Abstract
It is necessary to evaluate the fracture load limit of structures in a nuclear power plant in case of severe accidents. Recently, a numerical simulation using GTN (Gurson-Tvergaard-Needleman) model has been applied to a structural model to simulate the ductile fracture behavior. This model considers the microscopic ductile-fracture process and simulates the nucleation, growth, and coalescence of voids. However, it has been just applied to the evaluation for small and simple geometries such as pipe and flat plate specimen with cracks. In this study, the applicability of the fracture analysis method using GTN model for a large scale structure was examined. Fracture analysis was performed by creating a reduced model for the internal pressure test of a steel containment vessel. High equivalent plastic strain and void volume fraction were observed at the fracture point of the welded part along the equipment loading hatch as the internal pressure increased. However, no fracture was observed, which was different from the test result. Considering that increase in the void volume fraction is affected by the stress condition, an additional analysis with revised structural conditions was performed. On the assumption that there was a discrepancy in the welded joints, the welded joint structure was partly modified. As a result, penetration and crack propagation was observed along the welded part at the equipment loading hatch and drywell, which was similar to the test results. It is concluded that the GTN model is effective to evaluate the fracture behavior of large scale structures.
