A study on hydride reorientation of Zircaloy-4 cladding tube under stress

A study of the radial hydride formation in cold worked and stress relieved (CWSR) Zircaloy-4 cladding was performed using a ring tensile method and finite element analysis. Un-irradiated Zircaloy-4 cladding ring specimens charged with hydrogen were tested at various temperatures and loading conditions. Measured threshold stresses at loaded temperatures of 400 °C, 335 °C, 300 °C, and 235 °C turned out to be 60 ± 5 MPa, 68 ± 5 MPa, 75 ± 6 MPa, and 90 ± 6 MPa, respectively, demonstrating the tendency of decreasing threshold stress with increasing temperature. These stresses were lower than previously reported ones and close to the lower bound of collected data from the literature. These results reveal that high temperature preheating seems to affect an initiation of the reorientation. This implies that temperature increase caused by the vacuum drying of spent fuel assemblies for transportation can promote the hydride reorientation, leading to mechanical deterioration of the cladding.