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Archaeological analogs for verification of container lifetime models for deep radioactive waste repositories : Final report of project TK01010040
Stoulil, J. ; Mukhtar, S. ; Lhotka, M. ; Bureš, R. ; Kašpar, V. ; Šachlová, Š. ; Pecková, A. ; Havlová, V. ; Danielisová, Alžběta ; Malyková, Drahomíra ; Barčáková, Ludmila ; Machová, Barbora ; Březinová, Helena ; Ottenwelter, Estelle ; Němeček, J. ; Němeček, J.
More than 200 artefacts from 15 localities were studied within the scope of this project. 4 localities were crucial, because those were pond beds with continual flooding. Soils at all localities were coarser compared to bentonites and lacked swelling ability. Pore solutions of the soils were very similar to bentonite pore solutions. They differ in cation composition, but anion composition was similar, which is more important for corrosion behaviour. The environment was not completely anaerobic, what influenced the composition of corrosion products. The compounds were oxides and oxohydroxides. Very low oxidation-reduction potential (fully anaerobic environment) is necessary for the formation of carbonate-based corrosion products, that were detected as major corrosion products in the previous lab and in situ experiments on another projects. Nevertheless, the oxygen transport was very slow and the contribution of aerobic corrosion was negligible compared to anaerobic corrosion. The evaluation of archaeological artefacts revealed very important factors influencing corrosion mechanism in latter stage of soil burial. Precipitation of corrosion products is a driving phenomenon for transport limitation and decrease of corrosion rate in the early stage of burial, while the ferrous species transport is limited extensively within the latter stage resulting in mechanical stress of inner corrosion products layers to previously formed corrosion products and subsequent cracking. This mechanical damage is repeated in the cycle. The mechanical properties of corrosion products are poor, they are easily deformable and very porous. The project has revealed a very important phenomenon, necessary for the right lifetime estimation, which would not be obvious based on the short-term experiments data.
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