Development of high-chromium steel for sodium-cooled fast reactor in Japan and creep-fatigue assessment of the steel

Wakai, Takashi ; Sukekawa, Masayuki*; Date, Shingo*; Asayama, Tai ; Aoto, Kazumi ; Kubo, Shigenobu* 

This paper presents the provisional material specification and characteristics of the high chromium (Cr) steel for the sodium-cooled fast reactor (SFR) in Japan and creep-fatigue assessment of the steel. Based on the mechanical test and metallurgical examination results, it is clarified that tungsten (W) should be diminished to achieve better ductility and toughness. Then the provisional specifications of the high Cr steel for SFR components are proposed. Material characteristics, e.g. cyclic stress-strain relationship and creep strain curve, are also presented based on the material test results. Using these characteristics, a creep-fatigue strength assessment of the steel was performed. Conservative predictions were obtained and it was clarified that such conservativeness were resulted from over estimation of creep damage caused by too large initial stress at the beginning of dwell. It can be pointed out there are some rooms for improvement in the assessment procedure.