Integrity assessment of steam generator tubes based on elastic-plastic fracture mechanics concept

Operating experience of steam generators in nuclear power plants shows that constituent tubes are affected by diverse degradation mechanisms. The cracked tube can stay in service if sufficient structural margin is assured to preclude the risk of failure. With regard to estimation of the maximum load carrying capacity, most of preceding researches were focused on limit load concept but extensive test data would be needed to endow confidence of the relevant solution. In contrast to this, up to now, integrity assessment scheme based on the elastic-plastic fracture mechanics concept has not been settled despite of its efficiency. In this paper, elastic-plastic finite element analyses of cracked steam generator tubes are carried out. Fracture toughness of the typical tube material is also measured and the crack instability is evaluated by comparing the crack driving force with fracture toughness of the tube material. Analysis results show that the elastic-plastic fracture mechanics method predicts the load carrying capacities accurately compared to the experimental data. Thus, it is anticipated that the elastic-plastic fracture mechanics concept can be applied to integrity assessment of steam generator tubes with through-wall cracks. (author)