Comparative Study of SBO and LOOP Accidents Severity from Core Catcher Design Point of View; Application to IR360 Nuclear Power Plant

The most severe postulated events (called bounding case) should be considered for effective evaluation of system design in nuclear power plants. In this article the most severe case for evaluation of core catcher design is discussed. Among the most important boundaries for mitigation of severe accident effects, core catcher is the last one. Severe accidents are divided into two categories: Low Pressure (LP) and High Pressure (HP). From the core catcher point of view, HP accidents are more severe because the corium is evacuated to the core catcher at a higher pressure, and the possibility of failure is increased. Among the HP severe accidents, the most severe cases belong to the Station Black Out (SBO) and Loss of Offsite Power (LOOP). After Fukushima Daiichi accident, most of the published researches illustrate that SBO is the bounding case in nuclear power plant severe accidents. In this study, MELCOR code is used to compare the severity of an SBO and a LOOP for the core catcher design. The first step in this analysis is development and verification of a steady state MELCOR model of the IR-360 plant. Then, in the severe phase, the SBO and LOOP accidents are simulated using MELCOR for the IR-360 plant. Finally, the results are compared with each other. According to results it is concluded that the LOOP is more severe than the SBO from the core catcher point of view.