Large Eddy Simulation of TALL-3D Facility Using Spectral Element Method

The pool-type design of advanced metal-cooled reactors offers several significant benefits, including reduced risk of coolant leaks, simplified structural design, and enhanced passive safety. In particular, the primary coolant is contained within a large pool, which minimizes the potential for leaks and provides an extra barrier against sodium leakage. This configuration allows for a more compact primary system, reducing the overall size of the reactor while also enhancing safety through substantial thermal inertia; the large volume of coolant acts as an immense heat sink, enabling passive decay heat removal via natural circulation even in the event of system failures. The TALL-3D liquid-metal facility was introduced to support these advancements as part of the SESAME project (Simulations and Experiments for the Safety Assessment of MEtal-cooled reactors). In this study, Large Eddy Simulation (LES) is performed using the GPU-accelerated spectral element code NekRS to investigate the forced and natural convection operational conditions of the TALL-3D facility. Two Conjugate Heat Transfer (CHT) cases have been performed: forced convection and natural convection. The overlapping mesh methodology (NekNek) framework in NekRS is employed to couple multiple subdomains with distinct mesh configurations, enabling interaction through boundary conditions. NekNek simulations usually involve multiple Message Passing Interface (MPI) ranks, with each session assigned a unique communicator, allowing for independent fluid-thermal simulations. These sessions can vary in polynomial orders, physical models, and time-stepping, providing accuracy and efficiency in simulation configurations. The temperature field simulation results data were compared with experimental measurements, demonstrating good agreement across all operational conditions of interest.