The nuclear power plants are the largest producers of radioactive waste.
The fission and activation products from spent nuclear fuel represent high-level waste. Operational waste and decommissioning waste arising from the dismantling of the nuclear power plants require to be disposed of as low- and intermediate-level waste.
In the field of nuclear technology, the nuclear fuel cycle includes all steps and processes from mining of uranium ore up to waste disposal.
Once ore has been mined, uranium-235 has to be enriched to produce new fuel elements. Spent fuel is either reprocessed, i.e. components that are still usable remain in the fuel cycle, or is disposed of directly following a period of interim storage.
Reprocessing of fuel elements is a sequence of procedures that separates out various components of the spent fuel.
Spent fuel is a mixture of around 4 percent highly active fission products, 95 percent uranium (with just 1 percent fissile uranium-235) and 1 percent plutonium. The uranium and plutonium can be used to manufacture new fuel elements and the fission products are treated as high-level waste. They are immobilised in a low-solubility glass matrix, making them suitable for transport and storage. After reprocessing abroad, the separated wastes have to be taken back by Switzerland.
Up to 2005, around 1200 tonnes of spent fuel were transported for reprocessing in France and the UK. There is currently a moratorium on reprocessing until 2016 and no more fuel elements are being transported abroad.
In addition to high-level waste, low- and intermediate-level waste is produced in the nuclear power plants.
It consists, for example, of contaminated protective clothing, cleaning materials, tools, machine components, concentrated effluents, ion-exchange resins, filters from cleaning systems and activated reactor components.
Operational waste being prepared for storage at Mühleberg NPP. Image: Mühleberg NPP
During reactor operation, components can become radioactive (activation) or contaminated with radioactive substances (contamination).
For example, the reactor pressure vessel and its internals and the biological shield (protective concrete wall) are activated by neutron radiation during reactor operation and have to be disposed of as low- and intermediate-level waste after the decommissioning of the nuclear power plant. Components that are contaminated with radioactive substances either have to be cleaned (decontaminated) or disposed of as waste.
The Niederaichbach power plant in Bavaria (Germany) during dismantling. The reactor has already been removed. Depending on their activation, the surrounding installations will also have to be disposed of as radioactive materials. Image: Karlsruhe Research Center