Abstract: The simulation of formation of debris bed from degraded fuel rods is performed in an accident sequence of SBLOCA with station blackout for Qinshan nuclear power plant using ICARE2 V3mod1.3. The calculation results show that the core starts to degrade from 4 832 s and the related formation of debris bed is simulated until (10 000 s) when 30 000 kg solid debris and 10 000 kg liquid debris are produced. The (analysis) shows that the whole progress of core degradation is relatively fast due to poor core cooling conditions.