Crack propagation in transition zone of NE Krsko steam generator tubes

Stress corrosion cracks in tube expansion transition region are recognized as one of the major tube degradation problems in operating steam generators. Possibility to predict stable crack propagation during an operational cycle enables adequate maintenance activities. Present report introduces the statistical approach for crack propagation modelling as a possible way to determine the crack propagation model. A NE Krsko specific model has been developed based on nondestructive measurement data and by comparison with large Belgian crack length data base, published in literature. Also, the classification of nondestructive measurement indications is performed, based on the known tube history. Such classification is aimed to help in the determination of most possible time of crack initiation. (author)