Effect of surface roughness on the oxidization and hydriding behaviour of Zircaloy-4

Fuel cladding tube is one of the most critical parts in the core of a nuclear reactor. It should be manufactured to satisfy very strict clearances and quality requirements. In conventional pressure water reactors like CANDU, Zircaloy-4 is being used for fuel cladding. In the reactor's environment, Deuterium or Hydrogen can ingress and form hydrides in the cladding tube. The hydrogen solubility in α-zirconium decreases dramatically from 6 at.% at 550^oC, to 0.7 at.% at 300^oC, and 10^-4 at.% at room temperature. The excess hydrogen is precipitated in the form of zirconium hydrides. There is no in-depth study of surface roughness effects on the properties of cladding tubes, however surface condition may affect oxidation, hydride formation and mechanical properties. In this study, the effect of surface oxide layer on hydride formation and morphology has been studied. Kinetics of oxidation was measured by TGA in air. It was demonstrated that the surface of oxide layer might act as a protective layer against hydrogen ingress. It has a significant effect on the hydrides morphology. (author)