Fluid flow in a diametrally expanded CANDU fuel channel – Part 2: Computational study

The current work presents investigations of flow through a 37-element CANDU nuclear fuel bundle residing within a deformed pressure tube. This scenario simulates the long-term effects of aging, whereby the pressure tube may experience up to ̃6% diametral creep, resulting in flow bypass and the concomitant increase in fuel temperature due to local undercooling. This work examines in high spatial detail the three-dimensional, three-component fluid velocity field through the fuel channel. A companion paper is dedicated to the experimental component of this work, which is based on Magnetic Resonance Velocimetry. In the present paper, computational fluid dynamic simulations have been performed with hydra using an implicit large eddy simulation to predict turbulent flow behavior. Together, an improved understanding has been gained in quantifying flow bypass, the evolution of geometry-induced inter-subchannel mixing, and various turbulent effects, such as recirculation, swirl, and separated flow. These capabilities are not possible with conventional experimental techniques or thermal-hydraulic codes. The overall goal of the combined works is to continue developing experimental and computational capabilities for future investigations to support nuclear reactor performance and safety.