Emergency cooling

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Under emergency cooling is generally understood as measures for emergency cooling of an overheated, but not burning, the system to normal temperature. One can distinguish:

  • Improvised measures, for example to cool down an overheated gas boiler or oil storage tank (due to a defect or ambient heat) from the outside using extinguishing water from the fire brigade, to prevent an explosion and / or fire accident.
  • Stationary emergency cooling ("emergency cooling system") connected to systems, which is usually started automatically when requested or in certain cases also manually (at the push of a button or a switch, less often with laborious work). Frequent emergency cooling media are water and air; for certain reasons, however, other substances can also be used. For example, when water and sodium come into contact, hydrogen or oxyhydrogen is produced ; In a breeder reactor there is sodium in the cooling circuits, so water is not used as a coolant.

Emergency cooling in nuclear power plants

Since the Fukushima nuclear disaster in March 2011 at the latest, it has been known worldwide that nuclear fuel rods generate large amounts of decay heat even after the nuclear reactors have been switched off and that this has to be removed from the reactor core by a cooling system or emergency cooling system, otherwise it will melt after a while and large amounts of radioactive substances can get into the environment.

In light water reactors , emergency cooling is always carried out with water, the same substance as in the cooling circuit in normal operation. The emergency cooling water is located in large containers and is usually fed into the reactor circuit with pumps for safety in the event of line failures with several lines. There are two types of light water reactors:

  • In addition to the emergency cooling systems in the narrower sense, a pressurized water reactor (PWR) also has so-called emergency feed systems, which can cool it down via the secondary circuit if there is no or a small leak in the primary circuit (two-circuit operation). In the event of a large leak, the water that has escaped from the leak must be sucked in again from the containment sump after about twenty minutes at the latest and used for further cooling.
  • Boiling water reactors (BWR) have significantly larger water supplies for emergency cooling. If these are not sufficient for unforeseen reasons or the regular pumps fail, there is usually the possibility of drawing in water from the neighboring body of water using improvised mobile pumps. There is a similar possibility with the PWR, but usually only for the emergency feed systems.

If the emergency cooling is inadequate, there is a risk of core meltdown within a shorter period of time, even if the reactor is switched off. The supervisory authorities have so-called emergency cooling criteria, which define what the emergency cooling must do as a minimum so that at least the core geometry remains intact.

See also

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