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Nuclear Facilities - Reportable Events - Decommissioning - Nuclear Accidents

nuclear safety

Nuclear fuel supply and waste management

Model of a fuel element with fuel rods Fuel Element ModelFuel Element Model Source: picture alliance / dpa | Maurizio Gambarini

Uranium is the most important element for nuclear energy use in nuclear reactors. Nuclear fuel supply encompasses all procedural steps from mining the uranium all the way to manufacturing the fuel elements.

A fuel element in a boiling or pressurised water reactor is composed of several fuel rods. A fuel rod is a metallic tube, about one to one and a half centimetres in diameter, and up to five metres long. These tubes contain the nuclear fuel, which consists of uranium oxide or, in the case of so-called MOX fuel elements, uranium and plutonium oxide. This material has a grey colour and is pressed into cylindrical pellets and sintered.

The fuel elements are used in the reactor, and must be disposed of once they are spent. The procedural steps for the treatment, reprocessing and disposal of spent fuel elements are collectively referred to as nuclear fuel disposal.

Nuclear fuel supply stages

  1. Mining of uranium-containing ores

  2. Extraction of the uranium from the rock in milling facilities

    The uranium content of the mined ores is typically 0.2 %. In a milling procedure the uranium is concentrated. The commercial product “Yellow Cake” is produced, which contains about 70 % to 75 % of uranium. The natural isotope composition of the uranium contained in the Yellow Cake is 0.7 % U-235 and 99.3% U-238

  3. Enrichment of the uranium isotope U-235 required for nuclear fission in light-water reactors

    Nuclear power plants with light water reactors need uranium with a share of 3 % to 5 % of the fissile isotope U-235. Therefore the isotope U-235 needs to be concentrated (“enriched”) in the uranium. For this purpose, the uranium is converted into the chemical compound uranium hexafluoride (UF6) which can easily be transferred into the gas phase. Only in the gas phase is it easy to enrich the uranium. Enrichment methods use the slight difference in mass of the U-235 and U-238 molecules of the UF6 to separate these two components. The product of the enrichment plant is UF6 whose U-235 share is ca. 3 % to 5 %

  4. Fabrication of fuel elements

    In a fuel element fabrication plant the uranium hexafluoride is converted into uranium dioxide (UO2). Tablets are pressed from UO2 powder that are sintered at temperatures above 1,700 °C, filled into cladding tubes made from zirconium alloys, and sealed gas-tight. This way single fuel rods are obtained that are assembled to fuel elements. Fuel elements of a pressurised water reactor contain about 500 kg uranium, those of a boiling-water reactor contain about 200 kg uranium.

In Germany, the following nuclear fuel supply plants are in operation:

Spent nuclear fuel management stages

Generally, fuel elements are used in reactors for three to four years. Due to the nuclear fissions, the share of the fissile U-235 decreases and radioactive fission products and significant amounts of plutonium generate, which is a new nuclear fuel. All activities to treat, reprocess and dispose of the spent fuel elements are collectively referred to as spent nuclear fuel management.

Two types of spent fuel element management are pursued:

  • Reprocessing including recovery and reuse of the usable shares of plutonium and uranium:
    The fuel elements are initially taken to an interim storage facility, where their activity decays. When they are reprocessed subsequently, reusable uranium and plutonium are separated from the radioactive fission products. Before they can be reused in a nuclear power plant, plutonium and uranium need to be reprocessed again to fuel elements. The radioactive fission products are solidified and then stored as radioactive waste.

or

  • Direct disposal:
    In direct disposal, the entire fuel element including the uranium and plutonium still contained therein is disposed of as radioactive waste after it has been stored intermediately in order for the short-lived radionuclides to decay and to reduce the heat generation that comes with the decay. For this purpose, the fuel elements are disassembled in a conditioning plant, placed into waste packages suitable for disposal and then disposed of as radioactive waste.

Since 2005, the law permits only the direct disposal of spent fuel elements in Germany.

In Germany

are being operated as spent nuclear fuel management installations.

A multi-stage search procedure to find the best possible site for a repository for high-level radioactive waste in Germany is taking place under the supervision of BASE. This repository is also intended to safely contain the spent fuel elements from German reactors in deep layers of rock.

More information

State of 2022.12.07

© Federal Office for the Safety of Nuclear Waste Management