Severe accident management technology for SMART

System-integrated modular advanced reactor (SMART) - a Korean integral reactor - has been developed. It comprises a core, reactor coolant pumps, steam generators, and a pressurizer within a single reactor pressure vessel. For safety enhancement, SMART can adopt the inherent and passive safety, simplified safety system, or advanced man-machine interface. For economic enhancement, SMART can apply system simplification and component modularization. For operation enhancement, SMART considers a simplified operation strategy and convenient maintenance. The nominal thermal power of SMART is 365 MW_th. For safety enhancement, SMART utilizes a severe accident management technology comprising (1) vessel depressurization, (2) reactor cavity flooding, and (3) a hydrogen control system. In (1), an automatic depressurization system (ADS) is utilized to prevent direct containment heating (DCH) in case of a reactor vessel failure. In (2), a cavity flooding system (CFS) is utilized to prevent a reactor vessel failure. The cavity flooding system comprises an in-containment refueling water storage tank (IRWST) for in-vessel corium retention through external reactor vessel cooling (IVR-ERVC). The hydrogen control system (3) is utilized to remove hazards from hydrogen combustion considering the amount of hydrogen to be generated by 100% fuel cladding oxidation. Equipment to mitigate the effect of a severe accident in SMART has been installed, and it complies with safety goals and criteria for containment performance. Severe accident mitigation systems are normally functioned in a severe accident environment, which is not necessary for the safety class. Equipment to cool the outer wall of and the melted core material inside the reactor vessel is installed. Equipment to prevent a hydrogen explosion and the occurrence of a direct containment heating phenomenon, which can cause an early failure of the containment, has been installed. It comprises passive autocatalytic recombiners (PARs), which serve to maintain the total hydrogen concentration below 10%, including hydrogen generated from the 100% cladding oxidation reaction. Under the IVR-ERVC condition, the water from the IRWST is flooded into the reactor cavity passively by gravity. A reactor vessel insulation used to reduce the heat loss during normal operation has been installed between the outer reactor vessel and the reactor cavity wall. A water inlet, steam outlet, and water circulation outlet have been installed in the reactor vessel insulation for IVR-ERVC. The required systems for IVR-ERVC are safety depressurization using an ADS, a CFS with IRWST, a reactor cavity design, and a reactor vessel insulation design for water contact to the outer reactor vessel wall and for use with generated steam venting. (author)