Lessons from nature : the behaviour of technical and natural barriers in the geological disposal of spent nuclear fuel

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Acta polytechnica Scandinavica. Ci, Civil engineering and building construction series, 124
This work deals with the study of the long-term performance of materials and elements involved in the near- and far-field of an underground nuclear waste repository. Materials and elements occurring in nature are similar, or at least analogous, to the materials and elements manufactured or processed by man. Also, natural processes may be similar to those envisaged as occurring in a nuclear waste repository. This similarity makes it possible to study the behaviour of those materials in nature and to compare it with the behaviour of the manufactured materials to be used in a repository. As many materials and elements have been in the natural environment for long time periods (thousands to million of years), the data obtained can be extrapolated to estimate the future evolution of similar components in a nuclear waste repository. Thinking by analogy is the process of comparison, with those materials, elements and environments used to perform the studies that allow the comparison to be regarded as natural analogues. The Hyrkkölä U-Cu mineralisation (SW Finland) was studied as an analogue to the behaviour of copper canisters in crystalline bedrock. This analogue could also address the interaction between copper corrosion products and uranium. Copper sulphides are shown to retain up to 25% of uranium as U (IV) even if oxidizing conditions prevail. Furthermore, uranium was observed in smectite (main component of bentonite) associated with native copper and cuprite, which constitutes an analogue to the behaviour of the repository near-field materials in a natural oxidizing environment. In addition to the Hyrkkölä analogue, the issue of irreversible sorption or uranium immobilization is also addressed, in the studies of the boulder rock near Hämeenlinna. The behaviour of U, Th, and rare earth elements (REE) as analogues to the long-lived actinides is also evaluated in groundwater and rock samples at Olkiluoto (SW Finland). U and Th were shown to be released more easily from clean fracture surfaces than from fracture surfaces covered with calcite or kaolinite. From the studies presented here, it may be seen that the Hyrkkölä analogue has been applied so far in safety assessments, mainly to demonstrate the canister lifetime and to a lesser extent to confirm the interactions between copper corrosion products and uranium. Up to the present, the issues of irreversible sorption or immobilization and the analogy between REE and actinides have not been taken into account in safety assessments. The results of the studies presented here indicate strong prospects that these issues could be new and powerful tools indispensable to safety assessments. More research and understanding is required, however, to form them into operational tools for this application.
geological disposal, natural analogues, native copper, uranium, rare earth elements, spent fuel, Olkiluoto
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  • Marcos, N., 1997. The Hyrkkölä native copper mineralization: A natural analogue for copper canisters. Mat. Res. Soc. Symp. Proc. 465, 1153-1160. [article1.pdf] © 1997 Materials Research Society. By permission.
  • Marcos, N., Ahonen, L., Bros, R., Roos, P., Suksi, J. and Oversby, V., 1999. New data on the Hyrkkölä native copper mineralization: A natural analogue for the long-term corrosion of copper canisters. Mat. Res. Soc. Symp. Proc. 556, 825-832. [article2.pdf] © 1999 Materials Research Society. By permission.
  • Marcos, N., Suksi, J., Ervanne, H. and Rasilainen, K., 2000. Fracture smectite as a long-term sink for natural radionuclides - Indications from unusual U-series disequilibria. Radiochim. Acta 88, 763-766. [article3.pdf] © 2000 Oldenbourg Wissenschaftsverlag. By permission.
  • Marcos, N., Siitari-Kauppi, M., Suksi, J., Rasilainen, K., Finch, R.J. & Hellmuth, K-H., 2001. Discussion on the use of the matrix diffusion model after a multidisciplinary study of a granitic boulder sample. Mat. Res. Soc. Symp. Proc. 663, 1053-1063. [article4.pdf] © 2001 Materials Research Society. By permission.
  • Marcos, N., 2002. Low-temperature mobility of rare earth elements, U and Th at the Olkiluoto site, SW Finland. Mat. Res. Soc. Symp. Proc. 713, 825-832. [article5.pdf] © 2002 Materials Research Society. By permission.
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