Workreport 2007-29



Far-Field Thermal-Mechanical Response of One- and Two-Storey Repositories in Olkiluoto


Ikonen, K.



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This report contains results from far-field temperature and deformation analysis of the spent nuclear fuel repository in Olkiluoto. The objective of the analyses was to determine dimensions of the tensile stressed bedrock above the repository near the ground surface. Tensile stresses may open fractures in rock mass and ground water flow may become faster, if suitable pressure differences exist and further, potential for radio-nuclide transport from leaking canisters becomes higher to upward direction, towards biosphere. In considering stress state far from the rectangular repository the most essential parameters are the length, width and depth of the repository and the total decay heat density. Other details, like vertical or horizontal orientation of canisters is of less importance when considering situation far from the repository. The absolute value of the stress locally in the bedrock depends remarkably on the existing compressive natural in-situ stresses, which have different values in various orientations. The estimated Olkiluoto in-situ stresses based on the site characterization investigations have been taken into account.

The depth in tensioned volume extends in the one-storey repository to the depth of 94…107 m after about 300 years and in the two-storey repository to the depth of 129…146 m. The maximum tensile strain on the ground surface is about 0.00024 after about 600 years. Two-dimensional plane strain analyses gave conservative results when compared with more realistic three-dimensional analyses. When assuming the decreased deformation modulus for the rock mass due to the tensile cracking very conservatively the maximum depth of the tensile stressed rock is increased at most 10%. Ground uplift reaches its maximum of 6.9 cm about 1 230 years in the one-storey repository and 12.6 cm in the two-storey repository after about 1 400 years.


TM analyses, far-field stresses in repository for spent nuclear fuel, repository, Olkiluoto, decay heat


Far-Field Thermal-Mechanical Response of One- and Two-Storey Repositories in Olkiluoto (pdf) (647.7 KB)


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