Material strength evaluation for 60 years design in Japanese sodium fast reactor

Nagae, Yuji ; Onizawa, Takashi  ; Takaya, Shigeru  ; Yamashita, Takuya  

316FR and Mod.9Cr-1Mo steels are candidates as structural materials for Japanese Sodium Fast Reactor, JSFR. The design life and operation temperature of JSFR is 60 years and 823K, respectively. Time-dependent allowable stress is essential. The evaluation of allowable stresses to 500,000 h is a considerable item. Long term strength is evaluated from a viewpoint of microstructural evaluation related to fracture mechanism. In addition, degradation after long term operation at elevated temperature is important. Aging is considered as one of the degradation. The effect of aging on short term property is analyzed. Material strength standard is also necessary for very thick tube sheets of forgings and small diameter thin walled seamless pipes, which are made of Mod.9Cr-1Mo steel in steam generators. This paper summarized currently available data and information on the above items, and shows path forward to the development of material strength standard for 60 years design in JSFR.