Shutdown (nuclear reactor)

Disable a nuclear reactor is to convert it into an operating state in which he is at least the Abschaltmarge subcritical, which is set in its technical specification for this. There may be other conditions that must be met before the reactor is considered to be switched off, for example, that the key of the reactor control is securely stored and held no fuel movements and maintenance of the control systems.

Defines the Abschaltmarge as a reactivity that often? K / k (where k is the effective multiplication factor means ), or sometimes in dollars ( the reactivity change for the prompt critical state results from the critical ). The term can mean two things: first, the margin by which the reactor is subcritical when all control rods are retracted, and the other, the margin by which the reactor would be shut down in the event of a reactor scram. When you create the technical specifications of the reactor must therefore be taken to ensure that the Abschaltmarge is defined on the most conservative way. Typical values ​​for the specified Abschaltmarge are in? K / k in the range 0.3-0.5 %.

In a cold shutdown ( Sheet cold shutdown ) is also the cooling system of the reactor to atmospheric pressure and the temperature is below about 95 ° C (200 ° F as defined by the American NRC) This temperature is so low that the cooling water in a light water reactor itself a total pressure drop in the cooling cycle does not boil or evaporate.

For a core melt no cold shutdown is possible because the structure of the fuel rods and the coolant circuit will be destroyed and the remains react uncontrollably, even when the pressure and temperature at least temporarily meet the conditions of the cold shutdown.