Influence of boron-generated helium on the swelling of neutron irradiated V, V-5Cr and V-5Fe

The effect of He on dimensional stability of V, V-5Cr and V-5Fe alloys has been studied using the B doping technique. The addition of 5 wt% Cr to pure V leads to a significant increase in neutron-induced swelling at 600 C. Although the swelling of V-5Cr increases strongly with irradiation temperature, the influence of Cr is reversed at lower temperatures, with pure V swelling more than V-5Cr. The use of B additions to generate relatively large amounts of He in V, V-5Cr and V-5Fe leads to a very complex swelling response, depending on the B level and the irradiation temperature. At 520 C, B addition is found to increase the cavity density. However, the most pronounced response occurs in V-5Cr at 600 C, where B levels of 100 appm or greater cause a significant reduction in swelling. The complexity of swelling response is thought to result from the competition between He effects and the separate chemical effects of B and Li, each of which may exhibit its own dependence on irradiation temperature. (orig.)