What is nuclear energy and is it a viable resource?

Nuclear power is generated by splitting atoms to release the energy held at the core, or nucleus, of those atoms. This process, nuclear fission, generates heat that is directed to a cooling agent—usually water. The resulting steam spins a turbine connected to a generator, producing electricity.

About 450 nuclear reactors provide about 11 percent of the world's electricity. The countries generating the most nuclear power are, in order, the United States, France, China, Russia, and South Korea.

The most common fuel for nuclear power is uranium, an abundant metal found throughout the world. Mined uranium is processed into U-235, an enriched version used as fuel in nuclear reactors because its atoms can be split apart easily.

In a nuclear reactor, neutrons—subatomic particles that have no electric charge—collide with atoms, causing them to split. That collision—called nuclear fission—releases more neutrons that react with more atoms, creating a chain reaction. A byproduct of nuclear reactions, plutonium, can also be used as nuclear fuel.

Types of nuclear reactors

In the U.S. most nuclear reactors are either boiling water reactors, in which the water is heated to the boiling point to release steam, or pressurized water reactors, in which the pressurized water does not boil but funnels heat to a secondary water supply for steam generation. Other types of nuclear power reactors include gas-cooled reactors, which use carbon dioxide as the cooling agent and are used in the U.K., and fast neutron reactors, which are cooled by liquid sodium.

Nuclear energy history

The idea of nuclear power began in the 1930s, when physicist Enrico Fermi first showed that neutrons could split atoms. Fermi led a team that in 1942 achieved the first nuclear chain reaction, under a stadium at the University of Chicago. This was followed by a series of milestones in the 1950s: the first electricity produced from atomic energy at Idaho's Experimental Breeder Reactor I in 1951; the first nuclear power plant in the city of Obninsk in the former Soviet Union in 1954; and the first commercial nuclear power plant in Shippingport, Pennsylvania, in 1957. (Take our quizzes about nuclear power and see how much you've learned: for Part I, go here; for Part II, go here.)

Nuclear power, climate change, and future designs

Nuclear power isn't considered renewable energy, given its dependence on a mined, finite resource, but because operating reactors do not emit any of the greenhouse gases that contribute to global warming, proponents say it should be considered a climate change solution. National Geographic emerging explorer Leslie Dewan, for example, wants to resurrect the molten salt reactor, which uses liquid uranium dissolved in molten salt as fuel, arguing it could be safer and less costly than reactors in use today.

Others are working on small modular reactors that could be portable and easier to build. Innovations like those are aimed at saving an industry in crisis as current nuclear plants continue to age and new ones fail to compete on price with natural gas and renewable sources such as wind and solar.

The holy grail for the future of nuclear power involves nuclear fusion, which generates energy when two light nuclei smash together to form a single, heavier nucleus. Fusion could deliver more energy more safely and with far less harmful radioactive waste than fission, but just a small number of people—including a 14-year-old from Arkansas—have managed to build working nuclear fusion reactors. Organizations such as ITER in France and Max Planck Institute of Plasma Physics are working on commercially viable versions, which so far remain elusive.

Nuclear power risks

When arguing against nuclear power, opponents point to the problems of long-lived nuclear waste and the specter of rare but devastating nuclear accidents such as those at Chernobyl in 1986 and Fukushima Daiichi in 2011. The deadly Chernobyl disaster in Ukraine happened when flawed reactor design and human error caused a power surge and explosion at one of the reactors. Large amounts of radioactivity were released into the air, and hundreds of thousands of people were forced from their homes. Today, the area surrounding the plant—known as the Exclusion Zone—is open to tourists but inhabited only by the various wildlife species, such as gray wolves, that have since taken over.

In the case of Japan's Fukushima Daiichi, the aftermath of the Tohoku earthquake and tsunami caused the plant's catastrophic failures. Several years on, the surrounding towns struggle to recover, evacuees remain afraid to return, and public mistrust has dogged the recovery effort, despite government assurances that most areas are safe.

Other accidents, such as the partial meltdown at Pennsylvania's Three Mile Island in 1979, linger as terrifying examples of nuclear power's radioactive risks. The Fukushima disaster in particular raised questions about safety of power plants in seismic zones, such as Armenia's Metsamor power station.

Other issues related to nuclear power include where and how to store the spent fuel, or nuclear waste, which remains dangerously radioactive for thousands of years. Nuclear power plants, many of which are located on or near coasts because of the proximity to water for cooling, also face rising sea levels and the risk of more extreme storms due to climate change.