A two-phase natural circulation test using SMART integral test loop (SMART–ITL) was conducted to explore thermo-hydraulic phenomena of two-phase natural circulation in the SMART reactor. Specifically, the test examined the natural circulation in the primary loop under a stepwise coolant inventory loss while keeping the core power constant at 5% of the scaled full power. Based on the test results, three flow regimes were observed: single-phase natural circulation (SPNC), two-phase natural circulation (TPNC), and boiler–condenser natural circulation (BCNC). The flow rate remained steady in the SPNC, slightly increased in the TPNC, and dropped abruptly and maintained in the BCNC. Using a natural circulation flow map, the natural circulation characteristic in the SMART–ITL was compared with those in pressurized water reactor simulators. In the SMART–ITL, a BCNC regime appeared instead of siphon condensation and reflux condensation regimes because of the use of once-through steam generators.

使用 SMART 整体测试回路 (SMART-ITL) 进行了两相自然循环测试，以探索 SMART 反应器中两相自然循环的热工水力现象。具体来说，该测试检查了在逐步冷却剂库存损失下主回路中的自然循环，同时保持核心功率恒定在缩放全功率的 5%。根据测试结果，观察到三种流态：单相自然循环（SPNC）、两相自然循环（TPNC）和锅炉-冷凝器自然循环（BCNC）。SPNC 流量保持稳定，TPNC 流量略有增加，BCNC 流量急剧下降并保持不变。使用自然循环流图，将 SMART-ITL 中的自然循环特性与压水反应堆模拟器中的自然循环特性进行了比较。