Structural studies in connection with the construction of deep repositories for the storage of high-grade nuclear waste
Structural and fluid analysis can greatly assist studies aimed at the detailed characterization of potential sites for the construction of underground repositories for high-grade spent nuclear fuel. We have engaged with several studies in collaboration with SKB and Posiva OY, the companies responsible for the safe storage of nuclear waste in Sweden and Finland, respectively. The work undertaken consists in the study of brittle and ductile structures (i.e. brittle deformation zones, faults, fractures and associated fault rocks and shear zones) with the aim to document their character and kinematics as an input to an evaluation of the ductile and brittle deformational history of the regions under investigation. The results are used in the development of the conceptual models to use as input for the design of the repository layout in the target rock volumes. The data are also used to compute paleostress tensors and therefore to frame individual deformation events into a consistent sub-regional brittle deformation scheme. When present, fault rocks are studied to better constrain the deformation mechanisms that controlled the brittle structural evolution. Much attention is currently being paid at fluid-rock interaction mechanisms. Barbara Marchesini is a PhD student working on the role of the fluid phase during frictional-viscous cyclicity within brittle-ductile deformation zones in the seismogenic crust (project 2017-2019). The study is also in collaboration with the University of Plymouth.
International collaborations
Dr. Jussi Mattila – Posiva Oy Finland
Dr. Raymond Munier – SKB Sweden
Dr. Luca Menegon – Plymouth
Dr. Mark Anderson - Plymouth
Selected references
- Viola G. and Venvik Ganerød G. (2007): Oskarshamn site investigation: Structural analysis of brittle deformation zones in the Simpevarp-Laxemar area, Oskarshamn, southeast Sweden, Report from Phase 1. SKB P-07-41. Svensk Kärnbränslehantering AB. Available on line from www.skb.se.
- Viola G. and Venvik Ganerød G. (2007): Oskarshamn site investigation: Structural characterization of deformation zones (faults and ductile shear zones) from selected drill cores and outcrops from the Laxemar area – Results from Phase 2. SKB P-07-227. Svensk Kärnbränslehantering AB. Available on line from www.skb.se.
- Viola G. and Venvik Ganerød G. (2008): Oskarshamn site investigation: Structural characterization of deformation zones (faults and ductile shear zones) from selected drill cores from the Laxemar area – Results from Phase 3", Svensk Kärnbränslehantering AB. Available on line from www.skb.se.
- Viola G., 2008: Ductile and brittle deformation history of the Laxemar-Simpevarp area; an independent analysis based on local and regional constraints. SKB R-08-124. Svensk Kärnbränslehantering AB. Available on line from www.skb.se.
- Viola, G., Venvik Ganerød G. and Wahlgren, C.-H.( 2009): Unravelling 1.5 Gyr of brittle deformation history in the Laxemar-Simpevarp area, SE Sweden: a contribution to the Swedish site investigation study for the disposal of highly radioactive nuclear waste. Tectonics, 28, TC5007, doi:10.1029/2009TC002461.
- Saintot, A., Stephens, M.B., Viola, G. and Nordgulen, Ø. (2011): Brittle tectonic evolution and paleostress field reconstruction in the southwestern part of the Fennoscandian Shield, Forsmark, Sweden. Tectonics, 30, TC4002, doi:10.1029/2010TC002781.
- Viola, G., Mattila, J., Zwingmann, H. and Todd, A. (2011): Structural and K/Ar illite geochronological constraints on the brittle deformation history of the Olkiluoto region, southwest Finland" Posiva OY working report 2011-37.
- Viola, G., Zwingmann, H., Mattila, J. and Käpyaho, A. (2013): K/Ar illite age constraints on the Proterozoic formation and reactivation history of a brittle fault in Fennoscandia. Terra Nova, 25, 3, 236-244.
- Mattila, J. and Viola, G. (2014): New constraints on 1.7 Gyr of brittle tectonic evolution in southwestern Finland derived from a structural study at the site of a potential nuclear waste repository (Olkiluoto Island). Journal of Structural Geology, 67, 50-74.
- Marchesini, B., Garofalo, P.S., Menegon, L., Mattila, J. and Viola, G. (2019): Fluid-mediated, brittle-ductile deformation at seismogenic depth: Part I – Fluid record and deformation history of fault-veins in a nuclear waste repository (Olkiluoto Island, Finland). Solid Earth, 10, 809–838, doi: 10.5194/se-10-809-2019.
- Prando, F., Menegon, L., Anderson, M., Marchesini, B., Mattila, J. and Viola, G. (2020): Fluid-mediated, brittle-ductile deformation at seismogenic depth: Part II – Stress history and fluid pressure variations in a shear zone in a nuclear waste repository (Olkiluoto Island, Finland). Solid Earth, 11, 489–511, doi: 10.5194/se-11-489-2020.