Systematic investigation on the corrosion of iron under conditions relevant to Storage of nuclear waste

Corrosion tests were performed on steel samples in q‐brine (pH 4.9), and for comparison in phthalate buffer (pH 4.9) and borate buffer (pH 8.4) at 170°C for 30 h in an autoclave. The samples were subsequently investigated by a wide variety of electrochemical, optical and UHV methods. A systematical combination of both non‐modifying and modifying methods was employed to allow for all measurements to be performed on a small number of samples. In borate buffer (pH 8.4), a thick (200 nm), homogeneous passivating oxide layer is found to build up on iron under test conditions (170°C, 30 h), resembling the anodic oxide layer (+ 1 V, 25°C) with respect to its optical and n‐semiconducting properties. No evidence for a barrier‐type layer is found for samples treated in phthalate buffer (pH 4.9) at 170°C for 30 h. The iron surface is covered by a precipitate layer in this case. In the chloridic q‐brine, a precipitate layer of Mg‐Fe‐oxichlorides is formed and large‐scale active corrosion is observed.