Torque Characteristics of the Stepper Motors Used in the Nuclear Reactor Control Rod Drives

Absorber rods, also known as control rods, which regulate the nuclear fuel fission rate depending on their position in the reactor core, are among the most important components of nuclear power facilities. The control rods are moved and positioned by means of electric drives that are part of the reactor control and protection system (CPS). The article discusses inductor stepper motors with electromagnetic excitation of the CPS electric drive. Machines in the nonsalient-pole and salient-pole versions of the stator are compared, and it is concluded that the latter are more advantageous in terms of static and dynamic torques. Based on the model of a stepper motor with a different ratio of the number and width of teeth and slots in the stator and rotor, the motor dynamic mode (making the steps) and static operation mode (fixing the control rod in the specified position) are studied, taking into account the influence of the mechanical load nonlinearity. The calculations were experimentally verified by testing a full-scale prototype made on the basis of a serially produced machine. The results of computational and experimental studies of the torque characteristics of various stepper motor options for the CPS drive are presented. Recommendations are given on the choice of stepper motor tooth zone geometry, which make it possible to improve its torque characteristics in the static and dynamic operation modes.