The influence of groundwater anions on the impedance behaviour of carbon steel corroding under anoxic conditions

The anoxic corrosion of carbon steel liners to produce Fe2+ and H-2 within copper nuclear waste containers could lead to the scavenging of the radiolytic oxidants (H2O2, O-2) required to drive nuclear fuel (UO2) corrosion and the release of radionuclides. Steel corrosion has been studied in solutions containing various concentrations of Na2CO3/NaHCO3, Na2SO4 and NaCl to simulate an anticipated change in environment from carbonate-dominated to chloride-dominated groundwater composition over time. A combination of electrochemical techniques, scanning electron microscopy, and in situ Raman spectroscopy has been used. In concentrated carbonate solutions, corrosion is maintained within pores in a siderite ((FeCO3H2O)-H-.) deposit by the complexation of Fe2+ by HC03- and the reduction of protons supplied by HC03- dissociation. In mixed-anion solutions at lower CO32-/HCO3- concentrations, a compact green rust deposit covers the surface and the corrosion rate is suppressed. In concentrated NaCl solutions, the absence of CO32-/HCO3- buffering leads to a rapid shutdown of the corrosion process which may be aided by the formation of Fe-III. surface phases if traces of dissolved 0, are available. (c) 2005 Elsevier Ltd. All rights reserved.