Nuclear Reactors in the United States

There are 440 commercial nuclear reactors in the world with 92 of these in the United States. They utilize nuclear fission to create heat that causes steam to turn turbines that produce electricity. They use uranium for fuel. It is sealed into metal tubes named fuel rods that are bunched together into fuel assemblies. Hundreds of fuel assemblies make up the reactor core.

Water surrounds the fuel rods to cool the reactor and to moderate the neutrons that are produced by the chain reactions.

Control rods are inserted or withdrawn from the reactor core to slow or to increase the reaction.

In the United States, all the commercial reactors use normal water as a neutron moderator and coolant and are categorized as Light-water Reactors. They are either Pressurized Water Reactors (PWR) or Boiling Water Reactors (BWR).

Pressured Water Reactors keep the water from boiling by using high pressure. The reactor heats the water, which is then pumped through tubes into a heat exchanger which converts water from a different source into steam.

Boiling Water Reactors turn the water inside the reactor into steam which passes through pipes to the turbine. The steam subsequently liquifies and the water returns to the reactor to replicate the process.

Source: Office of Nuclear Energy, U.S. Department of Energy.