Computational fluid dynamic investigations of flow bypass through an aged CANDU pressure tube

Single-phase, isothermal computational fluid dynamics simulations of a whole CANada Deuterium Uranium (CANDUTM) channel with twelve simplified CANDU 37M fuel bundles were performed with Hydra. Both as-received and aged pressure tubes were considered in this work. The aged pressure tube geometry considered asymmetric sag and diametral expansion profiles with a maximum sag of 57 mm and a maximum diametral expansion of 5.2%. The predicted fluid velocity and turbulent kinetic energy obtained from the two cases were compared in order to predict the impact of pressure tube deformation (sag and diametral expansion) on coolant flow. The boundary conditions and material properties are representative of normal operating conditions in a high-powered channel of the Darlington Nuclear Generating Station. It has been determined that pressure tube deformation has a significant impact on coolant flow behaviour, whereby up to 27% of flow bypasses the fuel.