Question by ChunkyMunky: How are nuclear fission reactions controlled in nuclear power plants?
I was reading wikipedia and had more questions regarding nuclear power. How is the fuel in the rods, which last for about 6 years, controlled so it doesn’t explode or become totally spent instantly, like in a nuclear fission bomb? And, how do the rods, which are zirconium based, handle the intense heat given off? Or is it not as hot in the rods as I previously thought?
Best answer:
Answer by billrussell42
The rods moderate the neutron flux that hits them.
Nuclear fission of an atom releases about 2-3 neutrons per event. To keep the reaction going, at least one of those neutrons, on the average, has to initiate a new fission event. More than 1, say, 1.01, and the reaction starts to run away and will result in excess heat and possibly an explosion. Less than 1, say, 0.99, and the chain reaction dies down.
The moderator rods are moved into the reactor so they absorb more neutrons and slow things down, or pulled out a bit to speed things up by absorbing less neutrons. Motors move them in and out to keep the rate very close to 1.00.
The rods are made of material that absorbs neutrons, and that can also handle the high temperatures.
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