ATWS

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ATWS ( Anticipated Transient without Scram ) is the English and also the official name elsewhere for a nuclear power plant accident with an obstacle to heat removal from the reactor and simultaneous failure of the emergency shutdown .

The emergency shutdown of nuclear power plants is a relatively reliable component. Accordingly, officially there have only been a few precursor incidents to the ATWS so far. In 1981, for example, the reactor protection system at the Salem nuclear power plant in the US failed , that is, the control system that ensures automatic execution of the emergency shutdown. However, the operating staff was able to manually activate the emergency shutdown in good time, and the reactor was not previously running at full load .

If the emergency shutdown fails, there is an emergency measure for light water reactors, the so-called emergency boration with boric acid , which acts as a neutron poison and stops the chain reaction when the concentration in the reactor coolant increases . On March 1, 2006, an incident occurred at the Kozloduy nuclear power plant , which was rated 2 on the International Rating Scale for Nuclear Events (INES) and during which the reactor had to be shut down in part by means of emergency boring. However, only 22 of 60 shut-off rods were affected by the failure, and the triggering event - failure of one of the four primary circuit pumps - was a very mild transient.

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  1. INES 2 ACCIDENT AT KOZLODUY (PDF; 225 kB)
  • Main Department for the Safety of Nuclear Facilities (HSK): Periodic safety review for the Mühleberg nuclear power plant , 2002
  • Oekoinstitut Darmstadt: Assessment of the documents issued to obtain a definitive operating license for the Mühleberg NPP , 1991