[en] Selected aspects of the development of acoustic monitoring techniques used in fast reactors which are of special interest, or in areas where significant recent advances have been made, are described. The instrumentation techniques discussed include the use of stress wave emission as an early warning indicator of structural failures, the application of high-temperature ultrasonic transducers in hot sodium, detection of cavitation in sodium pumps and of sodium boiling in the core. Vibration of primary tank and pipework, resulting from acoustic emission is under examination and scale models are being used to investigate the vibration modes. (U.K.)