In order to understand the jet breakup behavior of the molten core material into the coolant during a core disruptive accident (CDA) for a sodium-cooled fast reactor (SFR), we simulated the breakup using the lattice Boltzmann (LB) HCZ model The surface and fragmentation behavior was investigated in detail in the simulation results for examining the effect of ambient fluid around the jet As a result, we observed that the jet breaks up by fragmentation which occurs at side of the jet Thus, it was confirmed that the mechanism of the jet breakup behavior follows that of the Epstein's correlation when the dominant phenomenon for the jet break up is hydrodynamic fragmentation
