An analysis of radiological releases during a station black out accident for the APR1400

An analysis on the behavior of fission products during a station blackout (SBO) accident for the APR1400 nuclear power plant is performed using MELCOR version 2.1. The analysis is focused on investigating the characteristics of radiological releases from the damaged fuel in the reactor core and molten corium in the reactor cavity, transport of the radioactive materials in the reactor coolant system and containment, and release of the radioactive materials to the environment. It is shown that the release characteristics of radionuclides from the fuel, distributions of radionuclides in the reactor coolant system and containment strongly depend on the species of radionuclides. In cases of volatile radionuclides such as iodine and cesium, more than 95% of initial inventory is released before the reactor vessel failure. The amount of radionuclides released to the environment after a failure of the containment was significantly reduced due to the deposition of radionuclides in the form of aerosols on the surfaces of heat structures and a pool of water in the containment. A sensitivity study on the presence of water in in-containment refueling water storage tank (IRWST) shows that the water in the IRWST significantly reduced the amount of radionuclides released to the environment.