Creep deformation and rupture behavior of 9Cr-ODS steel cladding tube at high temperatures from 700°C to 1000°C

The Japan Atomic Energy Agency has been developing 9Cr-oxide dispersion strengthened (ODS) steel as a fuel cladding material for sodium-cooled fast reactors (SFRs). Previous studies have formulated the creep rupture equation for 650 degrees C-850 degrees C. However, little data have been obtained above 850 degrees C, and no equation has been formulated. This study conducted creep tests to evaluate creep strength at 700 degrees C-1000 degrees C. Two creep test methods, the internal pressure and ring creep tests under development, were used, and the validation of the ring creep test method was conducted. The results showed that 9Cr-ODS steel undergoes almost no strength change due to the matrix's phase transformation, and a single equation can express a creep rupture strength from 700 degrees C to 1000 degrees C. In validating the ring creep test method, analysis clarified the effect of stress concentration on the specimen. Plastic deformation occurs at high initial stress and may lead to early rupture. The results will be essential for future creep testing and evaluation of neutron-irradiated 9Cr-ODS steel.

Automated summary

This study conducted creep tests on 9Cr-ODS steel and found that a single equation can express creep rupture strength from 700°C to 1000°C. The validation of the ring creep test method was also conducted.