PSA Level-2 Study: Estimation of Source Term for Postulated Accidental Release from Indian PHWRs

Abstract

Source term is generally known as the amount of the radionuclides (fission products along with activation and actinides) that get released from a nuclear power plant in an accident. Since the release of radionuclides depends on accident scenario, various plant damage states which include design basis accident and severe accident with and without core meltdown have been considered in a systematic way as a part of PSA level-2 study with containment event tree during release categorization. Detailed study was done to estimate the source term for Indian 220 MWe PHWR with current understanding of radionuclide release from core and behavior of it in primary heat transport (PHT) system and containment. The major factors affecting potential radionuclide releases into environment as a result of nuclear power plant accidents are described. Engineering safety features play an important role to control and reduce the radionuclide release to environment. It is shown that during accident, release to environment is reduced if containment integrity is maintained. Well-established accident management guidelines exist for every Indian nuclear power plant to mitigate the accident progression. Using containment filtered venting system, containment integrity can be maintained if containment is over-pressurized, and effect of it to reduce the radionuclide release to environment is discussed. Based on the release of radionuclides to environment, final release category has been defined, which helps to know the severity of accident, and accordingly, emergency preparedness can be done. The estimated source term will be used for PSA level-3 study.