Small and medium integral-type reactors are expected for future use as a distric heating system, seawater desalination, small-scale power generation, and ship propulsion. In this study, to investigate the thermal-hydraulic characteristics during natural circulation in an integral reactor, basic single phase natural circulation experiments were done using scaled test facilities of SMART (System-Integrated Modular Advanced ReacTor). Flow distribution through eight steam generator (SG) modules and flow mixing phenomena in downcomer regions were observed. In case of a half-loss of heat sink in 4 out of 8 SG modules, core heat was removed sufficiently by natural circulation and the temeprature distribution at core inlet was uniform. The results were compared with the analysis results using modified RETRAN-03 code. Because these kinds of reactors can be used for nuclear ship reactors, the flow patterns and temperature distributions at inclined conditions were observed. The results show the typical flow characteristics according to the inclined angle. Analytical and experimental results of natural circulation characteristics in this study are expected to provide the important and fundamental design features for the future small and medium integral reactors.
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