Abstract: Based on the integration program of MELCOR for severe accident analysis, the computational model of a typical marine reactor was established. The creep failure of pressurizer surge tube in the accident of blackout was verified, and the behavior of the source term before and after the break of surge tube was analyzed. The results show that atmospheric environment and crew would suffer the radioactive harm. The smaller the surge tube break, the slower the accident process. However, the external radiation of the crew is slightly increased and the internal radiation is unchanged. The research results can provide a basis on further dose analysis of the source term and the emergency action inside and outside the ship.