purpose of this paper is to analyze the effect of the clad ballooning model by the modified MELCOR 1.8.4 with this model. The typical accident sequence of a large LOCA scenario is selected. The clad ballooning model accelerates the accident progression compared to that without the ballooning model. The amount of hydrogen does not change much and it may be caused by ignoring the effect of flow area change. Future study is planning to analyze the flow redistribution