Vanadium alloy as candidate structural material would be used at temperatures ranging above 600°C. However, the components might be exposed to low temperature and low neutron flux irradiation during transient operation such as start-up and shutdown period of the reactor. Helium generation also has a possibility to affect the irradiation behavior of the alloy at the low-temperature. Helium effect on loss of ductility at low-temperature neutron irradiation for vanadium alloy was pointed out from the results of tensile tests using various combinations of helium charging and neutron irradiation. It is possible so far that pre-implantation at ambient temperature increases radiation hardening of the vanadium alloy after irradiation at 400°C. From the viewpoint of low-temperature and low-flux irradiation behavior of vanadium alloy, to clarify the helium effect on microstructure evolution, especially small complexes of interstitial impurity and irradiation defect is needed.
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