The integrity of structures behaviour is an important subject for the nuclear reactor safety, specially for components containing a defect under increasing loading. In this case, most of assessment methods are based on the evaluation of the parameter J. This parameter may be difficult to obtain for complex structure like an elbow. Then to avoid complex elastic-plastic finite elements computations of J, a simplified (ie analytical) method has been jointly developped by CEA, EDF and Framatome-ANP. This method, called Js, is based on the reference stress approach and a new KI handbook using elastic stresses determined in the median section of the elbow. To validate this method, a complete set of 3D massive elastic-plastic finite element calculations of J have been performed on elbows (more than 140 calculations are available) for: • different types of longitudinal part-throughwall defect ending on either side of median section: semi-elliptical or long axial defect; • mechanical loading: pressure, bending moment, torsion moment; • different kind of materials: austenitic, ferritic. This paper presents a comparison between the simplified assessment of J and Finite Element results on these configurations for mechanical loading. Then, validity of the method is discussed and an applicability domain is proposed.

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