To evaluate the integrity of a structure is to prove its ability to perform its mechanical functions for all modes of loading, normal or accidental, and throughout its life. In the context of the nuclear safety, for the most important structures such as the tank or the primary circuit, the presence of a degradation in these structures grouping several aspects, such as cracks created during welding. We seek then, to show the mechanical resistance for this defect mode. It also seeks to fit the mechanical resistance of a structure in the presence of a crack when the defects have been detected during an inspection. In this context, the fracture mechanics provides the necessary tools to analyze cracked components. Its purpose is to establish a fracture criterion to foreordain the loading margins in normal or accidental operating conditions. Each type of rupture must be the subject of a specific characterization.

The modeling of the welding is desirable to guess the deformation of the components during manufacture, the position and the magnitude of maximum residual stresses and to envisage metallurgical effects in specific zones. The welding are problems of complex modeling requiring the thermal and structural solutions. This has to lead to the development of several software packages and codes for simulation by finite elements. The welding condition, the properties of the structure and their interactions have significant influences on the thermal and structural responses (temperature history, distortion, and residual stress) in welded structures. This paper presents a finite element procedure for the prediction of welding-induced residual stresses and distortions. Comparison is made with tow numerical example. The first example is a butt welded joint of two plates, while the second is a Cruciform welded joint of two plates with four passes. Moreover, a comparison between the Cruciform weld and the butt-weld which we can obtain the parameters of the linear fracture mechanics; stress intensity factor K and energy release rate G.