Irradiation-induced dimensional changes in polycrystalline iodide zirconium and zircaloy-2

Growth experiments have been performed up to a fast neutron dose of 4.2.1025 neutrons (n)/m2 on polycrystalline iodide zirconium specimens of differing texture, grain size, and dislocation densities at 353 and 553 K. Rapid attenuation of growth occurs in annealed material above a dose of 6.1024 n/m2 at 353 K while only weak dose and texture dependences of growth are observed in similar material at 553 K. Effects of texture and grain size on growth at both temperatures have been interpreted in terms of postulated changes in the irradiation-induced damage structures at these temperatures. Comparison of growth data on polycrystalline iodide zirconium with published data on annealed Zircaloy-2 indicates that solute tin atom trapping is effective in enhancing low dose growth followed by rapid growth saturation at 353 K. The importance of a preexisting dislocation structure in permitting growth to continue unattenuated with dose at 353 K is shown in growth data obtained on as-received coldworked iodide zirconium. Finally, the possibility of breakaway growth occurring in polycrystalline iodide zirconium at 353 and 553 K is discussed in the light of recently published data on annealed Zircaloy-2