Effects of Endcaps and Spacer Pads on Unsteady Fluid Forces and Flow Through a 37-Element CANDU Fuel Bundle

Unsteady fluid forces acting on CANDU fuel bundles inside a pressure tube are an important source that induces bundle vibration during operation. In this study, a comprehensive three-dimensional computational fluid dynamics (CFD) model is presented to investigate unsteady coolant flow through a 37-element CANDU fuel bundle in a pressure tube. The CFD model includes all fuel elements with endcaps and spacer pads and two endplates. Large eddy simulation is employed to solve the complex CFD model. Time histories and frequency spectra of unsteady fluid forces acting on individual components and the fuel bundle are predicted. Fluid velocities and flow development after the upstream endplate and spacer pads are also investigated. The effects of the spacer pads and endcaps on the mean value and standard deviation of unsteady fluid forces and flow characteristics are predicted.