Although one of the main problems of the power quality is voltage sag in nuclear installations, the terminology used for the compensation devices is different. A Thyristor switched capacitor control is one of the equipment for voltage disturbance mitigation. This paper suggests a Thyristor Switched Capacitor control for mitigation of voltage sag in nuclear research reactor as a sensitive load. Performance of the proposed control investigated under different types of voltage sag magnitudes and is modeled using the user-defined dynamic modeling (UDM) tools in ETAP. The results show appropriate operation of the proposed control system to examine the developed technique.