The present paper investigates the effect of chloride and sulfate additions on corrosion of low-alloyed steel in a cladding flaw of a nuclear reactor pressure vessel using in-situ electrochemical impedance spectroscopy coupled to ex-situ characterization of the oxides by surface analytical techniques. Impedance data are interpreted by the mixed-conduction model for oxide films to yield estimates for the main kinetic and transport parameters of the corrosion process. It can be concluded that the effect of chloride/sulfate transients on low-alloyed steel oxides is moderate, concerns mostly the processes at the inner layer/coolant interface and is to a certain extent reversible. (C)2015 Elsevier Ltd. All rights reserved.