Nagra allocates the waste to different repository types for disposal.

Deep geological repository for spent fuel assemblies and vitrified fission product solutions from reprocessing (HLW/SF repository).

Deep geological repository for low- and intermediate-level waste (L/ILW repository).

A preliminary allocation of the alpha-toxic waste (ATW) to the HLW or L/ILW repository is undertaken, with the final decision being based on the results of the safety analyses for the planned disposal sites.

No deep geological disposal is required for waste with short half-lives (containing nuclides with half-lives shorter than 60 days or wastes that decay to below clearance level within 30 years of their production).

High-level waste (HLW)

Reprocessing of spent fuel recovers re-usable uranium and the activation product plutonium for further energy production.

Fission products and other activation products are separated out and melted together with additives to form a glass. The solidified glass blocks have to be disposed of as high-level waste.

Spent fuel not destined for reprocessing is also treated as high-level waste. It is held in interim storage for several decades and then emplaced in a deep geological repository.

A disposal container will hold two glass blocks from reprocessing. Image: Nagra

Spent fuel

Disposal of spent fuel assemblies (SF)

Fuel rods are used to supply energy in nuclear power plants.

Atomic nuclei in the fuel assemblies split into fission products, a process that yields energy and highly active substances. After three to five years in a reactor, the fuel assemblies are spent and require to be replaced as their content of fissile U-235 has become too low. They can either be disposed of directly or reprocessed. In the latter case, the uranium and plutonium contained in the fuel assemblies is recovered for further energy production. 

The Swiss reactor operators have contracts with foreign plants for reprocessing of around 1200 tons of spent fuel. This corresponds more or less to the volume produced in the five Swiss nuclear power plants in around 15 years. If spent fuel is not reprocessed in the future, it will require to be disposed of as high-level waste. 

By 2005, around 1200 tons - approximately thirty percent of the total spent fuel expected from the existing power plants - had been transported abroad for reprocessing. The wastes that are separated during this process have to be returned to Switzerland. The Nuclear Energy Act, which entered into force in February 2005, prohibits the further export of spent fuel for reprocessing until the year 2016.

Disposal container for spent fuel assemblies from boiling water reactors (Leibstadt and Mühleberg NPPs). Image: Nagra

Comparison: fresh and spent fuel assembly

Low- and intermediate-level waste (L/ILW)

Besides high-level waste, the nuclear power plants also produce low- and intermediate-level waste.

This waste is prepared for deep disposal either at the power plant sites or at the ZWILAG interim storage facility in Würenlingen. The plasma furnace at ZWILAG is used to melt various types of low-level waste, which are solidified to form a slag-type mass. 

Raw wastes from medicine, industry and research are processed into a form suitable for disposal at the Paul Scherrer Institute or at ZWILAG and are then stored in the Federal Government’s interim storage facility (BZL) in Würenlingen. 

Reprocessing of spent fuel assemblies also produces low- and intermediate-level waste, for example structural components of the fuel assemblies.

Reprocessing of spent fuel elements also produces low- and intermediate-level waste (e.g. structural components of the fuel elements).

Waste categories

For the purpose of disposal, the Nuclear Energy Ordinance (Article 51) divides radioactive waste into the following categories:

High-level waste (HLW)

  • Spent fuel assemblies (SF) not destined for reprocessing
  • Vitrified fission product solutions from reprocessing of spent fuel 

Alpha-toxic waste (ATW), with a content of alpha-emitters exceeding a value of 20,000 Becquerels per gram of conditioned waste

Low- and intermediate-level waste (L/ILW)

  • All other radioactive waste