Under irradiation, the acceleration of growth of nuclear reactor components made of Zircaloy is clearly correlated to the presence of ⟨c⟩ component dislocation loops. In the early stages, these loops appear to be essentially located close to the intermetallic precipitates. At higher doses, when ⟨c⟩ component dislocation loops are observed all over the microstructure, analysis of the Zr matrix reveals an homogeneous iron content due to the dissolution of the precipitates. Thus, iron may play a significant role in the nucleation of ⟨c⟩ component dislocation loops.
A specific study has been performed on Zircaloy thin foils implanted with increasing amounts of iron. The conditions of nucleation and growth of these ⟨c⟩ component dislocation loops have been followed in a 1-MeV transmission electron microscope. The dose level for ⟨c⟩ component dislocation loop nucleation is weakly Fe-content dependent. However, their size and density increase with increasing iron implantation. These results are compared to direct observations made on irradiated reactor components. The role of iron on accelerated growth is then discussed.