Study on Failure Assessment Curves for Safe End of Nuclear Pressure Vessels

In this paper,three-dimensional finite element analysis models are built for the welded safe end of typical nuclear pressure vessels.Through finite element analysis（FEA） of fracture mechanics for the circumferential part-through surface cracks with different sizes in the weld metal,the accurate failure assessment curves（FAC） are constructed according to R6 option 3.The FACs are related to the complex structure of the safe end,the geometry of welding groove,the complex materials at weld joint region of the dissimilar metal and the crack sizes.The FEA results show that with the increase of depth and length of the cracks,the FACs gradually shift down and are close to the R6 option 1 curve,and the FAC of the largest size crack shift down below the option 1 curve.It is concluded that the option 1 curve is overly conservative for shallow and short cracks and non conservative for deep and long cracks.It is suggested that the accurate FACs which are related to crack sizes should be selected for the defect assessment of the safe end.The mechanism that how the crack sizes affect the FACs is also analyzed in this paper.