Briefly explain how nuclear fission is used to generate electricity. Be sure to use the terms "steam" and "turbine."

In general a process that releases heat can be harnessed to generate electricity. The heat is transferred to water, turning the water to steam. The expansion of water to steam is used to turn a turbine. The turbine turns a generator: a rotating coil of wire in a magnetic field, which induces an electric current according to Faraday's Law of Induction.
Back to the process that releases heat. Some electrical generation plants are heated by burning fossil fuels, but nuclear reactions can be used as well.
The most common fuel to use is uranium, specifically uranium that has been enriched in the uranium-235 isotope (most uranium is uranium-238). When a moving neutron strikes the nucleus of an atom of uranium-235, it forms unstable uranium-236. "Unstable" means the uranium-236 nucleus rapidly splits into two smaller nuclei. This splitting is fission. In the process, three more neutrons are released, along with a quantity of nuclear binding energy.
The released energy heats the water that bathes the reactor fuel, and the heat is transferred to pressurized water in a heat exchanger. This hot, pressurized water is vaporized to steam and used to turn the turbine. The heat exchanger is necessary because the water that cycles through the reactor itself is radioactive.
The neutrons that are released can be absorbed by other uranium-235 nuclei, causing them to undergo fission, releasing more energy and three neutrons apiece. This is a chain reaction. Various means are used to control the speed of the neutrons in order to maintain a steady rate of fission, rather than a catastrophic increase in which the number of reacting nuclei increases by a factor of three at each step! In addition, control rods are available to be lowered into the reactor, where they slow down or stop the chain reaction by absorbing the neutrons.

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