Okay, just finished HBO’s Chernobyl and have fallen down the deep deep rabbit hole of trying to understand how nuclear reactors work, why water is needed, what a meltdown is and what happened at Chernobyl.
I think I have a good handle on it, but one thing I’m still not sure on: what initially “turns on” a nuclear reactor?
I get that the uranium fuel is encased in the zirconium rods, and that when it’s up and running the splitting uranium releases neutrons that split even more uranium and so on.
And I get that uranium is unstable on its own and eventually decays.
What I don’t understand is what begins the initial fission process that produces the heat that steams the water that turns the turbine.
I mean, the whole point of submerging the rods in water (or encasing them in graphite) is to ensure that the reactor doesn’t overheat, but what starts the reaction that such submerging or encasement is necessary? When a the rods are being assembled, they aren’t already producing that kind of heat, are they? If they are, then how is construction of a reactor even possible?
Again, how does a nuclear reactor “turn on”, and, by extension, how is it “turned off”?
In: Chemistry
Nothing. Or well, anything.
Uranium, on it own, occassionally emits a neutron. Normally, thd neutron flies off, and nothing much happens.
However, when you put the right amount of it, with the right KIND, in the right geometry together, a neutron is likely to hit another Uranium atom, which will split, releasing 2 (or more) neutrons. Those neutrons, because they are ALSO in the right (or wrong, depending on your perspective) shape/size/amount, will ALSO likely hit other atoms, releasing 4.. etc.
Just getting the uranium in the right orientation is enough to start it.
Alternately: you can have something JUST BARELY in the right orientation, and have it filled with things that harmlessly absorb neutrons (control rods). By moving those neutron absorbs in and out of the blib, you can control how much of that runaway process happens.
But really, once the pile is in the right orientation, the process will start on its own
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