Shutdown (reactor technology)
Shutting down a nuclear reactor means putting it into an operating state in which it is subcritical by at least the shutdown margin that is stipulated for this in its technical specification. There may be other conditions that must be met for the reactor to be considered shut down, e.g. B. that the key of the reactor control is kept safe and that no fuel movements or maintenance work on the control systems take place.
The shutdown margin is defined as a reactivity , often as Δ k / k (where k is the effective multiplication factor ) or sometimes in dollars (the change in reactivity that leads from critical to promptly critical state). The designation can mean two things: on the one hand, the margin by which the reactor is subcritical if all control rods are retracted and, on the other hand, the margin by which the reactor would be shut down in the event of a reactor shutdown . When preparing the technical specifications of the reactor, care must therefore be taken to ensure that the shutdown margin is defined in the most conservative way. Typical specified values for the shutdown margin are at Δ k / k in the range 0.3–0.5%.
For a cold shutdown (engl. Cold shutdown) the cooling system is also 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 does not boil or evaporate even with a complete pressure drop in the cooling circuit.
After a core meltdown , a cold shutdown is not possible because the structure of the fuel rods and the coolant circuit are destroyed and the remains react in an uncontrolled manner, even if the pressure and temperature meet the conditions for cold shutdown at least temporarily.
See also
Individual evidence
- ↑ Hans-Urs Zwicky, Sten Lundberg, nuclear fuel: holistic view of recent developments. Report prepared for the Federal Commission for the Safety of Nuclear Installations , Section 3.2.4: Shutdown Safety , Zwicky Consulting, Remigen 2006, http://www.bfe.admin.ch/php/modules/publikationen/stream.php?extlang=de&name= de_141863839.pdf
- ^ NRC definition of cold shutdown. http://www.nrc.gov/reading-rm/basic-ref/glossary/cold-shutdown.html