In Germany it has been decided to analyse and compare different kinds of host rocks to identify an option for the disposal of high-level radioactive waste. As a starting point the "Kommission Lagerung hoch radioaktiver Abfallstoffe" (Commission for Disposal of Highly Radioactive Waste) has been implemented to develop criteria for identifying suitable sites as hosts for a repository for high-level radioactive waste. In December 2015 DBE TECHNOLOGY GmbH was commissioned by this commission to conduct an expert assessment and report specific to the "Areal Requirements of a Repository for Heat-Generating High-Level Radioactive waste". Based on the specific expertise and extensive studies that DBE TECHNOLOGY GmbH possesses through numerous R&D projects conducted on the design of repositories in the three host rocks (salt, clay and granite), mostly funded through the BMWi, it was possible to complete the assessment within the prescribed two month time frame.
Following the described scope of work, the repository areal requirements for three different host rock types in four variants were determined (salt: design temperatures 200 ° C and 100 ° C, clay: 100 ° C and granite: 100 ° C). The waste volume to be accounted for in the study was taken from the "National waste management program (NaPro)". Furthermore, following project specifications single-level drift disposal was considered for salt and clay rock types while vertical borehole disposal (KBS 3V concept) was considered for granite. Further constraints included the use of cylindrical, metallic modeled disposal container, uniform emplacement over a 30 year period and an adjustment of the container inventories to the respective design temperatures. To enhance comparability a consistent depth of 600 m for all repository variants was selected.
The expert assessment was conducted in multi-step process, including planning and supplementation of the design basis; defining material parameters for the host rock, containers, and backfill, as well as development of mathematical models, conduct of temperature calculations, conceptualization of repository layouts; and finally calculation of the areal extent of the repository in consideration of both subsurface disposal as well as operational support infrastructure needs.
The comparative assessment of the analytical results demonstrated that the smallest areal requirements were achieved for salt rock at a design temperature of 200°C. At similar design temperatures (i.e., 100°C) the total areal needs for the three considered variants were primarily determined by the differing thermal conductivity of the selected host rock and backfill material. For use in the site selection process the following calculated areal extents can be used as a planning basis: