Study on the irradiation mechanical behavior of three-petal fuel rods contact based on multi-physics field coupling

The temperature and velocity fields in the fluid domain are crucial for the analysis of the mechanical properties of three-petal fuel rods (TPFR). Therefore, this study establishes a multi-physics field coupling model of coolant single-phase flow, heat transfer and fuel rods irradiation mechanics using ABAQUS-STAR CCM+. A gap of 0.03 mm is set between the fuel rods to accommodate fluid flow under unirradiated conditions. Subsequently, the thermal parameters are obtained to investigate the stress–strain and deformation distribution, when in contact with adjacent rods. The results indicate that the transverse velocity at different positions is related to the churning effect of the twisted petals. The counterclockwise side of the outer convex arc is affected by the higher-temperature coolant from the inner concave arc region, resulting in a higher heat transfer coefficient. Irradiation enhancement can reduce the risk of plastic deformation, when the burnup reaches 6.59 % fissions of initial metal atoms (FIMA), the maximum strain decreases from 0.0164 to 0.0015. Influenced by the heating power, the fuel rods exhibit non-uniform radial deformation along the axial direction, leading to varying contact states between adjacent rods. Axial elongation of the fuel rods can alleviate stress concentrations in these contact regions.