Further Studies of the Anaerobic Corrosion of Steel in Bentonite
- PDF / 655,265 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 107 Downloads / 262 Views
Further Studies of the Anaerobic Corrosion of Steel in Bentonite Nick R. Smart1, Andrew P. Rance1, Liisa Carlson2, Lars O. Werme3 1 Serco Assurance, Culham Science Centre, Abingdon, Oxfordshire, OX14 3ED, U.K. 2 Geological Survey of Finland, P.O. Box 96, FIN-02151, Espoo, Finland. 3 SKB, Brahegatan 47, Box 5864 SE-102 40, Stockholm, Sweden. ABSTRACT In the horizontal emplacement concept (KBS-3H) for the disposal of radioactive waste, which is being developed in Sweden and Finland, copper canisters with cast iron inserts will be surrounded by bentonite buffer and mounted in perforated carbon steel support structures in boreholes within the bedrock. The groundwater will be reducing, leading to anaerobic corrosion of the ferrous material. It is important to understand both the effect of bentonite on the corrosion behaviour of the steel and the effect of the corrosion products on the performance of the bentonite. Previous work on the corrosion of steel in bentonite was extended to investigate a wider range of conditions, including the possible effects of alkaline plumes released from concrete support structures and the effect of chloride concentration and temperature on the corrosion rate of steel in bentonite. Corrosion rates were measured by collecting hydrogen produced by the anaerobic corrosion of iron. In addition, a range of analytical techniques was applied to study the composition and morphology of the corrosion products and the distribution and chemical state of the iron released into the bentonite. Comparison was also made between corrosion in compacted bentonite and artificial bentonite porewater. In the presence of bentonite, the corrosion product layer was relatively thin compared to fully aqueous conditions, probably because the ferrous ions released by corrosion exchanged with the bentonite interlayer or attached to the surface of the bentonite grains, rather than forming a separate iron oxide phase. INTRODUCTION In the horizontal emplacement concept (KBS-3H) for the disposal of radioactive waste, which is being developed in Sweden and Finland, copper canisters with cast iron inserts will be surrounded by bentonite buffer and mounted in perforated steel support structures in boreholes within the bedrock. The groundwater will be reducing, leading to anaerobic corrosion of the ferrous material, which will release hydrogen. It is important to understand both the effect of bentonite on the corrosion behaviour of the steel and the effect of the corrosion products on the characteristics of the bentonite. Previous studies have measured the corrosion rate and gas generation rate due to the anaerobic corrosion of steel in bentonite [1] and a limited amount of analysis was carried out on the composition of the bentonite surrounding the corroding iron. In the present paper further studies of the corrosion rate of steel in bentonite under a wider range of conditions are presented and more detailed chemical and physical analyses of the steel corrosion product and bentonite after the corrosion experiments are described
Data Loading...
