The radioactivity in the primary circuit of pressurized water reactors (PWR) mainly comes from the activation of corrosion products in the core of PWR; corrosion products dissolve from the oxide scales developed on steam generator tubes of alloy 690. The controlling of this process, oxidation and dissolution, requires a detailed knowledge of the microstructure and chemical composition of oxide scales. Alloy 690 was studied as tubes and plates with three various surface states (as-received, cold-worked, electropolished). Corrosion tests were performed at 325°C and 120 or 155 bar in primary water conditions (B/Li(1000/2 ppm, [H2] = 30 cm3 kg−1 TPN, [O2]<5 ppb); test durations ranged between 24 and 2160 hours. Corrosion tests were carried out in a static autoclave made of stainless steel, and in one recirculating autoclave made of titanium alloy (TITANE recirculating autoclave). Characterisation of the oxide scales grown in representative conditions of the primary circuit was performed by several techniques (SEM, (X)TEM, SIMS, XPS, GIXRD, RBS). These analyses revealed the essential role of the finegrained cold-worked superficial zone of perturbed microstructure presents on as-received and coldworked specimens. They also gave some insights on the growth mechanisms of corrosion products scales.