The consequences of liquid entrainment through the fourth stage Automatic Depressurization System (ADS-4) of Advanced Passive nuclear power reactor (AP1000) are decreased reactor core coolant inventory and increased resistance to quick depressurization of the reactor primary coolant system. Therefore, the accurate knowledge of the Onset of Liquid Entrainment (OLE) is critical to nuclear reactor safety (NRS) assessment. In this study, three-dimensional computational fluid dynamics (CFD) simulations of OLE were carried out using a two-fluid Eulerian model of ANSYS Fluent CFD code along with the renormalization group (RNG) $\mathrm{\kappa }-\mathrm{\epsilon }$ turbulence model for each phase. In OLE phenomena, the interfacial drag has a significant effect but available choices of interfacial drag coefficient in Fluent were not suitable due to the presence of droplet clusters in entrainment. Therefore, a modified interfacial drag coefficient accounting for droplet clusters was used. The transient simulations were performed with this modified CFD model and validated against ADS-4 Depressurization and Entrainment TEst Loop (ADETEL) data. The comparison between CFD calculations and experimental data shows a good agreement. Furthermore, the effects of the liquid mass flow rates and single inlet on OLE were also investigated with the validated CFD model. To improve the understanding of OLE phenomena, the liquid volume fraction and gas velocity field distributions were also studied.

通过先进无源核动力反应堆（AP1000）的第四级自动减压系统（ADS-4）夹带液体的后果是反应堆堆芯冷却剂存量减少和反应堆主冷却剂系统快速减压的阻力增加。因此，准确了解液体夹带 (OLE) 的发生对于核反应堆安全 (NRS) 评估至关重要。在本研究中，使用 ANSYS Fluent CFD 代码的两流体欧拉模型以及重整化组 (RNG) 对 OLE 进行了三维计算流体动力学 (CFD) 模拟$\mathrm{\kappa }——\mathrm{\epsilon }$每个阶段的湍流模型。在 OLE 现象中，界面阻力具有显着影响，但由于夹带中存在液滴簇，因此 Fluent 中可用的界面阻力系数选择并不合适。因此，使用了考虑液滴簇的改进的界面阻力系数。瞬态模拟是使用这种修改后的 CFD 模型进行的，并根据 ADS-4 减压和夹带测试回路 (ADETEL) 数据进行了验证。CFD 计算与实验数据之间的比较显示出良好的一致性。此外，还使用经过验证的 CFD 模型研究了液体质量流量和单入口对 OLE 的影响。为了提高对 OLE 现象的理解，还研究了液体体积分数和气体速度场分布。