Validation of SAM-NekRS Coupling Against the TALL-3D STH/CFD Coupling Benchmark Transient

Abstract

An important step in nuclear reactor licensing is performing safety analyses and computing the evolution of accident scenarios. Government regulators accept results from System Thermal Hydraulics (STH) codes if within the code's range of validation. When 3D flow effects play an important role in the analyzed transient, an STH code's simplifying 1D assumptions can become inaccurate and even invalid. Computational Fluid Dynamics (CFD) codes can provide more-accurate predictions of complex 3D flow phenomena, but CFD modeling of an entire reactor system remains prohibitively computationally expensive. Therefore, the coupling of CFD with STH codes is an important undertaking. Previously, the authors developed and implemented a domain-overlapping coupling scheme to couple the STH code SAM with the CFD code NekRS, using the coupling tool Cardinal. In SAM-NekRS coupled stability comparisons, the domain-overlapping method showed superior stability behavior compared to the conventional domain-decomposition method. The SAM-NekRS coupling was also validated against a double T-junction 3D scalar mixing experiment, and it was shown that the coupled code resulted in a much better agreement with experimental data than the SAM standalone code. In recent years, the TALL-3D Lead-Bismuth Eutectic (LBE) experimental facility was created for benchmarking STH/CFD coupling efforts. The facility incorporates a test section that contains 3D mixing and thermal stratification, and the benchmark involves a transient from forced circulation to natural circulation, emulating a loss of forced cooling accident. The paper will present both SAM standalone and SAM-NekRS coupled results and will discuss how the results compare to the benchmark's experimental data.