Book Description

Irradiation growth behavior of Zircaloy-2 and -4 was studied on specimens irradiated in the Experimental Breeder Reactor II to fluences of 1.4 to 6.3 x 1025 neutrons (n).m-2 (E > 1 MeV) in the temperature range 644 to 723 K. Measurements in the three principal directions on annealed and cold-worked/stress-relieved Zircaloy-2 slab materials provided evidence that growth is a constant-volume process up to about 680 K. The growth strains were shown to be determined by the crystallographic texture, that is, proportional to (1-3(1-3fdc)), where), where fdc is the fraction of basal poles, is the fraction of basal poles, fc, in the direction d. The growth strains for annealed and cold-worked Zircaloy were large relative to previously reported data, were similar in magnitude, were strongly dependent on irradiation temperature, and varied linearly with fluence over the range investigated. Transmission electron microscopy on annealed Zircaloy-4 specimens revealed a few small voids and larger cavities, a grain boundary second phase, and dislocation loops, tangles, and arrays. The high growth strains in annealed Zircaloy appear to be governed by dislocation arrays formed during irradiation. This implies a change in growth mechanism from that pertaining at lower temperatures in annealed material. The data suggest a transition from saturating steady-state growth at lower temperatures to increasing and eventually high steady-state rates under the conditions of these tests.