Radiation creep and phase instability of low-activation austenitic steel 12 Cr-20 Mn-W under neutron irradiation in the FFTF fast reactor

Results of a radiation creep experiment conducted in the FFTF fast reactor using the MOTA-2B temperature control facility maintained at ±5°C are presented. Helium-pressurized creep tubes were constructed from a reduced activation austenitic Fe-12 Cr-20 Mn-W steel and irradiated in contact with the sodium coolant. Five hoop stress levels were employed ranging from 0 to 140 MPa. The neutron fluence reached varied from 5.3 to 5.8 × 1022 n/cm2 (E > 0.11 MeV) at target temperatures of 428, 519, and 599°C. The total strains were found to be strongly dependent on irradiation temperature, but not to be completely linear with stress level. The measured stress-free stains are thought to arise from both phase instability and void swelling.