This paper describes experimental and analytical works to confirm that the design standard for Sodium cooled Fast Reactor (SFR) components sufficiently covers possible failure mechanisms. Present design standards for SFR components have been proposed by Japan Society of Mechanical Engineers (JSME). For economical reasons, Mod.9Cr-1Mo ferritic steel, equivalent to ASME Gr.91, will be widely adopted to coolant systems in future SFRs. Creep-fatigue damage evaluation method in JSME design standard for SFR components has been constructed based on experiments and/or numerical analyses of conventional austenitic stainless steels, such as 304SS. Since the material characteristics of Mod.9Cr-1Mo steel are substantially different from those of austenitic stainless steels, it is required to verify the applicability of the design standards to the SFR components made of Mod.9Cr-1Mo steel. However, few structural test data exist to verify the applicability of the conventional design standards. Therefore, to investigate creep-fatigue failure aspect of the several types of structural discontinuities, a series of uni-axial creep-fatigue tests were conducted using double-ended notch bar specimens made of Mod.9Cr-1Mo steel under displacement controlled condition with 30 minute holding. In these tests, imposed axial displacement was controlled to result in 0.7% axial strain range at the minimum section area. The curvature radii of the specimens were 1.6 mm, 11.2 mm and 40.0 mm. The specimen having 1.6 mm notch and 11.2 mm notch failed from outer surface but the specimen having 40.0 mm notch showed obvious internal crack nucleation. In addition, though total duration time of the creep-fatigue test was only 2,000 hours, a lot of creep voids and inter granular crack growth were observed. To clarify the cause of such peculiar failure, some additional experiments were performed, as well as some numerical analyses. We could point out that such a peculiar failure aspect might result from corresponding stress distribution in the cross section. Since radial temperature distribution resulted from high-frequency induction heating and local multiaxiality also might produce such peculiar failure, analytical investigations were carried out. As a result of a series of investigations, possible causes of such peculiar failure could be narrowed down. A future investigation plan was proposed to clarify the most significant cause.
