Impact of iron-reducing bacteria on the corrosion rate of carbon steel under simulated geological disposal conditions.

The current projects for the disposal of high-level radioactive waste rely on underground burial and confinement by metallic envelopes that are susceptible to corrosion processes. The impact of microbial activity must be fully clarified in order to provide biological parameters for predictive reactive transport models. This study investigates the impact of hydrogenotrophic iron-reducing bacteria (Shewanella oneidensis strain MR-1) on the corrosion rate of carbon steel under simulated geological disposal conditions by using a geochemical approach. It was found that corrosion damage changes mostly according to the experimental solution (i.e., chemical composition). Magnetite and vivianite were identified as the main corrosion products. In the presence of bacteria, the corrosion rate increased by a factor of 1.3 (according to weight loss analysis) to 1.8 (according to H2 measurements), and the detected amount of magnetite diminished. The mechanism likely to enhance corrosion is the destabilization and dissolution of the passivating magnetite layer by reduction of structural Fe(III) coupled to H2 oxidation.

Combined geochemical and electrochemical methodology to quantify corrosion of carbon steel by bacterial activity.

The availability of respiratory substrates, such as H2 and Fe(II,III) solid corrosion products within nuclear waste repository, will sustain the activities of hydrogen-oxidizing bacteria (HOB) and iron-reducing bacteria (IRB). This may have a direct effect on the rate of carbon steel corrosion. This study investigates the effects of Shewanella oneidensis (an HOB and IRB model organism) on the corrosion rate by looking at carbon steel dissolution in the presence of H2 as the sole electron donor. Bacterial effect is evaluated by means of geochemical and electrochemical techniques. Both showed that the corrosion rate is enhanced by a factor of 2-3 in the presence of bacteria. The geochemical experiments indicated that the composition and crystallinity of the solid corrosion products (magnetite and vivianite) are modified by bacteria. Moreover, the electrochemical experiments evidenced that the bacterial activity can be stimulated when H2 is generated in a small confinement volume. In this case, a higher corrosion rate and mineralization (vivianite) on the carbon steel surface were observed. The results suggest that the mechanism likely to influence the corrosion rate is the bioreduction of Fe(III) from magnetite coupled to the H2 oxidation.

Influence of hydrogen-oxidizing bacteria on the corrosion of low carbon steel: Local electrochemical investigations.

Low carbon steel has been considered a suitable material for component of the multi-barrier system employed on the geological disposal of high-level radioactive waste (HLW). A non negligible amount of dihydrogen (H2) is expected to be produced over the years within the geological repository due to the anoxic corrosion of metallic materials and also to the water radiolysis. The influence of the activity of hydrogen-oxidizing bacteria (HOB) and iron-reducing bacteria (IRB) on carbon steel corrosion is considered in this study because of the high availability of energetic nutriments (H2, iron oxides and hydroxides) produced in anoxic disposal conditions. Local electrochemical techniques were used for investigating the activity of IRB as a promoter of local corrosion in the presence of H2 as electron donor. A local consumption of H2 by the bacteria has been evidenced and impedance measurements indicate the formation of a thick layer of corrosion products.