Development of a Material Strength Standard for Japanese Demonstration Fast Breeder Reactor

This paper discusses about the activities for codification of new structural materials in the Japan Atomic Energy Agency (JAEA) for the Japanese demonstration fast breeder reactor (Hereafter, DFBR), of which operation is presumed to be around 2025. 316FR is to be used for a reactor vessel and internals and Mod.9Cr-1Mo (ASME Gr.91) steel is to be used for primary and secondary coolant circuits, including intermediate heat exchangers and steam generators. 316FR was developed in Japan by optimizing chemical composition within the specifications of SUS316 in the Japanese Industrial Standard which is equivalent to Type 316 stainless steel. The optimization was performed from the viewpoint of maximizing the creep resistance under fast breeder conditions. Mod.9Cr-1Mo steel was developed in Oakridge National Laboratory in the United States. 316FR has not been registered in current codes and standards. Mod.9Cr-1Mo steel is codified in ASTM/ASME, but it has not been registered in current Japanese nuclear codes and standards either. Therefore, it is necessary to include the materials in Japan Society of Mechanical Engineers Design and Construction Code- Part II Fast Breeder Reactors- (Hereafter, JSME FBR Code). Research and development on the two materials were conducted on 1990’s and the result has been summarized as a part of “Draft Demonstration Reactor Design Standard (Hereafter, DDS)”. However, DDS cannot be used for the DFBR as it is for the following reasons. (1)The design life targeted in DDS was 40 years. But the design life of the DFBR is 60 years. (2) Mod.9Cr-1Mo steel was to be used for only steam generators. (3)The design of the DFBR has various innovative features such as compact and simple reactor block, very short piping systems, double-wall-straight tube steam generators and so on. This paper summarized currently available data and information on the above items and shows path forward to the development of a material strength standard for DFBR.