Adequacy evaluation of smoothed particle hydrodynamics methods for simulating the external-flooding scenario

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.