Dislocation Substructure in Zirconium Alloys Irradiated in EBR-II

Abstract

The dislocation microstructures of annealed Zircaloy-2, cold-worked Zr-2.5 wt% Nb and extruded Excel (Zr-3.5 wt% Sn-0.8 wt% Nb-0.8 wt% Mo) neutron irradiated in EBR-II at 670 to 690 K to fluences of 1.7 to 6.3 x 10/sup 25/ n/m/sup 2/ (E>1 MeV) and also of cold-worked Zr-2.5 wt% Nb irradiated to 1.2 x 10/sup 25/ n/m/sup 2/ (E>1 MeV) at 550 K in Unit 4 of Pickering Nuclear Generating Station are reported. The irradiation damage produced in zirconium alloys by fast neutron irradiation in EBR-II at 657 to 675 K consists of type dislocation loops and, in annealed Zircaloy, component dislocations. Both type and component dislocations survive fast neutron irradiation to relatively high fluences (5.5 x 10/sup 25/ n/m/sup 2/ at 657 K). Cold-worked Zr-2.5 wt% Nb irradiated in Pickering-4 to 1.2 x 10/sup 25/ n/m/sup 2/ at 550 K contains fine type loops and residual component dislocations from cold-work. All zirconium alloys exhibiting high (non-saturating) irradiation growth rates contain type dislocations and type loops. The presence of component dislocations is also inferred. This suggests a modified model of irradiation growth in which vacancies segregate to component dislocations or faulted loops and interstitials to type loops.