Radiation enhanced degradation of aluminium mirrors for remote handling and diagnostics applications: Effect of humidity

High quality mirrors will be required for different diagnostic and remote handling systems in International Thermonuclear Experimental Reactor (ITER). The possibility of radiation enhanced surface degradation has been assessed. Unprotected Duralumin discs and high quality SiO overcoated aluminium on Pyrex mirrors have been irradiated with 60Co gamma rays at 12 Gy/s up to 50 MGy. Irradiations from 303 to 523 K have been performed in air and nitrogen. It has been observed that humidity is a key factor in the degradation process and produces severe corrosion on the aluminium mirror surface even with SiO overcoating. SEM and XPS analysis of chemical species formed on the surface indicate that the degradation produces aluminium hydroxide compounds, and the corrosion corresponds to a filiform mechanism.