The use of acoustic emission methods as aids to the structural integrity assessment of nuclear power plants

Since it is an integral method permitting continuous monitoring and remote defect location, acoustic emission offers promising benefits for the nuclear industry. Particular potential applications relating to the integrity of the primary pressure boundary of nuclear reactors that are considered in this report are the detection of flaws during pre-service and requalification hydrotests, and continuous monitoring for crack growth and leakage.The correlations between fracture mechanics and acoustic emission are discussed on the basis of certain fundamentals of material emission behaviour. The influence of instrumentation and of aspects related to wave propagation on the detectability and evaluation of acoustic emission signals is considered.The conclusion reached is that at the present time acoustic emission can be used predominantly during hydrotests as a search method for cracks. Although some degree of characterization and sizing of defects may be obtained on the basis of empirical data, a quantitative evaluation of defect severity based on fracture mechanics cannot yet be made satisfactorily. It is expected that a considerable improvement in this respect may be achieved by applying a transfer correction that takes into account the depth position and directivity pattern of the source.The technique of leak detection by acoustic emission shows promising results permitting the location and quantification of leaks. Practical experience and future research work are expected to enhance the accuracy and detection sensitivity.