Brian V. Cockeram¹, Phil D. Edmondson²; ¹Naval Nuclear Bettis Laboratory, ²Oak Ridge National Laboratory

Atom Probe Tomography (APT) examinations were performed on Zircaloy-2 and Zircaloy-4 following irradiation in the Advance Test Reactor (ATR) to neutron fluences of 2.9-3.1x1025 n/m2 (E>1 MeV). Irradiation at higher temperatures of nominally 410C resulted in about 10-80% less hardening than observed in the literature for irradiations at 260-326C. Clustering of Fe, Sn, and Cr solute at features consistent with the size and shape of loops and line dislocations was observed. These features likely result in the high barrier strength for dislocation loops that correlated with the measured irradiation hardening. Nucleation of isolated clusters of Fe, Sn and Cr were also observed that produce an additional hardening barrier. Local variation in the type and distribution of clusters is observed that is correlated with differences in starting microstructure, precipitates, and local microchemistry,