Natural Circulation Test and Non-Condensable Gas Effect on a Two-Phase Thermosyphon Loop

Abstract

Despite the increasing demand for electricity, as the use of fossil fuels is minimized to prevent climate change, nuclear systems can be a reasonable electrical power source in the near future. Particularly SMRs with improved safety and public acceptance due to small-size and their passive containment cooling systems are considered realistic options. Among SMRs, light-water reactor generates hydrogen during postulated accidents because steam reacted with zircaloy, and the steam and accumulated hydrogen are discharged from a pressure vessel into a containment initially filled with a non-condensable gas such as air. The steam condensed on the containment wall and transferred heat by condensation to the outsider water pool should be clarified to ensure reactor safety. If high spatial resolution temperature distribution can be obtained when condensation occurs on the wall, it is possible to more accurately predict the condensation heat transfer phenomenon in the accident scenario described. In this study, a condensation test of a naturally circulated two-phase thermosyphon loop was performed using an optical fiber sensor that can measure distributed temperature information with high spatial resolution. The experimental results obtained through the dedicatedly designed test facility have been reasonably analyzed especially for the effect of non-condensable gas, and the results will be used for computer code development and verification. © 2023 Proceedings of the 20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2023. All rights reserved.