A nuclear plant is based on steam production activating a turbine that is connected to an electricity generator, just like a coal or gas plant. But unlike a traditional facility, it burns no fuel. In order to produce steam, it uses the great amount of energy released from the fission (splitting) of the nucleus of specific atoms, usually of uranium.
Therefore, a nuclear plant is characterized by the “nuclear reactor”, inside which take place the “fission” reactions that release energy as heat. In turn, heat warms the so-called cooling fluid of the reactor, usually water, which allows the production of steam to activate the turbines.