Application of Acoustic Technique for Surveillance and Anomaly Detection in LMFBRs

Acoustic techniques find wide application in Liquid Metal Fast Breeder Reactors (LMFBRs) for ensuring its high reliability, safety and plant availability. Various surveillance methods based on acoustic technique can be employed in these reactors to detect deviations from normal operating conditions. This could be used for the measurement of drop time of Diverse Safety Rods (DSRs) in the core, detection of in-sodium water leaks in Steam Generators, cavitation detection in sodium pumps and reactor core components. An active R&D program is being pursued in these areas at Indira Gandhi Centre for Atomic Research. Acoustic measurement technique has been used to determine the drop time of Diverse Safety Rods in sodium. 3 nos of Diverse Safety Rods (DSRs) are provided in Prototype Fast Breeder Reactor (PFBR) for its safe shut down in case of a SCRAM. An online drop time measurement system using acoustic technique is planned to detect the proper insertion of DSRs into their corresponding Subassemblies. Experiments were conducted during the performance testing of DSRs in sodium using accelerometer instrumented wave-guide system and free fall time and braking time of DSR have been measured. For detection of in-sodium water leaks in Steam Generators, acoustic method serves as a supplementary monitoring technique with an intermediate sensitivity and instantaneous response. To develop an acoustic leak detection system for Steam Generators of Prototype Fast Breeder Reactor, preliminary studies on the behavior of micro leak and its propagation has been carried out in Sodium Water Reaction Test Rig, injecting steam into sodium. Acoustic technique was employed to characterize the onset of leak. Cavitation in LMFBRs can occur in fuel subassemblies, pressure drop devices, pumps etc. It is important to minimize cavitation to reduce the risk of damage from erosion. Acoustic technique was extensively used in qualifying Prototype Fast Breeder Reactor components against cavitation phenomenon. This paper discusses the various experiments carried out towards the development of the acoustic surveillance methods for FBRs, instrumentation involved, results obtained from experiments and brief details of the future programme.