Paper Title
Creep-Fatigue Damage Evaluation Using Interrupt Creep Test

Abstract
Grade 91 steel is a candidate material for generation IV nuclear power plant; SFR. The target operating temperature of this application is 550oC, which makes creep-fatigue behavior more significant than generation IIIPWR. However, the G91 creep-fatigue damage diagram provided by ASME has excessive conservatism in it. The blame is on conventional time-fraction testing method which has multiple short comings. First, it is hard to determine the creep-fatigue interaction and microstructural observation is impossible. Second, each loading blocks contains a pair of creep/fatigue cycle which makes it hard to represent actual power plant operation. Hence, an alternative testing method is introduced. The interrupt creep – fatigue test separates those loading blocks into two sets. This makes it easier to determine creep-fatigue interaction as well as to observe the microstructures. The test results suggests that the creep-fatigue damage diagram needs double kink points instead of a single kink point in the previous curve Key Words- Grade91 Steel, Creep-Fatigue, Interrupt Creep Test, Creep-Fatigue Damage Diagram, Sodium Fast Reactor