Geological repository for high-level waste

A ramp or a vertical shaft will provide access to the waste emplacement zone at a depth between 400 and 900 metres. The pilot facility can also be used to check the behaviour of the safety barriers during a monitoring phase after the disposal tunnels in the main facility have been closed.

1. Access tunnel

2. Disposal tunnels for spent fuel and vitrified high-level waste

3. Rock laboratory

4. Pilot facility

5. Disposal tunnels for long-lived intermediate-level waste

6. Shaft

The surface structures of a high-level waste repository will require an area of around 200 by 400 metres.

The buildings at the surface consist of a reception facility where the waste arrives in transport containers, a transloading station and a packaging plant. There will also be an administration building with a visitors' centre, buildings for operation and maintenance of the repository and an access tunnel to the underground disposal zone. The shaft head will be located to one side and will require an area of around 100 by 100 metres.

The surface facilities can be modified to fit with the particular environment in which they are located.

Dumping areas will be required for the excavated material. Some of this material can be used later for closure of the repository.

The repository site will be accessed by road and rail links.

The high-level waste repository comprises disposal tunnels with a diameter of 2.5 metres for the emplacement of containers with spent fuel and vitrified high-level waste.

The functioning of the repository will be monitored in the pilot facility using a representative component of the waste.

Investigations relating to the construction and operation of the repository are carried out in the test area with a rock laboratory.

All disposal zones are located at a depth of around 600 metres. Access is via a tunnel and a shaft.

High-level waste is transported by rail from the interim storage facility in Würenlingen to the repository site.

Following inspection, the containers with the high-level waste are unloaded from the railway wagon in the packaging plant. The waste is repackaged and welded into thick-walled disposal containers.

The containers are then loaded individually onto the tunnel railway.

The locomotive drives through the access tunnel to the underground disposal tunnels.

In the disposal tunnel, the container is loaded onto a support of clay blocks on an emplacement trolley and brought to the emplacement position.

Once in position, the container resting on the clay blocks is deposited in the tunnel and the trolley is pulled back.

The containers are placed individually one after another in the tunnel with spaces in between.

The tunnel is continuously backfilled with compacted bentonite granulate.

Once the emplacement phase is complete, the open accesses to the disposal tunnels are backfilled and sealed.

When the decision is made to finally close the entire facility, open tunnels and the shaft will be backfilled and sealed.

The disposal containers can be retrieved at any time.

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.

Safety barriers in a repository for high-level waste.

1. Glas matrix, containing radioactive material

2. Metal container

3. Backfill with bentonite

4. Host rock