What is the theory behind nuclear reactors?

Answer 1

Neutron radiation (usually from a source such as Americium) strikes the atoms of a fissionable material (such as Uranium, specificaly the isotope U-235), and they are absorbed.

The abosorbtion of a neutron turns the material into an unstable isotope (for example, U-235 abosrobs a neutron and becomes U-236, which is highly unstable).

The new isotope breaks apart almost instantly, resulting in two smaller nuclei, the release of two or three neutrons, and a vast amount of energy, considering how many of these reactions occur in an instant, as even a very small piece of material is made of trillions, maybe even quadrillions of of atoms.

The newly released neutrons are free to fly off and be absorbed by other atoms, to continue the chain reaction. When enough neutrons are being released to sustain a reaction, the reactor is said to be critical.

The energy release by all of these constant, instantaneous, and extremely numerous reactions, is released as heat, which heats a body of water or other liquid surrounding the reactor core. This heated liquid turns to steam, which then rises, exerting mechanical force, which turns a turbine, which produces electicity. The steam passes through the tubine, where it passes over pipes through which cold water is being pumped from a nearby, separate body of water. The steam condensates and then, in liquid form, returns to the reactor core through gravity, where it is once again heated and continues to repeated this cycle.