Acoustic Technique for Diverse Safety Rod Drop Time Measurement in PFBR

Diverse safety rods (DSRs) are used in Prototype Fast Breeder Reactor (PFBR) to shutdown the reactor during emergency conditions (SCRAM). These rods contain neutron absorber materials to reduce the reactivity for the safe shutdown of the reactor. During normal operation of the reactor, DSRs are held above the active core using electromagnets. During a SCRAM the electro-magnets are de-energized and DSR falls into the core. Since it is a safety related action, no active system is used for driving the rods into the core and the rod falls under gravity force. It is required to measure the fall time of DSR during each SCRAM in the reactor to ensure proper insertion of the DSR in the core. Experiments were carried out in various facilities to develop a measurement technique. This paper discusses the details of Diverse Safety Rod Drive Mechanism (DSRDM), acoustic technique used for fall time measurement, experiments carried out, analytical modeling details and its results and conclusion.