Development of steam generator tube plugging criteria for axial crack

The operating experience of Korean nuclear power plant shows that the steam generator tubes in alloy 600 are affected by stress corrosion cracking. The cracks, in most cases, are oriented longitudinally and located at the roll transition zone. Literature survey shows that a certain range of through-wall axial crack in steam generator tube can be stayed in service without constituting a safety or reliability problem. Therefore, it is possible to avoid excessive tube plugging by determining the critical crack dimensions which can preclude the risk of tube rupture for steam generator tubes subjected to internal pressure and thermal loading in normal and in accident conditions. In this paper, various evaluations are performed for Korean nuclear unit to determine the plugging criteria based on plastic instability rupture theory and leak-before-break concept