Benchmarking Computational Fluid Dynamics for Application to PWR Fuel

Abstract

The present study demonstrates a process used to develop confidence in Computational Fluid Dynamics (CFD) as a tool to investigate flow and temperature distributions in a PWR fuel bundle. The velocity and temperature fields produced by a mixing spacer grid of a PWR fuel assembly are quite complex. Before using CFD to evaluate these flow fields, a rigorous benchmarking effort should be performed to ensure that reasonable results are obtained. Westinghouse has developed a method to quantitatively benchmark CFD tools against data at conditions representative of the PWR. Several measurements in a 5×5 rod bundle were performed. Lateral flowfield testing employed visualization techniques and Particle Image Velocimetry (PIV). Heat transfer testing involved measurements of the single-phase heat transfer coefficient downstream of the spacer grid. These test results were used to compare with CFD predictions. Among the parameters optimized in the CFD models based on this comparison with data include computational mesh, turbulence model, and boundary conditions. As an outcome of this effort, a methodology was developed for CFD modeling that provides confidence in the numerical results.

Phenomenological investigations on the turbulent flow structures in a rod bundle array with mixing devices

“…Al. [8] have demonstrated a process used to develop confidence in CFD as a tool to investigate the flow and temperature distributions in a rod bundle array with spacer grids. They performed thermal hydraulic experiments in a 5x5 rod bundle array with mixing vanes by using the PIV system and a heater rod.…”

CFD methodology and validation for single-phase flow in PWR fuel assemblies

“…The mesh, turbulence model, computational domain, and boundary conditions were used to improve the CFD prediction versus the test data. The final CFD model showed reasonable agreement versus the test data (Smith, 2002). With confidence established between the CFD model methodology and test data, application of CFD modeling was extended to PWR conditions, which are at higher temperature and Reynolds number versus the benchmark data.…”

“…As noted in Smith (2002), average parameters such as pressure drop across a 500 mm axial rod bundle span (including a grid) and average turbulent intensity have been compared in prior models showing good agreement between CFD and test data. For this paper, local comparisons of lateral flow field and heat transfer will be provided.…”

“…The applicability of turbulence models to the simulation of fuel rod bundles has been tested and validated by Westinghouse in their extensive research (Smith, 2002), and the renormalization group (RNG) k-ε model (Yakhot, 1992) had been found to produce the closest agreement with available experimental data. The improvement in the prediction obtained with the RNG model is assumed to be related to the somewhat inherited sensitivity to curvature and rotation contained in its turbulence dissipation rate equation.…”

Validation for CFD Simulation in Rod Bundles With Split-Vane Spacer Grids Based on LDA Measurement

“…Krauss et al investigated large-scale quasi-periodic fluctuations in the enlarged tight-lattice bundles based on the three dimensional (3D) flow measurement utilizing the hot-wire probe with x-wire (Krauss and Meyer, 1998;McClusky, 2004) employed the particle image velocimetry (PIV) to measure the cross flow induced by split mixing vane in one of the subchannels in the 5 × 5 rod bundle. With their experimental data, Smith III et al validated their CFD methodology (Smith et al, 2002). Dominguez-Ontiveros et al (2012) utilized the two-dimensional time-resolved PIV (2D TR-PIV) to measure the flow field in a 5 × 5 rod bundle with spacer grid.…”