The energy security is one of the most critical issues to Japan with scarcity of natural resources, and the long-term energy policies would have to rely on a variety of energy sources limiting the global warming. The integrity of complex huge systems can be materialized only when the perception of various foresightedly potential risks could be repeatedly updated. We aim to establish a quantitative and accurate method for predicting degradation behaviors in structural components in operating plant, such as stainless steels and nickel base alloys. Regarding the material degradation of operating nuclear power reactors, crack growth rate testing of pipe shape specimens are carried out with special emphasis on specimens' geometry and loading conditions to which the structural components of operating plant is subjected. Based on these results, we have been conducting research on the applicability of our crack growth rate prediction model and proposed crack growth rate curves.