Repository for low- and intermediate-level waste

The Nuclear Energy Act specifies that low- and intermediate-level waste (L/ILW) has to be disposed of in a deep geological repository.

The facility will have caverns capable of accommodating a volume of around 100 000 cubic metres of packaged waste.

A vertical shaft or a tunnel provide access to the disposal caverns for low- and intermediate-level waste at a maximum depth of around 600 metres.

The caverns can be completely backfilled after several decades. Once the main repository has been closed, the behaviour of the safety barriers can continue to be monitored in the pilot repository.

Image: Infel AG, Claudio Köppel 

  1. Main repository L/ILW
  2. Pilot repository
  3. Test area
  4. Access tunnel
  5. 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.

Model site-specific design of a surface facility for the low- and intermediate-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 repository for low- and intermediate-level waste (L/ILW) consists of a test area, a pilot repository and a main repository with large disposal caverns.

The underground facilities are located at a depth of around 400 metres and are linked to the surface by an access tunnel and a shaft.  

Once the exploratory tunnel and shaft have been excavated, the first step will be to construct the facility for underground geological investigations. Here, the host rock at the disposal site will be investigated in detail for a period of around five years. 

The pilot repository is a smaller disposal cavern in which the first waste containers will be emplaced. These will be monitored during the entire operational and monitoring phase. 

The main repository consists of several large disposal caverns in which the L/ILW is stacked in concrete containers. 

The tunnels and caverns are equipped with a rail system and cranes to allow the emplacement process to be carried out remotely. 

Depending on the particular conditions at the site, it may be possible to construct some of the operational and waste reception facilities beneath the surface.

The drums with the conditioned low- and intermediate-level waste are delivered to the surface facility of the repository preferably by rail.

After an entry control, the drums are transported to the transloading station where they are checked and then loaded into prefabricated disposal containers made of concrete. These are filled with cement mortar.

The containers are transported via the access tunnel to the disposal caverns using the tunnel railway.

From there, the containers are transferred to their emplacement position using a travelling crane and are stacked on top of one another. 

The caverns are backfilled stepwise with a special mortar and later sealed.

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 mortar (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.

Model of a disposal container for low- and intermediate-level waste. Image: Nagra

Operating procedures in the surface facility of a L/ILW repository

Film ©Nagra

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