POST CLOSURE SAFETY OF THE MORSLEBEN REPOSITORY

After the completion of detailed studies of the suitability the twin-mine Bartensleben-Marie, situated in the Federal State of Saxony-Anhalt (Germany), was chosen in 1970 for the disposal of low and medium level radioactive waste. The waste emplacement started in 1978 in rock cavities at the mine’s fourth level, some 500 m below the surface. Until the end of the operational phase in 1998 in total about 36,800 m³ of radioactive waste was disposed of. The Morsleben LLW/ILW repository (ERAM) is now under licensing for closure. After completing the licensing procedure the repository will be sealed and backfilled to exclude any undue future impact onto man or the environment. The main safety objective is to protect the biosphere from the harmful effects of the disposed radionuclides. Furthermore, classical or conventional requirements call for ruling out or minimizing other unfavourable environmental effects. The ERAM is an abandoned rock salt and potash mine. As a consequence it has a big void volume, however small parts of the cavities are backfilled with crushed salt rocks. Other goals of the closure concept are therefore a long-term stabilization of the cavities to prevent a dipping or buckling of the ground surface. In addition, groundwater protection shall be assured. For the sealing of the repository a closure concept was developed to ensure compliance with the safety protection objectives. The concept anticipates the backfilling of the cavities with hydraulically setting backfill materials (salt concretes). The reduction of the remaining void volume in the mine causes in the case of brine intrusions a limitation of the leaching processes of the exposed potash seams. However, during the setting process the hydration heat of the concrete will lead to an increase of the temperature and hence to thermally induced stresses of the concrete and the surrounding rocks. Therefore, the influence of these stresses and deformations on the stability of the salt body and the integrity of the geological barrier was examined by 2D and 3D thermo-mechanical computations. The compliance of the safety objectives are proved on the basis of safety evidence criteria. It can be concluded that the closure concept is able to serve all conventional and radiological safety objectives.