Development of Advanced Turbulent Flow Simulation Techniques for Use in Nuclear Reactor Safety Analysis, 20-R9680

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Principal Investigators
Kaushik Das
Debashis Basu
Scott Painter
Lane Howard
Steve Green

Inclusive Dates:  01/01/07 – Current

Background - Currently the design, safety analyses, and accident simulations for nuclear reactors rely primarily on one-dimensional, system-level codes. These system-level codes rely significantly on correlations to resolve complex phenomena like thermal mixing, cross flow and turbulence, which are often encountered in complex fuel bundle geometries. Rapid advances in computational fluid dynamics (CFD) make it feasible to analyze reactor components by solving the full Navier-Stokes equations. This reduces dependence on empirical correlations and provides a more accurate spatial and temporal description of the system. However, modeling issues like turbulence remain to be adequately resolved before accurate results can be obtained with reasonable computing resources. SwRI researchers are exploring existing turbulence models as well as developing some advanced multiscale turbulence models for application to reactor core channel flow characterized by pulsation, secondary flows and unsteadiness.

Approach - Existing commercial CFD solvers are used to simulate mass flow and energy transport with turbulence models such as the traditional k-ε, k-ω, renormalization group k-ε, and the large eddy simulation (LES) models. Previous studies have shown that the Reynolds Averaged Navier-Stokes (RANS) representations of turbulence fail to capture the desired unsteadiness and other flow physics and the high-fidelity LES models are computationally expensive. Hybrid multiscale turbulence models like Detached Eddy Simulation (DES) are a promising new approach that strikes a balance between the traditional RANS-type formulation and the LES techniques. These multiscale models provide a better representation of turbulence than commercial solvers and could be readily implemented by customizing and extending the already implemented models in the solvers. The present work has developed multiscale models to simulate flow and transport in a single rod-channel configuration, a sector of a multiple rod-channel configuration and advanced reactor geometries.

Accomplishments - A number of well-established turbulence models for fuel rod configurations have been tested. The unsteady data obtained using the single-rod geometry is analyzed to understand the frequency contents of the signal. Flow over packed rod bundles resembling the lower plenum flow in a gas-cooled reactor has been simulated and results compared with the experimental observations. A number of multiscale DES models have been developed and benchmarked against standard flow configurations. These models are being applied to different rod-channel configurations to assess their effectiveness in simulating flow and transport in reactor components.

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