Eddy Current Position Sensing System for Diverse Safety ROD of PFBR

In Prototype Fast Breeder Reactor (PFBR), Kalpakkam, India, there are three Diverse Safety Rod Drive Mechanisms (DSRDM) in the control plug, which hold the diverse safety rods (DSR). During normal operation, DSR is held outside the active core region by an electromagnet. On receiving Safety Control Rod Accelerated Motion (SCRAM) signal, the electromagnet de-energizes and drops the DSR, which falls under gravity in sodium. The free fall time is required to be monitored during each SCRAM action. An innovative eddy current based position sensor is designed for this purpose. It is not possible for the sensor to have any wired connectivity with the instrumentation. To circumvent this problem an indirect excitation through inductive coupling is incorporated in the design of the sensor. This paper describes the design and testing of the sensor configuration on a one-to-one model. The results have established the feasibility of using inductively coupled eddy current position sensor for DSR in PFBR.