A nuclear reactor is a type of power generator that produces electricity by causing and maintaining a nuclear chain reaction. In a nuclear chain reaction, atoms are bombarded with neutrons until they burst, producing smaller atoms and scattering neutrons. These scattered neutrons hit other atoms, causing them to split and release more neutrons. This process continues until all atoms have broken down. The more neutrons an atom has to begin with, the more volatile the reaction. Nuclear reactors harness the energy produced by the exploding atoms and turn it into electricity. Nuclear chain reactions are exothermic, i.e. heat is generated as the reaction runs its course. In a nuclear reactor, nuclear fuel is placed inside a vat of water, then bombarded with neutrons to induce a nuclear chain reaction. The heat created by the reaction causes the water to boil, and the resulting steam is piped over a turbine. The steam causes the turbine to turn, which powers up a generator, which in turn delivers electricity via power lines. In order to ensure that no water is wasted, the excess steam is run through a condenser, and the water is pumped back into the vat to be boiled.