Limit load analysis for local wall-thinning steam generator tubes

Steam generator(SG) tubes form approximately 80% of pressure boundary of the reactor primary coolant[1]. During the past 40 years, a large number of operating PWPs have experienced degradation due to local wall-thinning of SG tubes, which was caused by corrosion or squeezing of tubes at support plate or tubesheet intersections or other reasons. This paper introduced the study of experiment and numerical analyses for plastic limit loads of local wall-thinning SG tubes. The effect of the dimension of local wall-thinning on plastic limit load was analyzed. The main contents in this paper were summarized as follows: 1 Experiment equipment which could test not only bursting pressure but also plastic limit load was built. Two kinds of local wall-thinning shapes were respectively made on SG tubes. One kind of local wall-thinning shape was rectangle-like flaw, which was used to simulate local wall-thinning caused by squeezing of tubes at support plate. The other kind of local wall-thinning shape was arc-like flaw, which was used to simulate local wall-thinning caused by corrosion. Different size local wall-thinning SG tubes of these two kinds of shape were test by using the equipment. 2 Regularization method for local wall-thinning defect was provided based on experimental and finite element method. 3 The effect order of local wall-thinning configuration on plastic limit load was studied. It was found that: Except defect thickness, the longitudinal length and circumferential length of SGT defect can also influence the plastic limit load; When the longitudinal length of SGT defect exceeded 6 mm, the effect of longitudinal length on plastic limit load can be ignored; When the circumferential angle of defect exceed 45 degree, the effect of circumferential angle on plastic limit load can be ignored. (authors)