Limit load analyses of helical coiled steam generator tubes with a volumetric flaw

Maintaining structural integrity of piping has always been an important effort in the nuclear power industry. To resolve piping issues such as unanticipated failures caused by diverse planar and volumetric flaws, several guidelines were developed and used especially for assessment of steam generator tubes. However, because the major components of new reactors have dissimilar geometric features and loading conditions compared with those of conventional operating reactors, most of existing assessment methods are not expected to be applicable; therefore, new alternative assessment guidelines are required. In this paper, a systematic structural integrity assessment of helical coiled steam generator tubes for a small and medium modular reactor, which is currently being designed, is introduced. Three-dimensional detailed finite element (FE) limit analyses have been carried out to simulate the behaviours of the tube containing a volumetric flaw such as elliptical wear-type, rectangular wear-type and tapered wear-type defects subjected to external pressure. Failure pressures were calculated from the FE analyses by changing defect depth, defect length and defect angle affecting the load-carrying capacity of the tube. Thereby, engineering equations were developed as a function of these key parameters to predict structural failures and system reliability to enable more reasonable design and manufacturing decisions.