The Influence of Fuel Bundle Misalignment and Pressure Tube Aging on Mass Flow Rate Distribution in CANDU Fuel Channels

This work presents a numerical investigation of a CANDU fuel channel using Computational fluid dynamics (CFD) methodology. The developed CFD model is employed to examine the impact of bundles misalignment and pressure tube aging on mass flow rate distribution in CANDU fuel channels. Practically, in the station, the bundles in the channel are introduced without any specific alignment, resulting in endless potential misalignment configurations. This work focuses on three distinct misalignment configurations, with two of them representing the most challenging scenarios (A & B) in terms of flow obstruction and creating a convoluted twisted flow path, while the third scenario (C) allows for a continuous flow path in-between the fuel rods. All configurations were examined at the designed pressure tube diameter with no aging and compared to the perfectly aligned fuel bundle case. To study the aging effect, the same model was used while incorporating axial variation in pressure tube diameter. The results indicated that fuel bundles misalignment can lead to a reduction in mass flow rate ranging from -6% to -16%, depending on the misalignment configuration. Conversely, the pressure tube aging resulted in a 9% increase in the mass flow rate. This increase was primarily attributed to a nearly doubled clearance between the fuel bundles outer diameter and the inner diameter of the pressure tube. The outcome of this analysis provides an insight into parameters that might influence the flow rate inside fuel channels.