Irradiation creep behavior of V–4Cr–4Ti alloys irradiated in a liquid sodium environment at the JOYO fast reactor

Irradiation experiments on V–4Cr–4Ti alloys with sodium-enclosed irradiation capsules in the JOYO fast reactor were conducted using pressurized creep tubes (PCTs). The irradiation creep strain was significantly larger than the thermal creep strain below 686 °C, but there was no swelling of the neutron-irradiated V–4Cr–4Ti alloys. At temperatures below 500 °C, the irradiation creep was found to be proportional to the square root of the neutron dose and linear with the stress level. Above 500 °C, it was expected to be proportional to the stress level to a power greater than unity, because the irradiation creep mechanism could change from the stress-induced preferred absorption mechanism (SIPA) to the preferred absorption glide mechanism (PGA). By comparing annealed PCT specimens with cold-worked specimens, the cold-worked V–4Cr–4Ti alloys exhibited a larger irradiation creep strain compared with the annealed alloys. The irradiation creep compliance of the V–4Cr–4Ti alloys were ∼10 × 10−6 MPa−1 dpa−1 below 500 °C and 50–200 × 10−6 MPa−1 dpa−1 above 500 °C, a value greater than that of commercial V–4Cr–4Ti alloys, austenitic steels and ferritic steels.