The Nuclear Energy Act specifies that low- and intermediate-level waste 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.
Model of a site-specific layout for the surface facility of a deep repository for low- and intermediate-level waste. The location, layout and integration into the landscape will be decided together with the regional population. (Image: maars, Zürich)
The repository for low- and intermediate-level waste (L/ILW) consists of a test area with a rock laboratory, a pilot facility and a main facility with large disposal caverns. These installations are located at a depth of around 400 metres and are linked to the surface by an access tunnel and a shaft.
Once the ramp and the shaft have been excavated, the first step will be to construct the rock laboratory. Here, the host rock at the disposal site will be investigated in detail for a period of around five years.
The pilot facility 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 transfer 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)