Concept and design of engineered barriers in Swiss repository projects

The system of engineered safety barriers envisaged in Switzerland for high-level and intermediate/low-level waste repositories are described and discussed. For high-level waste repositories in the granitic bedrock of northern Switzerland, the system of engineered barriers would consist of the waste matrix itself (vitrified waste from the reprocessing plant), a thick-walled overpack made of cast steel and designed to have a minimum life expectancy of 1000 years in the repository environment and finally a backfill made of highly compacted bentonite clay. In the case of the intermediate/low-level waste repositories, the engineered barriers system will in all cases comprise the cement and/or bitumen waste matrix (from the waste immobilization plant) and a backfill (probably, but not necessarily on a cementitious basis) with a sufficient porosity and hence gas conductivity (gas being generated by the anaerobic corrosion of steel in the repository). Depending on the hydraulic properties of the host rock an engineered hydraulic barrier may also have to be envisaged. (orig.)