Zircaloys are widely used as the cladding materials of light water reactors(LWRs).They present good mechanical properties and workability,with a remarkable corrosion resistance.In recent years,hydrogen behavior in the nuclear fuel cladding aroused researchers attention for the reason that the working life of the fuel cladding is dependent of the oxidation of Zirconium alloys involving hydrogen absorption through the oxide film.In this work,hydrogen absorption and the permeation behavior of the passive layer formed on Zircaloy-4 were investigated.Potentiostatic and potentiodynamic polarization,Mott-Schottky analysis,and electrochemical impedance spectroscopy,leakage current as well as FESEM and Raman scattering spectroscopy were employed to characterize the passive defects before and after hydrogen permeation.It was found that the nanoscale passive ZrO2 films play great importance in the resistance against corrosion; hydrogen impingement,however,reduced the passive impedance towards hydrothermal oxidation.The increase of defects(vacancies)in passive films was probably attributed to the degradation,as demonstrated from the testing of dopant concentration and current leakage.We believe that this finding will provide valuable insight in the understanding of the corrosion mechanism of zircaloys used in LWRs.