Development of creep property equations of 316FR stainless steel and Mod.9Cr-1Mo steel for sodium-cooled fast reactor to achieve 60-year design life

Abstract

316FR stainless steel and Mod.9Cr-1Mo steel are candidate structural materials for the present design of sodium-cooled fast reactor (SFR) in Japan. A number of research works have been performed in Japan to develop the SFR for practical use. Aiming at enhancing its economic competitiveness and reducing radioactive waste, Japan Atomic Energy Agency has proposed an attractive plant concept and made great efforts to demonstrate the applicability of some innovative technologies to the plant. One of the most practical means is to extend the design life to 60 years. Accordingly, the material strength standards set by the Japan Society of Mechanical Engineers (JSME) have to be extended from 300,000 to 500,000 hours but this extension requires more precise estimation of creep rupture strength and creep strain of the materials in the long term. This paper describes the development of creep property equations of 316FR stainless steel and Mod.9Cr-1Mo steel considering changes in creep mechanisms at high temperatures in the long term based on evaluations of long-term creep properties of the materials. The creep property equations developed in this study will provide more precise estimation of the creep properties in the long term than the present creep property equations of JSME.Agency (JAEA) has proposed an attractive plant concept and made great efforts to demonstrate the applicability of some innovative technologies to the plant (Kotake et al., 2008). One of the most practical means is to extend the design life to 60 years. Accordingly, the material strength standards set by JSME have to be extended from 300,000 to 500,000 hours but this extension requires more precise estimation of creep rupture strength and creep strain of the materials in the long term. In particular, it is important to accurately estimate creep rupture strength and creep strain at 550°C that is the maximum operating temperature of an SFR.The authors have developed creep property equations based on the evaluations of creep properties of 316FR stainless steel and Mod.9Cr-1Mo steel in the long term. The equations will provide more precise estimation of creep properties of the materials in the long term than the present creep property equations of JSME.