Importance in Nuclear Reactors
If a nuclear reactor happened to be prompt critical - even very slightly - the number of neutrons and power output would increase exponentially at a high rate. The response time of mechanical sytems like control rods is far too slow to moderate this kind of power surge. The control of the power rise would then be left to its intrinsic physical stability factors, like the thermal dilatation of the core, or the increased resonance absorptions of neutrons, that usually tend to decrease the reactor's reactivity when temperature rises; but the reactor would run the risk of being damaged or destroyed by heat.
However, thanks to the delayed neutrons, it is possible to leave the reactor in a subcritical state as far as only prompt neutrons are concerned: the delayed neutrons come a moment later, just in time to sustain the chain reaction when it is going to die out. In that regime, neutron production overall still grows exponentially, but on a time scale that is governed by the delayed neutron production, which is slow enough to be controlled (just as an otherwise unstable bicycle can be balanced because human reflexes are quick enough on the time scale of its instability). Thus, by widening the margins of non-operation and supercriticality and allowing more time to regulate the reactor, the delayed neutrons are essential to inherent reactor safety and even in reactors requiring active control.
Read more about this topic: Prompt Neutron
Famous quotes containing the words importance and/or nuclear:
“We have been told over and over about the importance of bonding to our children. Rarely do we hear about the skill of letting go, or, as one parent said, “that we raise our children to leave us.” Early childhood, as our kids gain skills and eagerly want some distance from us, is a time to build a kind of adult-child balance which permits both of us room.”
—Joan Sheingold Ditzion (20th century)
“The reduction of nuclear arsenals and the removal of the threat of worldwide nuclear destruction is a measure, in my judgment, of the power and strength of a great nation.”
—Jimmy Carter (James Earl Carter, Jr.)