[NURETH-20] Evaluation on mitigation performance of flooding safety system under hypothetical loss of coolant accident in Korean i-SMR with MELCOR code

Abstract

In response to the growing interest in Small Modular Reactors (SMRs) globally, many countries are actively pursuing the development of high-power SMRs, based on their inherent advantages including enhanced safety, grid flexibility, and potential for hydrogen production. Among these endeavors, an i-SMR with an electrical power output of 170 MWe has been under development since 2021 by Korea Hydro & Nuclear Power Co., Ltd. in Republic of Korea. The i-SMR has established ambitious top-tier requirements, such as core damage frequency less than 1.0 × 10⁻⁹/module-year and large early release frequency less than 1.0 × 10⁻¹⁰/module-year, and emergency planning zone within nuclear power plant site boundary. All of which is extremely challenging and necessitates innovative safety systems with exceptional reliability. In this context, this study proposed a Flooding Safety System (FSS) as a novel safety system, and its mitigating performance under a hypothetical accident scenario was evaluated by using MELCOR code for validating the efficacy of this conceptual approach. To conduct the accident analysis, a MELCOR input model for the i-SMR was developed. The initiating event assumed was the stuck open of depressurization valve, leading to the discharge of coolant from the primary system into the metal containment vessel, which can be deemed as a loss of coolant accident. The findings in this study revealed that timely operation of the FSS can prevent core damage, thus validating its crucial role to assuring the integrity and reliability of the i-SMR.