Assessment method for defects of welding joint area at piping safety end of pressure vessel of AP1000 nuclear reactor

Abstract

The invention relates to a high-level assessment method for defects of a welding joint area at a piping safety end of a pressure vessel of an AP1000 nuclear reactor. The method comprises the following steps of: characterizing the detected dimensions of unpenetrated circumferential inner surface defects; establishing a failure assessment graph, wherein the failure assessment graph comprises the family of the failure assessment curves of the unpenetrated circumferential inner surface defects in the different dimensions, which are acquired on the basis of three-dimensional finite element calculation; selecting the failure assessment curves according to the dimensions of the defects; based on the three-dimensional finite element calculation, calculating the family of the curves that stress intensity factors change along an extra resultant bending moment at the deepest points of the unpenetrated circumferential inner surface defects in the different dimensions; determining the stress intensity factors according to the resultant bending moment and the dimensions of the defects; calculating a specific breaking strength parameter Kr; based on the three-dimensional finite element calculation, acquiring the family of the ultimate load bending moment curves of the unpenetrated circumferential inner surface defects in the different dimensions; determining ultimate load bending moments according to the dimensions of the defects; calculating a load ratio parameter Lr; and marking a calculated coordinate (Lr, Kr) on the failure assessment graph, and judging whether falling into an area which is encircled by the selected failure assessment curves, a vertical end line and coordinate axes or not.

Description

technical field [0001] The invention belongs to the technical field of structural integrity assessment, and in particular relates to an advanced assessment method for the circumferential inner surface defect of the dissimilar metal weld seam area at the takeover safety end of the AP1000 third-generation nuclear reactor pressure vessel. It is an advanced assessment method for evaluating and judging the safety of circumferential over-standard defects in the weld zone at the safe end under specified operating conditions. Advanced assessment. Provide accurate technical basis for the safety management and control of nuclear power equipment. Background technique [0002] The dissimilar metal welding joint area at the safety end of the nuclear reactor pressure vessel is a weak link that may fail in the primary circuit. The defects on the inner surface are mainly caused by corrosion, fatigue crack initiation and expansion, which have a great impact on the safe operation of the equi...

AI Technical Summary

Problems solved by technology

Its shortcoming is that the J integral used to construct the failure evaluation curve is calculated by the engineering approximate reference stress method, and the structural limit load at the time of evaluation is calculated by the approximate mechanical analysis method, which is only applicable to simple geometric structures and Loading method, cannot be accurately used to take over complex geometries and complex loads at the safety end

On the other hand, in R6, butt-welded joints are generally simplified into two materials: the base metal and the weld. According to the different positions of the defects in the base metal and the weld, only the mechanical performance parameters of the corresponding materials are used for analysis. The dissimilar metal joint at the safety end of the pipe composed of two kinds of materials (two kinds of welds and two kinds of base metals) cannot be handled accurately

Moreover, the existing higher-level failure assessment diagram method is mainly established for the safety assessment of defects in the second-generation nuclear power equipment in service, and may not be applicable to the structure and materials of the advanced third-generation AP1000 nuclear power equipment currently under construction.

According to literature and patent searches, there is no advanced special method for defect assessment of dissimilar metal welded joints in nuclear power plants at home and abroad.

Images