In the present study, the Yonggwang 1, 2 plant cavity mock-up is used to investigate the behavior of the core melt material in the reactor cavity. Water is used as simulant of the core melt material and air is used for gas blowdown. The relations between the fraction of the melt ejected from the cavity and the conditions of the pressure vessel for gas blowdown phase are investigated. As a result of this study, the melt ejection mechanism of the melt in the Yonggwang 1, 2 plant cavity is identified as ``particle levitation``. The dispersal criterion of ``particle levitation`` in present study is compared with the Zion Probabalistic Safety Study (ZPSS) analysis. Fraction of the melt ejection is dependent on the initial conditions of the pressure vessel at the time of the pressure vessel failure. It is affected by such factors as the reactor break size, the blow-down pressure, and the gas velocity in the cavity. However, the fraction of the melt ejected from the cavity is not dependent on the degree of core damage in the pressure vessel.