Nickel-based alloys 182,600 and 52 were exposed to simulated Pressurized Water Reactor (PWR) primary water (1000 ppm B, 2 ppm Li, O-2 <10 ppb, 325 degrees C) under different dissolved hydrogen (DH) conditions [0,2, 25 and 50 cm(3) H-2(STP) kg(-1)] for times up to 1 month in a recirculating autoclave. The influence of exposure time and DH on oxide films formed on the alloys was evaluated by means of electrochemical tests; electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S). The in situ EIS was performed every day, allowing the monitoring of the oxide layer formation and change. M-S was performed at room temperature after the full exposure time. The results showed that the maximum in the defect concentrations obtained via M-S analysis and the maximum crack growth rate are at the same DH content, thus relating electrochemical testing to stress corrosion cracking observations. A conceptual separation between the electrochemical behavior of (1) the oxide layer (visible in the higher frequencies of EIS) and (2) the oxide layer - solution interface (visible in the lower frequencies of EIS) was able to explain the effect of hydrogen on the low-frequency EIS impedance results. (C) 2011 Elsevier Ltd. All rights reserved.