Shaft seals for HLW repositoriesPhilipp Herold1, Michael Jobmann1, Wolfram Kudla2, Matthias Gruner2

1DBE TECHNOLOGY GmbH, 2TU Bergakademie Freiberg7th US/German Workshop on

Salt Repository Research, Design and OperationWashington, DC

September 7-9, 2016

ABSTRACT

The R&D project "Shaft sealing systems for final repositories for high-level waste (ELSA) – Phase 2: Concept design for shaft seals and testing of functional elements of shaft seals", which is funded by the Federal Ministry for Economic Affairs and Energy (BMWi), was initiated to develop shaft sealing concepts for the two host rock options rock salt and claystone. These concepts are to be modular in design so that they can be adapted to suit the eventual site conditions. As no decision has yet been made on the choice of site for the final disposal of high-level waste and spent fuel, generic shaft sealing concepts have been developed based on currently existing host-rock data. Diversity and redundancy are basic design requirements for shaft sealing of repositories for high-level waste and spent fuel. Bitumen/asphalt will fulfill these basical requirements, in addition to clay-based sealing elements, such as binare mixtures of bentonite. Within the ELSA projcet, two already existing conceptual designs of bitumen/asphalt seals were tested in-situ and one new asphalt sealing system was developed and tested. All tests showed that sealing systems made of bitumen/asphalt lead to a permeability close to initial host rock permeability. Especially soft bitumen penetrates the EDZ and fills cracks, which was shown by a microstructure analysis of the removed bitumen seals. Additional, in-situ tests were realized for MgO-concrete and mixtures of crushed salt and clay. The in-situ tests of dynamic compaction of mixtures made of crushed salt and clay demonstrate the suitability of this technology for sealing construction. In a next step, the conventional equipment has to be modified for conditions inside a shaft. The use of MgO-concrete and mixtures of crushed salt and clay is limited to rock salt. Bimodal bentonite seals promissie functionally independent of the type of host rock. Sealing elements made of conventional binare bentonite mixtures and equipotential layers were tested in semi-scale tests, too.