LOW-TEMPERATURE IRRADIATION CREEP OF FUSION-REACTOR STRUCTURAL-MATERIALS

Irradiation creep has been investigated in the Oak Ridge Research Reactor in an assembly spectrally tailored to achieve a He:dpa ratio of 12-14:1 appm/dpa in austenitic stainless steels. Temperatures of 60-400-degrees-C were investigated to address the requirements of near term fusion devices. It was found that austenitic alloys, especially PCA, have higher creep rates at 60-degrees-C than at 330 and 400-degrees-C. Since this phenomenon could not be explained by existing theoretical models, a new mechanism was proposed and a corresponding theoretical model was developed. Since vacancy migration times can be a few orders of magnitude longer than the irradiation times in this temperature regime, the immobile vacancies do not cancel climb produced by mobile interstitials absorbed at dislocations. The result is a high climb rate independent of stress-induced preferred absorption (SIPA) mechanisms. Preliminary calculations indicate that this mechanism coupled with preferred-absorption-driven glide at higher temperatures predicts a high creep rate at low temperatures and a weak temperature dependence of irradiation creep over the entire temperature range investigated.