Strength Analysis Of Steam Generator Nozzle Joint-safety End With Weld Defects

The shell of large container of nuclear island in nuclear power plant is usually made of low alloy steel after rolling or welding, such as the steam generator, the reactor pressure vessel and pressurizer, etc, and different kinds of pipes that are connected to these nuclear containers are usually made of Austenitic stainless steel, so there are many Austenitic steel and low alloy steel welding defects during fabricating nuclear equipments, the organization of dissimilar steel weld is complex, and the welds are difficult to weld.In order to guarantee the quality of the nuclear power equipment, dissimilar steel welding is always performed in equipment supplier. Factory usually welds a stainless steel pipe on the shell(or tube seat), so called joint-safety end of nuclear power equipment.Joint-safety end is a dissimilar steel welding structure of steam generator in the nuclear power plant, the welding quality of joint-safety end is important to the safe running of nuclear power plant.The joint-safety end of newly designed million kilowatt nuclear steam generator, uses nickel base 690 material as filler metal to weld, which material is prone to incomplete fusion in the welding practices. This study takes joint-safety end of million kilowatt nuclear steam generator as analysis object, takes fracture mechanics theory as theoretical basis, according to the method suggested in appendix G of ASME BPVC-XI-2007 section XI - rules for inservice inspection of nuclear power plant components, takes strength analysis of joint-safety end with imaginary weld defects.Firstly, use three-dimensional modeling software Pro/E to establish 3D model of actual structure,then use international used structure analysis software ANSYS ICEM to divide finite element mesh, use ANSYS software to take structure analysis of maximum imaginary defects of different positions of steam generator joint-safety end. and confirm the distribution of mechanical stress and thermal stress at defects area, work out the transient stress intensity factor under corresponding temperature, through comparison with critical stress intensity factor,we can observe that, defects at different positions won't cause structural break under condition of this research subject; under the same structure, the structural instability of operating condition when defects located near the discontinuous structure is worse than when defects located far away from the discontinuous structure, it will cause great harm to nuclear pressure vessel in operating, and this subject will provide guidance in practical manufacturing.