Metal-matrix corrosion studies in Canadian shield granitic groundwaters

The Canadian Nuclear Fuel Waste Management program is evaluating two basic supported-shell container concepts for used-fuel immobilization. One concept uses a compacted particulate material within the container to support a thin, corrosion-resistant shell. The other concept, called the metal-matrix concept, uses a cast-in-place metal matrix for shell support. This paper describes corrosion studies on the candidate matrix materials, lead, zinc and aluminum-7 wt.% Si (Al-7 wt.% Si), in the temperature range 293 to 423 K and the dissolved oxygen content range 8 to 410 mg/L. Test specimens were analyzed for general and localized corrosion and the corrosion products were identified. The results showed that, unlike lead, zinc and Al-7 wt.% Si are susceptible to localized corrosion. Lead showed only low general corrosion rates of 2 to 83 μm/a compared with zinc (36 to 15,800 μm/a) and Al-7 wt.% Si (6 to 209 μm/a) in the above temperature and oxygen content ranges. Maximum pit depths of about 0.9 mm on Al-7 wt.% Si and 0.6 mm on zinc were observed. These results indicate that, of the candidate matrix metals studied, lead has the greatest potential to retard radionuclide release from used-fuel disposal containers. 10 references, 7 figures, 2 tables