The Central Interim Storage Facility (ZZL) of Zwilag Zwischenlager Würenlingen AG consists of several interim storage buildings, a conditioning plant and an incineration/melting plant (plasma plant).

The interim storage buildings of Zwilag are used for the storage of spent fuel and radioactive waste of all categories for periods of several decades up until their final storage in a deep geological repository. The storage buildings include the container storage hall for spent fuel and vitrified high-level waste (vitrified residue packages) from reprocessing (HLW repository), the M storage building for intermediate-level waste (ILW repository) and the S storage building for low-level and intermediate-level waste (LLW/ILW repository). The interim storage facility also includes the reception building and the hot cell.

The conditioning plant is used for the treatment of low-level waste from the operation and decommissioning of Swiss nuclear power plants as well as other radioactive waste, such as from the Federal Collection Centre (waste from medicine, industry and research), in the event that such waste contains even a small proportion of alpha emitters.

The purpose of the plasma plant is to remove the organic fraction from the flammable and meltable low-level waste by incineration and to transfer the radioactive residues into an inert slag matrix.