In nuclear power plants (NPPs), one of the important yet uncertain phenomena during a station blackout (SBO) accident is the possibility for a counter-current natural circulation flow in the reactor coolant system (RCS) pressure boundary, which could divert the core melt progression and/or the in-vessel fission product (FP) distribution and, in turn, lead to a heatup and eventual creep rupture. From the risk and accident management points of view, one of key concerns is to predict more explicitly whether such a creep rupture can occur in the RCS pressure boundary, and if it indeed can, also predict the most probable time and the most likely location. This paper presents plant-specific analysis results on the potential characteristics of natural circulation-induced creep rupture of the RCS pressure boundary that could potentially take place during an SBO accident of a reference pressurized water reactor (APR1400). MELCOR-CFD (Computational Fluid Dynamics) coupled analysis was performed to determine more precisely the relevant physical parameter that could greatly influence on the behaviour of natural circulation and the ensuing creep rupture. Multiple sensitivity analyses were also carried out to investigate the influence that particular MELCOR modeling schemes and plant conditions have in estimating the RCS creep rupture characteristics. The analysis results and relevant insights were summarized in terms of particular points of interest.

在核电厂 (NPP) 中，核电站停电 (SBO) 事故期间重要但不确定的现象之一是反应堆冷却剂系统 (RCS) 压力边界中可能出现逆流自然循环流，这可能会使堆芯转移熔体进展和/或容器内裂变产物 (FP) 分布，进而导致升温和最终蠕变破裂。从风险和事故管理的角度来看，关键问题之一是更明确地预测这种蠕变破裂是否会在 RCS 压力边界内发生，如果确实发生，还要预测最可能的时间和最可能的位置。本文介绍了在参考压水反应堆 (APR1400) 的 SBO 事故期间可能发生的自然循环引起的 RCS 压力边界蠕变破裂的潜在特性的特定工厂分析结果。执行 MELCOR-CFD（计算流体动力学）耦合分析以更精确地确定可能对自然循环行为和随后的蠕变破裂产生重大影响的相关物理参数。还进行了多重敏感性分析，以研究特定 MELCOR 建模方案和工厂条件对估计 RCS 蠕变破裂特性的影响。分析结果和相关见解根据特定的兴趣点进行了总结。