Study on safety margins assessment practices

This study concerns Finnish safety factor definitions applied to structural integrity analyses of nuclear power plant (NPP) piping components. On global level, International Atomic Energy Agency (IAEA) provides information and definitions on safety margins and safety factors of NPP components. In Finland, the significant documents concerning the safety factors of NPP components are YVL Guides. However, they do not give the actual safety factor data, but instead refer to certain applicable standards. These are mainly ASME code Sections III and XI. Both deterministic and probabilistic crack growth analyses were performed for two representative BWR piping components. For comparison purposes, the analyses were carried out both with and without safety factors. Due to various kinds of safety factors and conservative assumptions, it is difficult/ impossible to define what is the total safety margin of a structure or component. Structural integrity analyses of structures and components would benefit from such more specific definitions of safety factors that would give a more accurate assessment of the total safety.