The report summarises the experimental results of 24 uniaxial in-reactor creep tests on various zirconium alloys, covering a range of stresses from 7 to 42 kg/mm2 and temperatures between 200 and 400 °C. At 300 °C increases in creep rate of up to an order of magnitude have been measured in a fast neutron flux of 0.4-1.2 × 1013 n/cm2 · sec (E > 1 MeV) with specimens of cold-worked Zircaloy-2. The flux induced increases were smaller with cold-worked and heat treated Zr-2.5 wt % Nb and not measurable in annealed zirconium. Prior irradiation had no significant effect on creep of Zircaloy-2 and Zr-2.5 wt % Nb in the 10t-7 h range, but significantly reduced the creep rate in the 10t-5 h and higher ranges. The stress dependence of the in-reactor creep rate appears to follow a power law in cold-worked Zircaloy-2 and Zr-2.5 wt % Nb, with a stress exponent of about 3. The temperature dependence of the in-reactor creep rate changes around 350 °C in both cold-worked Zircaloy-2 and heat treated Zr-2.5 wt % Nb. Above 350 °C the dependence can be expressed by an apparent activation energy of 50-60 000 cal/mol, while below 350 °C the activation energy value drops to about 20 000 cal/mol. © 1968.
