Technischer Bericht NTB 82-08

During final storage of radioactive waste the corrosion behaviour of the canister materials is an important parameter. In this study the external corrosion behaviour of unalloyed steel, cast steel and cast iron in water-bearing granite rocks is discussed with a particular view to the conditions in Switzerland (temperature, pressure, water composition, etc.). The report is based on a critical literature review, on the authors' own experience and on experience from other fields of technology. Furthermore, model calculations are made for corrosion rates to be expected in the presence of a mass transfer barrier.

The most important results are as follows:

• corrosion rates in waters and soils are low, provided oxygen is excluded or protective layers are formed,
• under the expected conditions all of the relevant waters can produce significant corrosion
• the pressure dependence of the corrosion rate is small, while the temperature dependence is large,
• in the presence of an effective convection and diffusion barrier (Bentonite) the corrosion rate is very small (10^-5 mm/year),
• if such a barrier maintains its properties for the required lifetime of the final storage system the corrosion rate of the canister material can be neglected.