The engineering geological and rock mechanics activities for radioactive waste repositories are strongly linked to the safety concepts for the repository projects. Key issues are: proper site characterisation, proof of geotechnical safety and quantitative description of geomechanical processes and of geological scenarios for long-term safety assessment calculations. A status report of the German repository projects Gorleben and Konrad based on this concept will be presented. While these projects are still being pursued the former Morsleben salt mine in Sachsen-Anhalt, which was used as a repository for short-lived low and intermediate level waste from 1981 until 1991 has resumed its operation in 1994. In the paper some issues are demonstrated by an example: site characterisation work for a salt dome, geotechnical measurements and calculations to proof the stability of a mine, and considerations of geomechanical natural analoga for calibration of constitutive laws. For the future the role and contributions of geoscientific and rock mechanics work within the safety assessment issues (e.g. geomechanical safety indicators) must be identified in greater detail.
Since the early sixties, the radioactive waste disposal policy in the Federal Republic of Germany has been based on the decision that all kinds of radioactive waste are to be disposed of in deep geological formations. The basic aspects which must be taken into account to achieve this objective of disposal are compiled in the „RSK-Sieherheitskriterien für die Endlagerung radioaktiver Abfälle" (Safety Criteria for the Disposal of Radioactive Waste in a Mine). The following criteria are considered to be the most important ones: The required safety of a repository constructed in a geological formation must be demonstrated by a site- specific safety assessment which includes the respective geological situation, the technical concept of the repository including its scheduled mode of operation, and the waste packages intended to be disposed of. In the post-closure phase, the radionuclides which might reach the biosphere via the water path as a result of transport processes not completely excludable must not lead to individual dose rates which exceed the limiting values specified in section 45 of the German Radiation Protection Ordinance (0.3 mSv/a concept).
Natural geological and geotechnical barriers are an important part of a multiple-barrier system. Thus, the loadbearing capacity of the rock (expressed, for example, through subsidence or cavern stability), its geological and tectonic stability (e.g. mass movement or earthquakes), and its geochemical and hydrogeological development (e.g. groundwater movement and the potential for dissolution of the rock) are important aspects of the safety analysis. Therefore safety cannot be assessed from a purely engineering point of view, but must include geological factors. A site-specific modelling of geotechnical and geomechanical features and processes is needed.
The site specific geotechnical safety plan has to include the individual dose/risk scenarios and possible contingencies for which again measures and/or verifications are required. The safety plan has to be updated as new experience become available (e.g. during the construction or during the operation of the plant).