Preliminary Assessment of Cooling Performance in Small Modular Reactor Metal Containment Vessel according to the Filling Gas Types.

Abstract

As an innovative feature of small modular reactors (SMRs), SMRs have employed a metal containment vessel (MCV) surrounding a reactor pressure vessel (RPV). According to the double-vessel structure, a gap is formed between MCV and RPV. The atmospheric condition of the gap is maintained either by filling it with inert gases or by creating a vacuum to prevent heat loss in normal operation and to enhance the reactor safety in a transient state. In particular, the type of inert gases in the gap affects the condensation performance within the SMRs. However, as research on analyzing condensation performance under mixed environments of inert gas and steam in the gap during accident situations is insufficient, further studies are needed. Thus, this study focused on evaluating the condensation performance within the MCV under different gap-filling gases, including argon, nitrogen, and vacuum. The experiment was conducted under transient conditions simulating scenarios such as automatic depressurization valve (ADV) operation. Experimental setup and conditions were established based on preliminary studies utilizing MELCOR and computational fluid dynamics (CFD) codes. Our findings indicate that the vacuum gap exhibited superior cooling performance compared to other non-condensable gases (NCGs). While our study provides valuable insights, it is essential to acknowledge its limitations, including experiments and a defined test matrix based on calculations. Overall, this research will contribute to understanding heat transfer mechanisms and optimizing cooling performance in SMRs, advancing their development across various applications.