Determination of Feasible Design Ranges for the Passive Emergency Core Cooling System of a Small Modular Reactor Under LOCA Conditions

초록

Following the increasing emphasis on passive safety in nuclear reactor design, a small modular reactor (SMR) with fully passive safety systems is currently under development in the Rep. of Korea. In this SMR, the passive emergency core cooling system (PECCS) plays a critical role in mitigating loss of coolant accident (LOCA) scenarios through reactor depressurization and coolant recirculation. While previous studies have primarily focused on overall system responses under representative accident conditions, systematic investigations on the influence of key PECCS design parameters and the determination of their feasible design ranges remain limited. To address this, the present study aims to identify feasible design ranges for key PECCS parameters that ensure reliable accident mitigation performance. A surrogate modeling approach based on Gaussian process regression (GPR) is developed using a database generated from MARS-KS simulations to enable efficient exploration of the design space. In addition, a global sensitivity analysis using Sobol indices is performed to quantify the relative importance of each parameter and their interaction effects. The results indicate that the depressurization valve diameter is the dominant parameter governing accident mitigation performance, significantly affecting both core cooling and reactor depressurization behavior. Feasible design regions are then identified by simultaneously applying core integrity and containment integrity criteria, defined by the minimum reactor vessel (RV) water level and the maximum containment vessel (CV) pressure, respectively. Overall, the applied approach facilitates the systematic identification of design conditions that satisfy multiple safety requirements and may provide useful insights for the design of passive safety systems in SMRs.