Analysis of static and transient behavior of nested electromagnetic clutch in small modular reactors

Small modular reactors (SMRs) are vital for expanding nuclear energy use and mitigating climate change, yet suitable electromagnetic clutches for their control systems remain insufficiently developed. To address this gap, this study develops a compact nested electromagnetic clutch with an outer diameter of only 66 mm—significantly smaller than traditional designs used in PWR, MRX, and DRX systems—and establishes a comprehensive analytical framework integrating experimental testing, two-dimensional (2D) magneto-mechanical coupling finite element modeling, and three-dimensional (3D) magneto-thermal-mechanical coupling simulations. The electromagnetic force characteristics were experimentally measured and used to validate the numerical models, with discrepancies maintained within 25% for steady-state force–current relationships and within 10% for coil-position–dependent force variations. The 2D and 3D simulations consistently reproduced the magnetic flux density, magnetic field strength, and magnetic flux distributions, confirming the accuracy of the modeling approach. The proposed clutch exhibits a maximum electromagnetic force of 11.6 N and demonstrates nonlinear parabolic relationships with respect to current and coil position. 3D simulations further show that structural deformation remains small and the maximum von Mises stress (131.09 MPa) stays within safe limits even under reactor-relevant thermal conditions. Overall, the results verify that the proposed compact electromagnetic clutch satisfies the operational, spatial, and mechanical requirements of SMR environments and offers a reliable basis for future CRDM miniaturization and optimization.