5. Oxidation – Corrosion

Zirconium alloys and hafnium resist well in water and steam under nuclear reactor operating conditions, at around 300°C. The oxide layers formed reach a few tens of microns, rarely more than 100 µm, after 3 to 6 years (under neutron irradiation).

• In air, oxidation is highly temperature-dependent, as shown in table 3 . The oxide layer is protective at low thicknesses (typically 3-10 µm), but degrades beyond that. For this reason, zirconium can be used at low temperatures (below 400 or 500°C), but oxidizes rapidly at higher temperatures. Nitriding only takes place above 800°C, when oxygen pressure is low.