The natural circulation phenomena occurring in fully integrated nuclear reactors are associated with a unique formation mechanism. The phenomenon results from a structural feature of these reactors involving upward flow from the core, located in the central-bottom region of a single vessel, and downward flow to the steam generator in the annulus region. In this study, to understand the natural circulation in a single vessel involving a multi-layered flow path, single-phase and two-phase natural circulation tests were performed using the SMART-ITL facility, and validation analysis of the TASS/SMR-S code was performed by comparing the corresponding test results. Three single-phase natural circulation tests were sequentially conducted at 15%, 10%, and 5% of full-scaled core-power without RCP operation, following which a two-phase natural circulation test was successively conducted with an artificial discharge of coolant inventory. The simulation capability of the TASS/SMR-S code with respect to the natural circulation phenomena was validated against the test results, and somewhat conservative but reasonably comparative results in terms of overall thermalhydraulic behavior were shown.

在完全集成的核反应堆中发生的自然循环现象与独特的形成机制有关。这种现象是由这些反应堆的结构特征引起的，涉及从位于单个容器的中心底部区域的堆芯向上流动，并向下流动到环空区域的蒸汽发生器。在这项研究中，为了了解涉及多层流路的单个容器中的自然循环，使用 SMART-ITL 设备进行了单相和两相自然循环测试，并对 TASS/SMR-S 进行了验证分析通过比较相应的测试结果来执行代码。在没有 RCP 运行的情况下，在 15%、10% 和 5% 的满量程核心功率下依次进行了三个单相自然循环测试，随后，在人工排放冷却剂存量的情况下，先后进行了两相自然循环试验。TASS/SMR-S 程序对自然循环现象的模拟能力通过测试结果进行了验证，并显示了在整体热工水力行为方面有些保守但合理的比较结果。