GRS is investigating sealing and backfilling materials planned to be utilized in a nuclear repository in a salt formation. The program aims at providing experimental data needed for the theoretical analysis of the long-term sealing capacity of the seal system, including performance of the excavation damaged zone (EDZ). Experimental investigations on the long-term recompaction behavior of damaged rock salt itself and in interaction with the sealing system, under partial or near-full brine saturation, are performed. Rock salt samples for the experiments are taken from the vicinity of an existing dam that has been loaded in situ by the creeping rock salt for more than 10 years. The interaction with sealing materials is simulated by using hollow cylinders of salt equipped with a central concrete seal in isostatic cells. The focus of the work is on a systematic investigation of the material behavior leading to EDZ recompaction. It should result in a set of material parameters needed to treat the process in a numerical way.
On behalf of the German ministry for economics and energy (Bundesministerium fuer Wirtschaft und Energie, BMWi), GRS performs application-oriented safety research related to radioactive waste management in Germany. Among others, GRS is investigating sealing and backfilling materials planned to be utilized in a repository in a salt formation.
The German safety requirements for a repository of heatgenerating nuclear waste  comprise several safety principles, the most important ones being:
• Radionuclides and other contaminants in the waste must be concentrated and contained in a containment-providing rock zone (CRZ) and thus be isolated from the biosphere as long as possible.
• Waste disposal must ensure that release of radionuclides from the repository enhances only insignificantly the risks resulting from natural radiation exposure.
A robust barrier system is required to ensure that the safety principles are met.