A perspective on creep and fatigue issues in sodium cooled fast reactors

Development of advanced materials alongwith improved high temperature mechanical properties, particularly creep and fatigue are important and play a major role for the successful development of robust, safe and economical sodium cooled fast reactor (SFR) technology. The components of SFRs operate in demanding environments at high temperatures under complex creep, fatigue and creep-fatigue loading conditions. Based upon the service requirements in terms of different environments, temperature and loading conditions, different materials are chosen for different components. Ti modified 15Cr-15Ni austenitic stainless steel is chosen for clad and wrapper tubes in the reactor core, which experience high fast neutron flux of similar to 10(15) ncm(-2)s(-1) along with high temperatures. Type 316L(N) SS is used for out-of-core structural components like main and inner vessels, and sodium pipelines. For steam generators, modified 9Cr-1Mo steel is chosen for all the components, where liquid sodium and steam/water coexist. Some of the important experiences and exciting achievements in the areas of in-house materials development and its characterization in terms of creep, low cycle fatigue and creep-fatigue properties important to design of reactor components for core, out-of-core and steam generator applications are described in the paper. Future directions for materials research and development activities involving critical issues like radiation damage resistance along with improved mechanical properties for advanced clad and wrapper materials necessary for achieving high fuel burnup and design life up to 60 years for out-of-core structural components leading to economical nuclear energy have been highlighted.