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<p>The Federal Company for Radioactive Waste Disposal (BGE mbH) is responsible for the execution of the German site selection procedure for high-level radioactive waste. The aim is to identify a repository site that ensures the best possible safety for the disposal of high-level radioactive waste for at least one million years. Three potential host rocks are considered for disposal in Germany: rock salt, claystone and crystalline rock. The German site selection procedure consists of three consecutive phases with a continuously increasing level of detail. The first step of phase I served to determine sub-areas based on different geoscientific criteria. In this process 90 suitable areas were identified. The second step of phase I comprises representative preliminary safety assessments to further narrow down the sub-areas (see Figure 1).</p> <p><img src="" alt="" /></p> <p>Figure 1: German Site Selection Procedure</p> <p>For these assessments, a preliminary concept and dimensioning of the deep geological repository is required, among other aspects. The primary input data for the preliminary design of the repository are the respective host rock properties, the inventory data of the high-level radioactive waste as well as a preliminary safety concept for the disposal system. Since there are only limited area-specific data available as no exploration is part of this early stage of the selection procedure, a two-stage method has been developed for the determination of the required area of the potential repository, consisting of a host rock specific and a site specific part. The objective of the first, host rock specific stage is to perform an analysis irrespective of the prevailing geological conditions at the considered locations. The aim is to obtain the areal extend of a potential repository as a function of the depth, the initial temperature in the host rock and mechanical properties of the host rock. Another important topic is the assessment of favorable depth ranges of the repository. Within the second stage, the function is used with available site-specific data to obtain the possible size of the repository at this specific site.</p> <p>This contribution will provide an overview of the first stage within the aforementioned methodology for the development of the preliminary design of the repository as part of the representative preliminary safety assessments. </p>

We propose a frictionless contact formulation for isogeometric analysis, which combines a collocated formulation for the contact surfaces with a standard Galerkin treatment of the bulk. We denote it as isogeometric Collocated Contact Surface (CCS) formulation. The approach is based on a simple pointwise enforcement of the contact constraints, performed in this study with the penalty method. Unlike pointwise (node-to-surface or point-to-surface) contact algorithms in the Galerkin framework, the CCS formulation passes the contact patch test to machine precision by naturally exploiting the favorable properties of isogeometric collocation. Compared with approaches where the discretization of both bulk and contact surfaces is based on collocation, the CCS approach does not need enhancements to remove oscillations for highly non-uniform meshes. With respect to integral contact approaches, the CCS algorithm is less expensive, easier to code and can be added to a pre-existing isogeometric analysis code with minimal effort. Numerical examples in both small and large deformations are investigated to compare the CCS approach with some available contact formulations and to demonstrate its accuracy.