Analysis of the radioactive source terms in severe accidents is crucial for nuclear power plants, as it significantly influences the calculation of the offsite consequence and frequency of large radioactive releases. The International Atomic Energy Agency has emphasized that a representative accident scenario should be selected and verified for each release category when applying an integrated accident analysis code, although the specific guidelines remain unclear. In this study, the integrated severe accident analysis code MAAP has been adopted to calculate source term categories for the advanced China pressurized water reactor.

The release fractions of source terms to the environment from different severe accident sequences are calculated, compared, and analyzed for five important release categories. The results show that initiating events will not cause significant effects on source term results within one release category, though the mitigation measures may cause a difference of at least one magnitude for a bypass release category and a containment filtration release category. Recommendations for selecting representative severe accident scenarios are provided, which has important practical values for performing safety analyses for nuclear power plants.