The effect of the Zr oxide layer on the electrochemical dissolution of Zircaloy-4 cladding tubes is examined in LiCl-KCl-ZrCl4 molten salts at 500 degrees C. The cyclic voltammetry of Zircaloy-4 cladding tubes oxidized at 400 degrees C reveals an evident oxidation peak associated with an immediate dissolution of Zr, as also observed in the current transient. In contrast, the Zr oxide layer formed on Zircaloy-4 tubes at 500 degrees C and 600 degrees C significantly inhibits both Zr reduction/oxidation processes on the voltammetric scans in a given potential range. However, the current transients at a constant potential of -0.78 V, where the oxidation of Zr is involved, reveal a dissolution process that is strongly suppressed for an initial period of time proportional to the oxidation temperature, followed by a gradual increase in the dissolution current over time. After the dissolution at -0.78 V for 1 hr, metallic Zr is exposed on a Zircaloy-4 tube oxidized at 500 degrees C, which leads to a recovered current response for Zr reduction/oxidation in the subsequent voltammetric experiments. The XPS results show that the oxide passivation layer is found to be dissolved or removed under high-temperature molten salts. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.031212jes] All rights reserved.