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

Abstract

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 ∼10×10−6MPa−1dpa−1 below 500°C and 50–200×10−6MPa−1dpa−1 above 500°C, a value greater than that of commercial V–4Cr–4Ti alloys, austenitic steels and ferritic steels.