Working reports

Posiva's working reports are used to publish research results related to the practical aspects of the final disposal of spent nuclear fuel. Approximately one hundred working reports are published every year, usually in Finnish or English. The reports are written by Posiva employees or specialists from third party organisations. The working reports are an important tool for distributing the results of research work. All working reports are published on the Posiva website.

Workreport 2009-115



Assessment of Backfill Design for KBS-3V Repository


Keto, P., Dixon, D., Jonsson, E., Börgesson, L., Hansen, J. & Gunnarsson, D.



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Posiva and SKB initiated a joint programme BACLO (Backfilling and Closure of the Deep repository) in 2003 with the aim to develop methods and materials for backfilling of deposition tunnels. This report summarises the work done in the third and final phase of the BACLO programme. The main objective of this phase was to study how the various processes active during backfill installation and saturation as well as technical constraints affect its design basis. The work focused on the performance and technical feasibility of a block backfill concept, which calls for filling the majority of the tunnel volume with pre-compacted backfill blocks and the remaining volume with bentonite pellets.

Several backfill composition alternatives were chosen for study and they consisted of clay materials with differing amounts of swelling minerals. A large body of information was gained on the effect of different processes on the performance of these backfill options, e.g. water inflow, piping, erosion, self-healing, homogenisation and interaction between backfill and buffer in various laboratory and small-scale field tests. More practical tests included e.g. studies how the blocks and pellets could be installed to the deposition tunnel.

Based on the new information on the effect of the processes investigated and the estimated achievable block filling degree and backfill density, recommendations were made concerning material selection, backfill layout and technical issues. In addition, issues requiring further attention to verify the long-term performance of the proposed backfill concept are identified and listed.


BACLO, block backfill, performance, processes, technical feasibility


Assessment of Backfill Design for KBS-3V Repository. Working Report 2009-115 (pdf) (5 MB)


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