Numerical simulation of temperature field of reactor control rod drive mechanism

Control Rod Driver Machining (CRDM) is one of the most important components in reactor internals. The increase of temperature due to the heat generated by the current in the CRDM coils in operation and that transferred by the internal high-temperature coolant may result in aging or even failure of CRDM structures. Three-dimensional numerical simulation of the external flow field of the ACP100 integrated head assembly and CRDM bundles at different environment temperature was carried out. The obtained air temperature and convective heat transfer coefficients of CRDM were then applied to a single CRDM as outer boundary condition, and detailed thermo-fluid-solid coupling analysis was performed by considering the internal natural convection flow of coolant. Numerical results indicate that there is noticeable temperature gradient along the CRDM axial direction from interior to exterior. Among lift, movable gripper and stationary gripper coils, the highest temperature is observed in the stationary gripper coils but is less than the admissible temperature of CRDM coils at various environmental temperature. The proposed CRDM temperature field analysis method and the numerical results provide useful reference and guidance for the structural design and reliability evaluation of the CRDM in the future.