Manufacturability and strength assessment of modified 9Cr-1Mo steel products for Japan sodium cooled fast reactor components, 2; Long thin-walled tubes with small diameter

Wakai, Takashi ; Onizawa, Takashi  ; Obara, Satoshi; Nakashima, Takashi*; Yokoyama, Tetsuo*; Iseda, Atsuro*; Ogumo, Shinya*; Futagami, Satoshi*  

To enhance the economic competitiveness, high-Cr ferritic steels are adopted as the structural materials for JSFR, because the steels have both excellent high temperature strength and thermal properties. Among the high-Cr ferritic steels, modified 9Cr-1Mo steel (compatible to ASTM A213 T91) is a candidate of the structural material for the demonstration facility of JSFR, because the steel has superior microstructure stability at elevated temperature for long time. As for the steam generator tubes, to enhance the safety, straight double-walled tubes will be employed. In this study, the following technical issues were investigated; (1) Industrial manufacturability of thin-walled small bore tubes made of modified 9Cr-1Mo steel, (2) performance demonstration of the thin-walled small bore tubes, (3) industrial manufacturability of double-walled tubes using the thin-walled small bore tubes and (4) extraction of technical problems to manufacture the double-walled tubes for the JSFR steam generator. As a result, thin-walled small bore tubes made of modified 9Cr-1Mo steel were successfully manufactured by using the existing industrial facilities, up to 17m in length. The mechanical properties of the tubes satisfy the requirements from plant designing, as well as those from the material strength standards. Further, double walled tubes were also manufactured, up to 15m in length. The surface conditions of the tubes and the contact pressure between inner and outer tubes should be optimized.