Abstract
The recovery of irradiation damage in wrought Zircaloy-2 and Zircaloy-4 was determined following a
series of post-irradiation anneals at temperatures ranging from 343 C to 510 C and for time periods
ranging from 1-h to 500 h. The materials had been irradiated at nominally 358 C in the High Flux
Isotope Reactor (HFIR) at neutron fluences of nominally 3 1025 n/m2 (E > 1 MeV). Irradiation at
nominally 358 C resulted in a coarser distribution of hai loops that result in a 25–45% lower irradiation
hardening than reported in the literature for irradiations at 260–326 C. The irradiation hardening and
recovery were determined using tensile testing at room-temperature. Post-irradiation annealing at
343–427 C was shown to result in an increase in irradiation hardening to values even higher than for
the as-irradiated material in the first 1–10 h of annealing. This Radiation Anneal Hardening (RAH) was
followed by a relatively slow recovery of the irradiation damage. Much faster recovery with no RAH
was observed for post-irradiation annealing at temperatures of 454–510 C. Irradiation at 358 C was
shown to result in different recovery kinetics than observed in the literature for irradiation at
260–326 C. While the general trend described above is true for the four materials tested (alpha-annealed
and beta-treated Zircaloy-2 and Zircaloy-4), notable and yet unexplained differences in RAH and in
recovery are observed between the materials that might be a result of differing solute effects.
Examinations of microstructure using Transmission Electron Microscopy were used to investigate the
RAH and recovery mechanisms. Agreement between the measured and calculated irradiation hardening
using a generalized Orowan hardening model to account for the observed loop structure was not as close
for the post irradiation annealed condition as for the as-irradiated condition, which can likely be
attributed to unaccounted for changes in the configuration of the hai loops to dislocation lines,
segregation of solutes to dislocation loops, and the potential for the formation of fine clusters of point
defects or solutes during annealing.
2015 El