Development of rapid atmospheric source term estimation system for AP1000 nuclear power plant

The development of rapid atmospheric source term estimation system (RASTES) for AP1000 nuclear power plant (NPP) is described. The system is designed to give rapid estimation of the amount of fission products released to the atmosphere, and to provide necessary input for fission products atmospheric dispersion simulation and public dose calculation, during a nuclear accident. The estimation method in RASTES mainly refers to NUREG-1228. However, some adjustments are made based on an investigation of studies in nuclear emergency response and design features of AP1000 NPP during development of RASTES. These adjustments enable the system to be more flexible and realistic in atmospheric source term estimation, and more applicable to AP1000 NPP. These adjustments include modifications and validations of aerosol removal factors in reactor containment in both natural process and spray process, as well as addition of aerosol removal factors in passive containment cooling process. Besides, three reactor core damage assessment methods are integrated into atmospheric source term estimation. In addition, containment radiation levels for specified fuel damage which are used in core damage assessment are recalculated. The calculation function of RASTES is confirmed through comparison with RASCAL. Atmospheric source terms in different fission product removal processes are also calculated and compared. The result shows that passive containment cooling is able to further reduce aerosol release by about 50% compared with natural process. Development of RASTES will enhance the capability of nuclear emergency response of AP1000 NPP.