(GRS 493) Development of Chemical-hydraulic Models for the Prediction of Long-term Sealing Capacity of Concretebased Sealing Materials in Rock Salt

O. Czaikowski, U. Hertes, K. Jantschik, T. Meyer, H. C. Moog, B. Zehle

For the safe disposal of radioactive waste in Germany the emplacement of nuclear waste in deep geological formations is foreseen. Several safety principles are involved in the German safety requirements for a repository of heat-generating nuclear waste /BMU 2010/. The most significant ones are:

•Radionuclides and other contaminants have to be concentrated in thecontainment-providing rock zone and must be isolated from the biosphere aslong as possible.
•The risks from natural radiation exposure should be enhanced onlyinsignificantly by the release of radionuclides from waste disposal.

A multiple barrier system shall ensure the safe enclosure of radioactive waste. The system consists of the geological barrier (host rock), the geotechnical barriers (backfill and sealing elements) and the technical barriers (canisters and over packs) /BRA 2008/.

Three options of host rock are investigated in Europe: Rock salt, clay stone and crystalline rock. This thesis deals with the salt option. Rock salt is characterized by a natural porosity about 0.2 %, in which the pores are not connected continuous. The undisturbed rock salt is thight against fluids and gases. Voids in the host rock are able to be closed by time under compressive stress because of the viscoplastic material behaviour of rock salt. This circumstance is used for backfilling mine openings with crushed salt. Pores and pathways are able to be closed over the time if the crushed salt is compacted as results of the convergence from the host rock. Until the backfill satisfy its sealing capacity shafts and drifts of the disposal system could be closed with cement based plugs and seals. The integrity of the geological barrier and the stabilization of the disturbed rock zone at the contour shall be preserved by the sealing elements. In addition the inflow of solution and the release of radionuclides shall be decelerated