Safety Barriers

A multi-barrier approach ensures the long-term isolation of radioactive waste and is the adopted solution of preference for radioactive waste management. The Engineered Barrier System (EBS) is one part of this passive multi-barrier system approach and it refers to all barriers introduced through technological (engineered) activities. It is complemented by the natural barrier, also referred to as the geological barrier or geosphere.

 Components of the EBS for High Level Waste (HLW) and Spent Fuel (SF)

In a deep geological repository, safe long-term containment of the waste is provided by a system consisting of three engineered barriers and one geological barrier.

In the case of spent fuel, the cladding containing the uranium pellets represents the first engineered barrier. Packaged in thick-walled metal containers (second engineered barrier), the fuel elements are placed on a bentonite plinth in the disposal tunnel and the entire tunnel is backfilled with bentonite granulate (third engineered barrier). Together with the overlying formations, the host rock forms the geological barrier.

High-level fission product solutions from reprocessing are immobilised in a glass matrix that corrodes extremely slowly. The metal containers and the bentonite backfill again represent the other two engineered barriers

The Grimsel Full-scale Engineered Barriers Experiment (FEBEX) project has been examining the emplacement of a steel canister within a bentonite backfilled tunnel. A more detailed overview from the Swiss approach is shown below:

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 Components of the EBS for Low/Intermediate Level Waste (L/ILW)

The repository for low- and intermediate-level waste has four different safety barriers - three engineered and one geological.

The waste is solidified in a matrix and enclosed in drums (first engineered barrier).

Several of these drums are placed in a concrete container which is filled with cement (second engineered barrier).

The concrete containers are stacked on top of and adjacent to one another in large caverns and the spaces between the containers are backfilled with a special mortar (third engineered barrier).

Together with the overlying formations, the host rock forms the geological barrier.

As the EBS for L/ILW waste is constructed mostly from concrete, the effect of such a large cementitous mass on the rock and water systems is being investigated directly by in situ Grimsel projects such as Gas Migration in EBS and Geosphere (GMT), Hyperalkaline Plume in Fractured Rock (HPF) and Long-Term Cement Studies (LCS).

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The GTS underground facilities are also available to interested 3rd parties for underground testing and research. The GTS offers cost-effective access to a fully developed, well characterised underground research facility with round the year logistical support - please contact Dr. Ingo Blechschmidt, Head of the Grimsel Test Site, for further details.

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