Nuclear power plants provide about 17 percent of the world's electricity. Some countries depend more on nuclear power for electricity than others. In France, for instance, about 75 percent of the electricity is generated from nuclear power, according to the International Atomic Energy Agency so that . In the United States, nuclear power supplies about 15 percent of the electricity overall, but some states get more power from nuclear plants than others. There are more than 400 nuclear power plants around the world, with more than 100 in the United States. In a reactor heat is produced by the fissioning or splitting of uranium atoms. A cooling medium takes up this heat and delivers it to the heat exchanger, where steam for the turbine is raised. When the uranium atoms split, there is radiation as well, the reactor and its cooling circuit must be heavily shielded against radiation hazards. Large electrical generating plants which provide most of our electricity all work on the same principle - they are giant steam engines. Power plants use heat supplied by a fuel to boil water and make steam, which drives a generator to make electricity. A generating plant's fuel, whether it is coal, gas, oil or uranium, heats water and turns it into steam. The pressure of the steam spins the blades of a giant rotating metal fan called a turbine. That turbine turns the shaft of a huge generator. Inside the generator, coils of wire and magnetic fields interact - and electricity is produced