Overview of SCWR candidate materials stress corrosion tests

Slow strain rate tests on several SCWR candidate materials were done over the last 10 years at VTT. The test materials were austenitic stainless steels with 15-23% Cr and 10-15% Ni and oxide dispersion strengthened ferritic/martensitic steels with 12-20% Cr. The tests were performed in supercritical water at 250 bar in the temperature range of 500-650oC with 100-150 ppb dissolved oxygen. With regards to the stress corrosion susceptibility and ductility, the best performer in the tests was AISI 316L steel. On the other hand, large heat to heat variation can be expected: another heat of 316L was very susceptible to intergranular stress corrosion cracking. DL-EPR test revealed that at least some heats of low carbon 316 are subject to fast thermal sensitisation at 550oC in supercritical water.