Irradiation creep of the US heat 832665 of V-4Cr-4Ti

Full text of publication follows: Significant progress has been made in developing vanadium alloys for fusion energy applications. The uncertainty in irradiation creep of these alloys is still a major issue due to a limited database. A few previous irradiation experiments were performed on the reference alloy V-4Cr-4Ti between 200 and 500 deg. C up to 6 dpa, and there was a significant inconsistency in creep strain rate at high stress levels. A bilinear creep behavior of V-4Cr-4Ti observed in the BR-10 experiment was not found in the ATR-A1 and HFIR 12J irradiation experiments. Additional irradiation creep data are needed to resolve this uncertainty. There is also lack of irradiation creep data at higher temperatures and high fluences to evaluate the performance limit of this alloy. This paper presents the creep data of the US Heat 832665 of V-4Cr-4Ti in the recently completed HFIR RB17J irradiation experiment. In this experiment, pressurized creep tubes of two heats of V-4Cr-4Ti, i.e. US Heat 832665 and NIFS Heat-2 were included in the 425 and 600 deg. C lithium-containing capsules irradiated to 3.7 dpa. Creep deformation was characterized by measuring the changes of a tube diameter before and after irradiation. It was found that the creep strain rate of the US Heat 832665 exhibited a linear relationship with the effective stress up to 180 MPa at 425 deg. C. At 600 deg. C the creep compliance for V-4Cr-4Ti increased significantly and non-linear stress dependence was observed above 120 MPa, where thermal creep is expected to dominate. The irradiation creep data of the US Heat 832665 in the HFIR RB17J experiment are compared with those of the same heat from the lithium-containing capsules irradiated at 200 and 300 deg. C in the ATR-A1, and from the helium-containing capsules irradiated at 500 deg. C in the HFIR 12J. The dependence of stress, temperature, neutron flux and environment of the creep strain rate is evaluated and discussed. The irradiation creep data are also compared with the thermal creep data of V-4Cr-4Ti in lithium to differentiate the contribution of thermal creep and irradiation creep. The irradiation creep data are critical in assessing the performance limit of vanadium alloys and understanding the influence of important variables such as crystal structure on irradiation creep. The research was sponsored by the Office of Fusion Energy Sciences, the U.S. Department of Energy under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC. (authors)