Applicability of Reed Switch Type Rod Position Indicator for a Nuclear Reactor

Control rod drive mechanism is an electromechanical equipment that provides linear movement to a control rod assembly to control the reactivity of a nuclear reactor. The rod position indication system for the SMART control rod drive mechanism provides a position signal of a control rod assembly. It is an electric circuit consisting of reed switches and precision resistors installed at regular intervals. Because the reed switch manufacturer arranges the magnetic properties of the reed switch in Ampere-Turns and it is an uncomfortable dimension for an analytical estimation, it is not easy for the reed switch users to estimate the operability of a reed switch application at the design stage. Furthermore, this dimension is not standardized among the manufacturers. The performance of a reed switch application needs to be analytically verified to reduce the development risk. The operability of a reed switch application has been proved to be affected by the electromagnetic field generated around the application or an adjacent reed switch itself. Thus, it is necessary to have an effective means for a reed switch operability analysis at the design stage because the operating magnetic properties from the manufacture may not be applicable for a numerical analysis. In this paper, a new analysis methodology for a reed switch operability is proposed, and the feasibility is discussed for the rod position indication system.