Evaluation on the entry conditions to severe accidents in domestic PWR NPPs using MELCOR2.2

Abstract

According to the Nuclear Safety Act amended in 2015, severe accidents are legally included in the scope of accident management. Due to the characteristics of severe accidents, both the NPP operator and the regulator should approach the severe accidents separately from Design Basis Accidents and multiple fault accidents. In the Nuclear Safety Act, the ‘Severe Accident’ is defined as “The accident in which the reactor core is seriously damaged beyond the scope of the design standards.” However, there is no quantitative criterion of the severe accident in domestic legislation or regulatory standards. In this study, the entry points to the severe accidents of domestic PWR NPPs were calculated using MELCOR2.2, and a method was proposed for conducting the comparative evaluation on the capability of delaying accident progression of each reactor. Furthermore, whether the quantitative entry condition to the severe accident described in SAMG is equivalent to the definition of the severe accident specified in the Nuclear Safety Act was evaluated through the comparison with DBA standards.