Verification of the Output Signal Change of Control Rod Position Indicator at the End of Its Life Time Available to Purchase

The system-integrated reactor currently under development at the Korea Atomic Energy Research Institute is being designed with a soluble boron-free operation and the use of a nuclear heating for the reactor start-up. The Control Element Drive Mechanism (CEDM) for the integral reactor is designed to raise and lower the control rod in steps of 2mm in order to satisfy the design features of the integral reactor which are the soluble boron-free operation and the use of a nuclear heating for the reactor start-up. The actual position of the control rod could be achieved to sense the magnet connected to the control rod by the position indicator around the upper pressure housing of CEDM. It is sufficient that the actual position information of the control rod at a 20mm interval from the position indicator is used for the core safety analysis. As the magnet moves upward along the position indicator assembly from the bottom to the top in the upper pressure housing, the output voltage increases linearly step-wise at 0.2VDC increments. Between every step, there are transient areas which occur by a contact closing of three reed switches, which is the 2-3-2 contact closing sequence. In this paper the output voltage signal corresponding to the position of the control rod is expected as the 2-1-2 contact closing sequence due to the aging of the magnet at the end of its life time. We verify that the output signal change at the end of the life time of the position indicator could not affect the operational performance of the position indicator. Also it is found that the voltage divider network for the output signal of the position indicator is designed to be robust and reliable during the aging process.