Geoscientific investigations at the Gorleben salt dome have been conducted to prove its suitability as a repository for high-level radioactive waste. Part of the investigation is the geotechnical safety analysis to assess the integrity of the geological barrier under thermal loading caused by heat-generating wastes. To this end, the geological structure of the rock, as well as appropriate constitutive material models must be taken into account to analyse the long-term deformation and dilatancy of the rock salt. The paper describes two numerical 3-D models of the emplacement of wastes. The first model deals with the emplacement in drifts located at the 860-m level. The second model considers the borehole disposal concept involving the emplacement of waste canisters in vertical boreholes. The calculations were performed for a time period of 10,000 years. The calculated stresses are used to evaluate the integrity of the salt barrier. For this purpose, the dilatancy criterion and the hydraulic criterion are considered.
Geoscientific surface exploration looking at the suitability of the Gorleben salt dome as a potential site for a geologic repository for high radioactive heat-generating waste began in 1977. This work was followed up by underground exploration of the site beginning in 1983. The explorationwas interrupted for ten years from 2000 to 2010 as part of a moratorium and was continued in November 2010.
The Federal Office for Radiation Protection (BfS) is responsible for the planning, construction, and operation of the Gorleben site. The Federal Institute for Geosciences and Natural Resources (BGR) deals with the primary geoscientific questions, e.g. geology, geophysics, geotechnics, and modelling. In parallel to the continuation of the investigation activities, the Federal Ministry of the Environment, Nature Conservation and Nuclear Safety (BMU) initiated the project "Preliminary Safety Analysis of the Gorleben Site (VSG)" to assess the safety of the Gorleben salt dome on the basis of current knowledge.
In the past, model calculations have been undertaken by BGR to analyse the mechanical behaviour of mine components like shafts and drifts. Thermally induced stresses and strains have been predicted on a large scale. These stresses and strains will be caused over large time periods by the disposal of heatgenerating high-level waste and are basic parameters for evaluating the long-term mechanical integrity of the salt barrier.
The paper describes two different numerical 3-D models of the Gorleben salt dome which have been used for different kinds of waste emplacement to analyse the far-field integrity of the salt barrier. Both models describe a characteristic geological cross section of the salt dome considering the main geological layers of the salt structure and the overburden in a detailed way. The first model deals with the emplacement of Pollux casks in drifts located at the 860-m level. The second model considers the borehole disposal concept involving the emplacement of BSK3 fuel element canisters in vertical boreholes at a depth of 870 to 1170 m.
The model calculations have been carried out using the special purpose JIFE code (Faust et al. 2011).