Numerical analysis of residual stress in the bending process using kinematic isotropic hardening models for a helical tube in SMR and a U-bent tube in PWR

Abstract

This study compares the residual stresses in steam generator tubes used in nuclear reactors—specifically, a U-tube in conventional pressurized water reactor (PWR) and a helical tube in small modular reactors (SMR). With the U-bend radius held constant, tube thickness and helical geometry were varied. Finite element analysis, employing the Yoshida-Uemori kinematic hardening model with Swift isotropic strain hardening law, was conducted to simulate the forming processes and evaluate residual stress distributions. The analysis shows that while the effective strains predicted by pure bending theory closely match the simulation results, differences in plastic deformation and stress evolution arise from the distinct deformation histories. The helical tube exhibits similar residual stresses compared to the U-tube for all thickness and helical geometry, implying that the same heat treatment process may be applicable to both designs. © 2025 Korean Nuclear Society