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Evaluation of Repository Concepts for the Disposal of Spent Fuel on the Basis of Geotechnical Safety Indicators and Exploration Data

Michael Langer, Manfred Wallner

Nuclear Technology

Volume 121 / Number 2 / February 1998 / Pages 199-211


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Site-specific data of the Gorleben salt dome (e.g., the geological structure of the salt dome and the geomechanical properties of the evaporite) are presented in the form of a working model to optimize the various repository concepts discussed within the German research project "Direct Disposal of Spent Fuel" and to compare their long-term effects.

A comparative evaluation of the different emplacement concepts was made on the basis of the following calculated results, which are considered decisive: temperatures in the repository, temperatures in the salt dome/overburden transition zone, tensile stresses at the top of the salt dome zone, and uplift at the ground surface.

The thermal and thermomechanical consequences of four preselected emplacement concepts do not differ very much. The rock mechanical analyses of the far field do not indicate any particular concept as being clearly preferable.

The following results of the parameter variations (creep capacity and width of the repository field) are significant. A reduction in the repository field width gives lower maximum temperatures for the same specific heat load. An evaporite formation with a high creep capacity leads to significantly lower stress reduction at the top of the salt dome; tensile stresses do not occur. The stress reductions at the top of the salt dome are also less, but the horizontal stress orthogonal to the repository still lies in the tensile zone, if a low creep capacity of the rock salt is assumed.

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