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Technical barriers

As a passive safety device, technical barriers are a central component of reactor safety in German nuclear power plants. Several sequential technical barriers (multi-barrier system) are to retain the radioactive materials in normal operation and also in case of incidents. The barriers work independently of each other and at all levels of the effective safety concept.

The following technical barriers are available:

  • Fuel tablets

    The fuel is in a solid, ceramic substance, the fuel tablets, also referred to as pellets.

    In normal operational conditions, the major part of the radioactive materials generating in nuclear fission (activation and fission products) remain sealed in the heat-resistant crystal lattice of the fuel tablets.

  • Fuel rod cladding

    The fuel tablets are sealed in the fuel rods in cladding tubes made from a zirconium alloy "Zirkaloy". The fuel rod cladding is tight and pressure-resistant. It prevents the radioactive fission products from getting into the coolant.
    Several fuel rods are combined to fuel elements by means of a support structure. Depending on the reactor type, a varying amount of fuel elements is used in the reactor core.

  • Pressure retaining boundary

    The fuel elements are in a thick-walled reactor pressure vessel made from steel, where the nuclear chain reaction takes place in a controlled way. The heat is dissipated with water under pressure without boiling (pressurised water reactor) or as steam (boiling water reactor).
    The reactor pressure vessel and the associated piping for cooling water and steam form the so-called "pressure retaining boundary". It resists high temperatures and pressures and encloses the radioactive inventory during all normal and faulty modes of operation.

  • Reactor pressure vessel (reactor containment)

    The reactor pressure vessel is located inside a gas-tight containment. This containment serves to safely enclose the radioactive inventory, even in case of incidents.

  • Reactor building

    The reactor pressure vessel is in the reactor building which is ventilated and vented in a controlled way. The other purpose of the building is to protect against external influences, e.g. the influence of weather and pressure waves from explosion.

State of 2018.05.29

© Federal Office for the Safety of Nuclear Waste Management