Due to the reorientation of the search for a site for a final repository for heat-generating radioactive waste, which was initiated by the German Repository Site Selection Act as of July 23, 2013, all possible host rocks; i.e. salt, clay, and crystalline rock, become important. However, for an objective comparison of repository systems in different host rocks and an eventual assessment, adequate background knowledge is required.
Any safety and safety demonstration concept must be based on the Safety Requirements Governing the Final Disposal of Heat-Generating Radioactive Waste issued by the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety in 2010. These safety requirements comprise the so-called "CRZ concept" that stipulates that any applicant for a final repository for heat-generating radioactive waste needs to demonstrate that a containment providing rock zone (CRZ) is present that – together with the technical barriers – ensures the safe containment of the radioactive waste. The containment capacity of the CRZ (integrity) must be guaranteed for the reference period of one million years.
In summer 2015 the Project Management Agency Karlsruhe on behalf of the Federal Ministry for Economic Affairs and Energy contracted DBE Technology GmbH, BGR and GRS with the R&D project CHRISTA to start the development of a safety and safety demonstration concept for a HAW repository in German crystalline rock. One characteristic of crystalline rock is the presence of fractures. Thus, if this rock type is considered as host rock, one has to be aware that the integrity as such may be impaired from the outset. If and to what extent the "CRZ concept" can be applied to this type of rock and how the integrity requirement has to be defined in this case, is to be determined within the scope of this project. Regarding the integrity analysis, the basic question will be discussed, how important integrity can be for the description of the barrier function of a host rock that may contain fractures. What are the criteria that can be derived for the assessment of the integrity? The involvement of DBE TECHNOLOGY GmbH and its partners in tests in the URL Äspö in Sweden and the long-term experience gained in the German-Russian cooperation with regard to the site exploration and repository design in crystalline rock in the Russian Federation are a sound basis for this purpose. (M.J.)