Originally posted by DoctorBeaver
OK - I know the principle of controlled nuclear reactions & that the control rods are used to regulate the flow of particles. But why is it that in most, if not all, of the nuclear reactor crisis films I've seen, the rods have to be pushed in very slowly & carefully by hand? Why can't they just all be whacked right in to shut the reactor down? Or is this simply Hollywood licence?
I don't know what movies you've been watching, but in large, power nuclear reactors the control rods are not operated by hand. There are motors, and yes, normally the rods are moved very slowly in or out. The reason for the slowness, is that reactor critically is like balancing on a wire, so fast movements are not conducive to stable operation.
In the event of an emergency, the rods are forced in at a fast rate. This is called a SCRAM, and it's been the butt of many jokes in the nuclear industry. The origin of this word goes back to Enrico Fermi's first nuclear reactor. He stationed a man at the rope that was holding the safety rod out of the reactor. In the event that the reactor went into a runaway condition, he was to chop the rope with an axe so the safety rod could fall back into the reactor. Hence the name: Safety Control Rod Axe Man (SCRAM).
"F = ma, E = mc^2, and you can't push a string."