Glossar

 

Repository for high-level waste

Spent fuel assemblies (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.

A ramp or a vertical shaft provide access to the disposal zone for high-level waste at a maximum depth of around 900 metres.

The pilot facility can also be used to monitor the behaviour of the safety barriers after the emplacement drifts in the main repository have been closed.

Image: Infel AG, Claudio Köppel

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

The surface infrastructure forms part of a deep geological repository.

A deep geological repository for radioactive waste also consists of facilities built at or close to the earth's surface. This "surface infrastructure" is required for the construction and operation of the repository.

OFA_HAA_2011

Model site-specific design of a surface facility for the high-level waste repository. The location, design and incorporation into the surrounding landscape will be determined in cooperation with the regional population. Image: maars, Zürich

The high-level waste repository comprises drifts with a diameter of 2.5 metres for the emplacement of canisters with spent fuel assemblies and vitrified high-level waste.

The functioning of the repository will be monitored in the pilot repository using a representative volume 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 canisters that are then welded closed. The process is remotely controlled and carried out under very strict safety precautions.

The disposal canisters are then loaded individually onto the tunnel railway.

The locomotive drives through the access tunnel to the underground emplacement drifts.

In the emplacement drift, the canister is loaded onto a plinth of clay blocks on an emplacement trolley and brought to the emplacement position.

Once in position, the disposal canister together with the clay blocks is deposited in the drift and the trolley is pulled back.

The canisters are emplaced individually one after another in the drift with spaces in between.

The drift is continuously backfilled with compacted bentonite granulate.

Once the emplacement phase is complete, the open accesses to the emplacement drifts 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 canisters 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 assemblies, the cladding containing the uranium pellets represents the first engineered barrier. Packaged in thick-walled metal canisters (second engineered barrier), the fuel assemblies are placed on a bentonite plinth in the emplacement drift and the entire drift is backfilled with granular bentonite (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 canisters 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 canister
  3. Bentonite backfill
  4. Host rock

Operating procedures in the surface facility of a HLW repository

Film ©Nagra

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