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The irradiation growth behavior of annealed polycrystalline Zircaloy-2 has been investigated in the DIDO reactor at Harwell at fluences up to 1 x 1025 neutrons (n)m-2 (E > 1 MeV) and in the temperature range 513 to 673 K. Growth strain data for two batches of rolled, annealed Zircaloy plate did not obey the G ? (1 - 3f) texture relationship with transverse direction specimens (f = 0.25 and f = 0.35) exhibiting negative growth following an initial positive transient. The effect of irradiation temperature on growth was not marked over the range studied except that, at 673 K, growth strains appeared to saturate at low fluences. Apart from this, longitudinal and transverse growth strains decreased slightly with increasing temperature above 573 K. Specimens of large grained, ?-annealed Zircaloy with a completely random structure showed virtually no sensitivity of growth to either fluence or temperature under the conditions studied. The apparently anomalous growth behavior of the transverse annealed plate materials cannot be explained by the influence of density changes during growth. It is proposed that the deviation from the expected growth-texture relationship is due to the effects of intergranular stresses which occur as a result of, and in opposition to, irradiation growth in polycrystalline materials.
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.
Accelerating irradiation growth has been reported for several zirconium alloys with a range of metallurgical states during high-temperature tests in fast-breeder reactors (673 to 723 K) for annealed Zircaloys in thermal test reactors at power reactor temperatures (523 to 623 K) and in power reactor core components fabricated from annealed or recrystallized Zircaloy. In the latter case, there was a transition from low to high irradiation growth rates at moderate fluences (about 3 x 1025 n/m2, E > 1 MeV, at 580 K) related to the nucleation and growth of basal plane c-component loops.
Experimental investigation of irradiation growth on annealed Zircaloy-4 and 20% to 50% cold-worked Zr-2.5wt%Nb specimens with stress relief has been carried out. The specimens are irradiated in a heavy water reactor at 610 K to 4.2 x 1024 n/m2 (E > 1.0 MeV). The growth strains increase linearly with fluence. The saturation of growth is not observed for all specimens. The difference of growth behavior between two kinds of Zircaloy-4 tube may be associated with the content of minor alloying elements and impurities that influence the microstructure evolution under irradiation.