Effects of brazing heat treatment on the properties of Zircaloy-4 cladding tube

In manufacturing pressurized heavy water reactor fuel bundles, bearing pads and inter-element spacers are brazed into Zircalloy-4 cladding tube. To investigate the changes of mechanical properties of the cladding tube caused by the brazing, the phase transformation characteristics were studied under the various heat treatment conditions. The rupture characteristics of the brazed cladding tube were studied by the out-of-pile biaxial burst test and biaxial creep rupture test. The effect of brazing on the mechanical anisotropy was studied by the flow surface technique. The critical cooling rates for the different structures could be determined by examining the microstructure: 0.2 deg C/s for the lenticular structure, 2 deg C/s for the parallel plate structure, and 11 deg C/s for the basketweave structure. The failure occurred in the brazed area under the burst deformation test at 400 deg C. However, under the creep test at 400 deg c, the virgin area, i.e., cold worked and stress relieved structure, showed failure. This seems to result from activating of the different slip systems, i.e.,{101-bar0}<12-bar10> in the brazed area and {11-bar01}<112-bar3> and {112-bar1}<112-bar3> in the virgin area, as well as from the different degree of anisotropy. The tensile strength at 400 deg C of the brazed area was higher than the one of the virgin area. (Author)