Failure Assessment Diagram in Structural Integrity Analysis of Steam Generator Tubes

The assessment of the structural integrity of Steam Generator Tubes (SGTs) in nuclear power plants has been receiving increasing attention in the literature in the last years due to the negative impact related to their failures. Diverse failure prediction methodologies were proposed in the past to ensure tube integrity by fulfilling regulatory authorities’ requirements. They have lead however to overly conservative plugging or repairing criteria like the so-called “40% criterion”. In the present work, in line with modern approaches, an alternative more realistic methodology based on the Failure Assessment Diagram (FAD) is proposed. With that purpose, different studies available in the literature dealing with the experimental determination of fracture toughness of SGT materials were firstly reviewed. Using the results reported in these researches, the FAD was used for predicting the failure modes (i.e., ductile fracture or plastic collapse) of defective SGTs for varied crack geometries and loading conditions. The present analysis indicates the potentiality of the FAD as a comprehensive methodology for predicting the failure loads and failure modes of flawed SGTs.