Hydride formation by high temperature cathodic hydrogen charging method and its effect on the corrosion behavior of Zircaloy-4 tubes in acid solution

Zircaloy-4 cladding tube was hydrided using the high temperature cathodic hydrogen charging method. The optimum conditions for charging more than 1000 ppm of hydrogen was 0.4 A/cm2 for 24 h at 150°C–0.5°C in an electrolyte containing hydrobisulphate ions. After vacuum annealing at 400°C for 3 h, thin platelet-shaped hydrides were formed within the tubing and were preferentially oriented along circumferential direction, which was related to the texture of the material. The hydride formed was identified as the δ-ZcH1.6 and γ-ZrH phases by X-ray diffraction. The corrosion potential of the hydrided alloy was +830 mVSCE in 90% HNO3 at 25°C and the material was rapidly corroded by anodic polarization. The corrosion potential was dramatically decreased in a 20% hydrochloric acid solution containing small amount of a strong oxidizer, such as ferric ion due to the instability of the passive film on zirconium in this environment. The corrosion potentials of the hydrided alloy were lower than those of the as-received alloy in the corrosive environments.