Thick crystalline zirconium oxide films were synthesized on Zircaloy-4 substrates by anodic oxidation at room temperature in NaOH solution with a stable applied voltage (300 V). The film is approximately 4.7 mu m in thickness. The XPS and SEM analysis shows that the film is a three-layer structure in water, hydroxide and oxide parts. The thickness of that order is similar to 0.01 mu m, similar to 1 mu m, similar to 3.7 mu m, respectively. The oxide layer is composed of tetragonal and monoclinic phases with the volume ratio about 0.2. Furthermore, the thick anodic film acts as a barrier to oxygen and zirconium migrations. It effectively protects zirconium alloys against the worse corrosion. An extremely low passive current density of similar to 0.018 mu A/cm(2) and a low oxidation weight gain of similar to 0.411 mg/cm(2) were also observed in the films. (c) 2005 Elsevier B.V. All rights reserved.