Computational fluid dynamics investigations of the impact of CANDU fuel bundle rotational misalignment on flow behaviour and fuel temperatures

CANDU reactors have fuel channels consisting of 12-13 CANDU fuel bundles, and the rotational angle of each fuel bundle is not controlled when it is loaded into the channel. Coolant behaviour, which may be affected by bundle rotational misalignment, can influence fuel performance; however, the degree of this impact is not yet well understood. This work performed Computational Fluid Dynamics (CFD) simulations with heat transfer using STAR CCM+ on two CANDU 37M fuel bundles with four different rotational misalignment angles (0°, 20°, 40°, and 60°). By comparing the predicted coolant behaviour and fuel temperature profiles, it has been determined that misalignment can alter subchannel mass flow rates by over 40% and increase the maximum fuel temperature by approximately 20 °C. This study also investigates the physical mechanisms by which a misaligned endplate affects these outcomes, through a detailed examination of coolant flow behaviour in the endplate region. • CFD simulations with heat transfer of CANDU 37M fuel bundles with rotational misalignment. • Misalignment changes subchannel mass flow rates by over 40%. • Maximum fuel temperature changed by ∼ 20 °C with bundle misalignment. • Endplate misalignment mechanisms analysed through detailed flow study.