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

Abstract

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 ~ 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.

Motivation for utilizing new high-performance advanced materials in nuclear energy systems

“…Additional research is needed on creep-fatigue synergistic damage mechanisms in irradiated steels [91,92], as well as more detailed studies on mechanical deformation of weldments (in particular Type IV cracking in the heat affected zones) [93,94]. Cyclic fatigue can occur in SFRs due to (low-cycle) start up and shut down transients as well as (high cycle) coolant thermohydraulic instabilities known as "thermal striping" [95,96] and other mechanical vibrations.…”

Larson Miller Parameter for the Prediction of the Creep Life of Unweld and Welded P91 Steel

“…P91 steel is renowned for its used in high-temperature environment such as steam generators in the fossil-fired thermal and nuclear power generation sectors [1][2][3]. P91 steel is made by adding nitrogen (N) to a formula that already contains strong carbide/nitride producing components like vanadium and niobium [4] thus exhibiting superior mechanical qualities at increased temperatures compared to 9Cr-1Mo steel [5][6][7][8]. The most advanced steam power plants attain an efficiency of around 42 percent at steam temperatures of 650°C [9].…”

Thermodynamic Modelling and Microstructural Study of Z-Phase Formation in a Ta-Alloyed Martensitic Steel

“…Martensitic 9–12% Cr steels are widely used high-temperature alloys with excellent stability against corrosion, outstanding creep resistance [ 1 ] and low manufacturing costs [ 2 ] compared to austenitic steels or nickel base alloys. They are reasonably tough, can resist frequent thermal loads [ 3 ] and combine good thermal conductivity with low thermal expansion [ 4 ]. The main fields of application for steel grades such as E911, P91 and P92 today are in turbine parts or surroundings, pipes and boilers or heat exchangers in thermal power plants [ 5 ].…”