Design characteristics of nuclear steam supply system and passive safety system for Innovative Small Modular Reactor (i-SMR)

In response to the growing global climate crisis, nuclear power, particularly through small modular reactors (SMRs), is emerging as a potential solution for sustainable energy production. This paper presents an innovative SMR (i-SMR) design being developed in the Republic of Korea, which integrates proven technologies from existing pressurized water reactors while emphasizing enhanced safety, cost-effectiveness, and operational flexibility. The i-SMR features a fully passive safety system, achieving a core damage frequency of 1E-9, thus significantly reducing the necessity for public evacuation during potential accidents. The i-SMR design incorporates several key elements, including a boron-free operation, a helical coil steam generator, an in-vessel control rod drive mechanism, and a canned-motor reactor coolant pump within an integrated nuclear steam supply system. This paper explores the design characteristics and the detailed operating mechanism of the passive safety system, comprising the passive emergency core cooling system, passive auxiliary feedwater system, and passive containment cooling system. Safety performance analyses were conducted for a loss-of-coolant accident using the Multi-dimensional Analysis of Reactor Safety (MARS) code. The analysis results demonstrate the performance and the thermal-hydraulic behavior of the passive safety system with key phenomena affecting the performance.