[DoctorBeaver (OP)]

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?

[daveshorts]

There is possibly a point that you don't want to jam the control rods as you push them in, but otherwise I would have said it was artistic license. If you were in a room with a reactor that was going critical and were in a position to push in control rods, I would not rate you chances of survival for more than a couple of minutes anyway.

I think most nuclear reactors have several safety features before you get anywhere near pushing in control rods by hand. The reactor I visited in Hinkley Point in Somerset had the control rods, a system where you could release lots of boron balls (neutron absorbers) into the reactor in an emergency and if that didn't work a way of covering the whole thing in a boron slurry (which would stop the reactor ever working again).  This said I guess the Soviet Union was less worried about such things.

[DoctorBeaver (OP)]

You've confirmed my suspicions.

[Soul Surfer]

I know the calder hall reactors had emergency control rods which were continually kept from dropping into the reactor by motors and if there was any sort of cooling or other failure they would fall into the rector under their own gravity and stop the reaction. ( I saw this when i visited the place a couple of times many moons ago when I was at school. the later magnox and AGR's probably had similat safety features.

Learn, create, test and tell
evolution rules in all things
God says so!

[DoctorBeaver (OP)]

quote:Originally posted by Soul Surfer

...they would fall into the rector

Isn't that the Dean's job?

[tony6789]

Mabybe it would explode if it wre to be pushed down too fast

[gsmollin]

quote: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."