Book Description

The effects of neutron flux and temperature on irradiation creep of 10-mm- diameter Zr-2.5Nb tubes are being assessed in end-of-life experiments in the Osiris reactor in France. The tubes have crystallographic texture, grain shape, and dislocation densities that are similar to those of full-size CANDU reactor pressure tubes. The experiments are performed at nominal operating temperatures of 553 and 583 K in fast neutron fluxes up to 2.0 x 1018 n . m-2 . s-1 (E > 1 MeV). Transverse and axial strains are reported as functions of fluence for specimens internally pressurized to hoop stresses from 0 to 160 MPa and irradiated to fluences up to 1.5 x 1026 and 1.3 x 1026 n . m-2 at 553 and 583 K, respectively. The measured transverse and axial strain rates in these high-fluence experiments are shown to be in good agreement with a creep model relating crystallographic texture to the in-reactor deformation of CANDU pressure tubes. The anisotropy of irradiation creep does not change with fluence, but the temperature dependencies of creep and growth are changing; the activation temperature for creep is increasing, while the magnitude of the activation temperature for irradiation growth (a negative value) is becoming less negative with fluence.