A Study into the Localized Corrosion of Magnesium Alloy Magnox Al-80 Ronald N. Clark‡*, James Humpage**, Robert Burrows*, Hugh Godfrey***, Mustufa Sagir****, Geraint Williams** ‡Corresponding author. E-mail:
[email protected]. *National Nuclear Laboratory, Unit 102B, Sperry Way, National Nuclear Laboratory, Stonehouse, GL10 3UT, UK **Swansea University, Materials Research Centre, Bay Campus, Fabian Way, Crymlyn Burrows, Swansea, SA1 8EN, Wales, UK ***National Nuclear Laboratory, Workington Laboratory, Havelock Road, Derwent Howe, Workington, Cumbria, CA14 3YQ, UK ****Sellafield Limited, Hinton House, Birchwood Park Avenue, Risley, Warrington, Cheshire, WA3 6 GR, UK
[email protected] [email protected] [email protected] [email protected] [email protected] ABSTRACT Magnesium (Mg) non-oxidizing alloy, known as Magnox, was historically used as a fuel cladding material for the first-generation of carbon dioxide (CO2) gas-cooled nuclear reactors in the UK. Waste Magnox is currently stored in cooling ponds, pending final disposal. The corrosion resistance of Mg and its alloys is relatively poor, compared to modern cladding materials such as zirconium (Zr) alloys, so it is important to have a knowledge of the chloride concentration/pH dependence on breakdown and localized corrosion characteristics prior to waste retrievals taking place. Our results show that Magnox exhibits passivity in high pH solutions, with charge transfer resistance and passive film thicknesses showing an increase with immersion time. When chloride is added to the system the higher pH maintains Magnox passivity, as shown through a combination of potentiodynamic and time-lapse/post corrosion imaging experiments. Potentiodynamic polarization of Magnox reveals a -229 mV-decade linear dependence of breakdown potential with chloride ion concentration.