// Repository Design, Closure of Underground Cavities

ELSA

Shaft closures for repositories of high-level radioactive waste

The planned and implemented shaft closures in salt formations since 1994 were evaluated regarding their transferability to a repository for high-level radioactive waste (HAW). Furthermore, international activities related to the development and design of shaft closures were researched, and their technical status and potential transferability for a HAW repository in Germany were assessed. The methodology for applying the proof concept of partial safety factors was outlined. The application of the concept to a geotechnical closure structure is fundamentally feasible. Two individual proofs were conducted using the example chosen shaft closure concept of the preliminary safety analysis for Gorleben (VSG) to explain the methodology. This introduction facilitates later proof based on recognized procedures for the planned large-scale experiments. Site-specific boundary conditions are the basis for proof and design of the sealing system. These were compiled and explained according to current knowledge. General and specific requirements for the design of shaft closure structures, particularly at salt and claystone sites, were described. The requirements are mainly derived from overarching safety requirements (BMU 2010) and the requirements according to existing safety and proof concepts from the projects ISIBEL, VSG, and ANSICHT. All requirements were summarized in an overview. Finally, existing knowledge deficits were identified.