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 catho dic hydrogen charging method. The optimum conditions for charging more than 1000 ppm of hydrogen was 0.4 A/cm(2) for 24 h at 150 degrees C-0 .5 degrees C in an electrolyte containing hydrobisulphate ions. After vacuum annealing at 400 degrees C for 3 h, thin platelet-shaped hydrid es were formed within the tubing and were preferentially oriented alon g circumferential direction, which was related to the texture of the m aterial. The hydride formed was identified as the delta-ZcH(1.6) and g amma-ZrH phases by X-ray diffraction. The corrosion potential of the h ydrided alloy was +830 mV(SCE) in 90% HNO3 at 25 degrees C and the mat erial was rapidly corroded by anodic polarization. The corrosion poten tial was dramatically decreased in a 20% hydrochloric acid solution co ntaining 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 o f the as-received alloy in the corrosive environments. (C) 1998 Elsevi er Science B.V. All rights reserved.