Axial strains in fuel cladding associated with creep and fast neutron irradiation

Commercially produced CANDU-PHWR (CaNada Deuterium Uranium-Pressurized Heavy Water Reactor) Zircaloy-4 and Zr-2.5% Nb fuel cladding was biaxially creep-tested in the laboratory and in the WR-1 ractor. The axial strains measured have been interpreted, through a knowledge of the texture, to provide evidence supporting prismatic slip as the major process for axial contraction at high stresses and temperatures and that this is the same process which gives rise to axial lengthening of pressure tubes. At low stresses and temperatures, axial lengthening of fuel cladding appears to be associated with Coble creep in elongated and flattened grains. (orig.)