Glossar

 

Repositories for HLW

Spent fuel (SF) from the Swiss nuclear power plants and vitrified fission product solutions from reprocessing will be disposed of in the high-level waste (HLW) repository.

The repository will also have tunnels for long-lived intermediate-level waste (ILW).

A ramp or a vertical shaft provide access to the disposal zone for high-level waste at a maximum depth of 700 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.

Image: Infel AG, Claudio Köppel

  1. Main facility SF/HLW
  2. ILW repository
  3. Pilot facility
  4. Test zones
  5. Access tunnel
  6. Ventilation shaft and construction shaft

The surface infrastructure of a geological repository consists of a surface facility with access road and, if possible, a rail link.

 

There are also shaft installations whose locations will be decided at a later stage.

OFA_HAA_2011

The surface facility serves as the portal to the repository. The waste is delivered here and prepared for emplacement. The facility includes an administration building, a visitors centre, various operations buildings and an encapsulation plant. In the latter, the spent fuel assemblies and vitrified high-level waste are removed from the transport and storage casks and loaded into disposal containers. The building has to fulfil very strict safety requirements. It is designed against massive impacts such as major earthquakes and aircraft crash. The surface facility also includes the access building to the repository, from where the waste is transported to the underground disposal zone.

An area of around 8 hectares is required for the surface facility, with a width of 150 metres (guide values). The actual site and the layout of the buildings are decided by the public and the authorities together with Nagra. The facility can be modified to fit with its surroundings; for example it could be located in an industrial zone near a population centre, at the edge of a forest and protected from view or on the site of a gravel-pit, partly hidden by sloping terrain or in the open landscape. 

Other components of the surface infrastructure include the shafts for ventilation and material transport. The shaft heads and associated small structures are located above the repository and require an area of around one hectare. Disposal areas are required for the material that will be excavated during construction of the access tunnel and the disposal tunnels. Some of this material can be re-used later for closing the repository.

Once the waste has been emplaced, the repository will be monitored for several decades. In this phase, part of the surface infrastructure is no longer required and will be demolished. Later, once the monitoring period is over, the remaining buildings will be demolished, with the exception of installations for long-term monitoring and marking.

Model of a site-specific layout for the surface facility of a deep repository for high-level waste. The location, layout and integration into the landscape will be decided together with the regional population. 

Model of the surface facility for the HLW repository. Image: maars, Zürich

  1. SF/HLW encapsulation plant
  2. Workshop
  3. Fire service building
  4. Cleaning plant for transport casks
  5. Treatment plant for operational waste and garages
  6. Access to the repository
  7. Electrical installations building
  8. Ventilation plant
  9. ILW encapsulation plant
  10. Processing plant for backfilling and sealing materials
  11. Administration centre
  12. Visitors centre
  13. Delivery terminal
  14. Train lock
  15. Vehicle lock

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.

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

High-level waste will be transported preferably by rail from the interim storage facility in Würenlingen to the surface facility of the repository.

Massive transport casks are used for this.

After an entry control, the transport casks with the high-level waste are brought to the encapsulation plant, where they are checked and removed from the rail waggon. In the next step, the waste is removed from the transport casks and loaded into thick-walled disposal containers that are then welded closed. The process is remotely controlled and carried out under very strict safety requirements.

The disposal 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

HAA Siba

  1. Glas matrix, containing radioactive material
  2. Metal container
  3. Backfill with bentonite
  4. Host rock

Operating procedures in the surface facility of a HLW repository

Film ©Nagra