Abstract In modern nuclear risk analysis for external-flooding scenarios, Computational Fluid Dynamics (CFD) tools are used to simulate the generation, propagation, and interactions of Nuclear Power Plants (NPPs) with the nuclear Systems, Structures, and Components (SSCs). Smoothed Particle Hydrodynamics (SPH), as a Lagrangian and mesh-free method, is one of the particle-based CFD methods. Since SPH methods can effectively handling large-scale fluid simulations with complex interfacial structures, SPH-based software has been used to simulate the impacts of external flood onto nuclear facilities, and the simulation results have been used to support nuclear safety analysis. However, previous risk analysis assumes that SPH methods and the corresponding simulation packages are applicable to the external-hazards risk analysis, and their simulation uncertainties do not affect the confidence of safety decision. Considering the high consequences to nuclear safety induced by simulation errors, a systematic and complete validation process is needed to evaluate the adequacy of SPH simulations in informing related safety decisions. In this study, a scoping-stage assessment is performed for SPH’s adequacy in simulating the real-scale external flooding scenarios, especially in predicting the surface-wave impacts on SSCs at NPP sites. To ensure the completeness and consistency, validation frameworks, Code Scalability Applicability and Uncertainty (CSAU), and its regulatory guide, Evaluation Model Development and Assessment Process (EMDAP) are followed to guide validation activities and to make final code adequacy assessment. First, an external-flooding scenario is designed, and SPH simulations are performed with an SPH-based software named Neutrino. A Phenomenon Identification and Ranking Table (PIRT) is created, and the surface-wave impacts are identified as one of the high-rank phenomena. At the same time, a performance measurement standard is created for measuring the code adequacy in informing safety decisions consistently and transparently. Next, numerical benchmarks are designed for assessing the code adequacy of SPH methods and corresponding software implementations on Neutrino. Next, code accuracy is evaluated by comparing simulation results from Neutrino against experimental measurements in each benchmark. Meanwhile, a scaling analysis is performed to determine a group of dimensionless number for characterizing important physics and to assess the applicability of validation database collected in reduced-scale facility to the prototypic scenario. Finally, results from all activities are brought together to make an adequacy decision. It is found that, based on the current evidence, SPH methods and associated Neutrino software can predict the unbroken surface-wave peak pressure onto stationary rigid with reasonable accuracy if the suggested sizes of particles are used. However, it is suggested by independent reviews that the validity of major assumptions in target applications need to be evaluated with large-scale experiments, and the relevancy of other phenomena like turbulence and air pockets need to be identified with more benchmarks. As for the SPH’s adequacy in predicting the impact forces on dynamic rigid, the available evidence is not sufficient to support the decisions.

中文翻译：

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用于模拟外部洪水情景的平滑粒子流体动力学方法的充分性评估

摘要 在外溢情景的现代核风险分析中，计算流体动力学 (CFD) 工具用于模拟核电厂 (NPP) 与核系统、结构和组件 (SSC) 的生成、传播和相互作用。平滑粒子流体动力学 (SPH) 作为一种拉格朗日和无网格方法，是基于粒子的 CFD 方法之一。由于SPH方法可以有效处理复杂界面结构的大规模流体模拟，基于SPH的软件已被用于模拟外部洪水对核设施的影响，并将模拟结果用于支持核安全分析。然而，先前的风险分析假设 SPH 方法和相应的模拟包适用于外部危害风险分析，它们的模拟不确定性不影响安全决策的置信度。考虑到模拟错误对核安全造成的严重后果，需要一个系统和完整的验证过程来评估 SPH 模拟在为相关安全决策提供信息方面的充分性。在这项研究中，对 SPH 在模拟实际规模外部洪水情景方面的充分性进行了范围界定阶段评估，特别是在预测表面波对核电厂站点 SSC 的影响方面。为确保完整性和一致性，遵循验证框架、代码可扩展性适用性和不确定性 (CSAU) 及其监管指南、评估模型开发和评估过程 (EMDAP) 来指导验证活动并进行最终的代码充分性评估。首先，设计了一个外部洪水场景，和 SPH 模拟使用名为 Neutrino 的基于 SPH 的软件进行。创建了现象识别和排序表 (PIRT)，并将表面波影响识别为高级现象之一。同时，创建了一个性能测量标准，用于测量代码在一致和透明地通知安全决策方面的充分性。接下来，设计数值基准来评估 SPH 方法和相应软件在 Neutrino 上实现的代码充分性。接下来，通过将 Neutrino 的模拟结果与每个基准中的实验测量值进行比较来评估代码准确性。同时，进行比例分析以确定一组用于表征重要物理的无量纲数，并评估在缩小规模的设施中收集的验证数据库对原型场景的适用性。最后，将所有活动的结果汇总在一起以做出充分性决定。发现，根据目前的证据，如果使用建议的粒子尺寸，SPH 方法和相关的 Neutrino 软件可以以合理的精度预测不间断的表面波峰值压力到固定刚性上。然而，独立评论建议，需要通过大规模实验评估目标应用中主要假设的有效性，需要通过更多基准来确定湍流和气穴等其他现象的相关性。