Creep specimens made from cold-worked Zr-2.5Nb tubes, fabricated with two different microstructures and crystallographic textures, were irradiated in the Osiris reactor in France in a fast neutron flux of about 1.8 × 1018 n ∙ m-2 ∙ s-1, E > 1 MeV, at 553 and 585 K. The hoop stresses from internal pressurization range from 0 to 160 MPa. The basal poles were oriented in the radial-transverse plane of the tubes, either about 30° from the radial direction or primarily in the transverse direction; these are similar to the crystallographic textures in fuel sheathing and in CANDU reactor pressure tubes. Dislocation densities were similar while grain size and shape differ significantly.
The creep specimens were irradiated to fast neutron faiences up to 7 × 1025 n ∙ m-2. Creep rates were obtained from strain versus fluence plots and creep compliances were obtained from plots of the strain rates against hoop stress for each material at each temperature. The ratio of creep rates at the nominal temperature of 583 K to those at 553 K was similar to that derived from stress relaxation results at temperatures between 523 and 568 K.
The ratio of the biaxial creep compliance in the axial direction to that in the transverse directions is different for the two test materials; 0.0 to -0.1 for the fuel sheathing texture and 0.6 to 0.7 for the pressure tube texture. The results were analyzed using a self-consistent model developed previously to account for the contributions to the creep anisotropy of the three microstructure parameters involved here and for the grain interaction effects. The model, which was normalized to other test reactor and power reactor creep data for cold-worked Zr-2.5Nb tubes, predicted the ratio of the creep compliances to be -0.26 and 0.63, respectively. Thus, in agreement with previous conclusions, the creep anisotropy of Zr-2.5Nb tubes with pressure-tube-like crystallographic texture can be adequately predicted.