Workreport 2007-35



Assessment of Potential Perturbations to Posiva’s SF Repository at Olkiluoto from the ONKALO Facility


Alexander, W. R. & Neall, F. B.



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Although the site of the proposed spent fuel repository at Olkiluoto in southwest Finland has been extensively investigated over the last fifteen years, Posiva decided to construct a rock characterisation facility (RCF) at the site to collect more detailed information on the host rock. The data provided by the ONKALO RCF will support the detailed repository design and safety assessment (SA) and will allow construction and disposal methods to be tested under relevant in situ conditions. ONKALO has been so designed that it can act as access routes and auxiliary rooms for the SF repository and so may be in use for the entire operational phase of the repository (currently up to 100 years).

Extensive experience from deep mining suggests that such an extended period of operation could have a major impact on both the host rock formation and any nearby facilities, such as the SF repository, and, consequently, Posiva decided to investigate potential perturbations to the repository caused by the existence of ONKALO. A preliminary assessment was carried out in 2003, before construction of the RCF began, and this was recently partially updated in early 2006. This current report represents the most recent update of these reports and has the primary aims of:

  • checking if the previous reports have missed any essential issues
  • evaluating whether the identified issues have been treated in an appropriate manner
  • updating the reports in the light of new information
This is carried out based on data from ONKALO itself and on improved understanding of some of the perturbation mechanisms identified in the original studies along with a consideration of newly identified processes. This report differs from the previous studies in addressing the issues in a more SA-oriented manner (for example, focussing the examination of potential perturbations on a re-worked FEP list), allowing the work reported here to be more easily dovetailed with future SA studies on the Olkiluoto repository. Although outwith the remit of this report, operational safety is also considered due to the potential of accidents and incidents to significantly disrupt the programme.

Note that the impacts of constructing the SF repository on the Olkiluoto area are covered elsewhere and neither this nor the repository SA will be addressed here. Rather, the focus of this report is on ONKALO-specific issues that could impact the performance of the Olkiluoto SF repository. Where possible, potentially detrimental phenomena are identified and methods to avoid such issues proposed. Lastly, due to the fact that construction of the ONKALO facility is still ongoing, there remain many uncertainties regarding the impact on the site, so the assessment of any perturbations considered here are generally on the conservative side so that worse-case scenarios for Olkiluoto can be obtained.


ONKALO, perturbations, geochemical, OPC, low alkali cement, FEPs, foreign materials


Assessment of Potential Perturbations to Posiva’s SF Repository at Olkiluoto from the ONKALO Facility (pdf) (2.2 MB)


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