Effect of radiolytic hydrogen peroxide in tritiated water on the first passivity of titanium

Titanium is an interesting metallic material for nuclear applications. This is due to its passivity ensured by a compact and chemically stable oxide film that spontaneously covers the metal surface. This work aims at studying the electrochemical behavior of titanium in the presence of tritiated water at pH 4 and containing hydrogen peroxide generated by radiolytic reaction. Tritium in tritiated water always causes difficulties in corrosion. The corrosion potential can be either in the active or prepassive regions depending on the concentration of radiolytic oxidizing species and intermediate species formed on the surface in the active region. Therefore, the behavior of titanium was studied by cyclic voltammetry and electrochemical noise in situ to provide an indication of mechanisms, transient formation and instabilities of oxide in active region. In the prepassivity and passivity, according to the results of electrochemical impedance spectroscopy and coulometric curves, titanium is protected by a semiconductor layer essentially formed of TiO2. Between the region of first and second passivity, oxide consists of a dielectric layer and a semiconductor layer. These two layers protect the titanium against corrosion.