Nuclear power is power obtained from the nucleus of an atom, the central cluster of neutron and proton particles. Most conventional power (coal, natural gas) comes from chemical energy, which is the energy of atoms interacting among themselves.
Nuclear power is based on Einstein's famous equation, E=mc2, which says that matter can be turned into energy, a lot of energy. The actual process used is nuclear fission, in which the atomic nucleus is split, releasing energy. Nuclear fission is also used in the original nuclear bombs, as discussed in the history of plutonium.
A nuclear power plant has a central core containing an element that can undergo fission, usually plutonium or uranium. The element is in the form of metal fuel rods or pellets, and they are immersed in a coolant fluid such as water. The water absorbs energy, heats, and drives a steam turbine to produce electricity.
Safety and security are also major design elements of the modern nuclear power plant. The fissionable material is held in a strong pressure vessel and and outer containment shell to prevent radiation leaks. Security measures are to prevent theft of fissionable materials that could be used in a dirty nuclear bomb.
There were 437 active nuclear power plants in the world in 2013 according to the International Atomic Energy Agency having a total capacity of about 370 gigawatts. The number has stagnated for a few years, as new new reactors have been offset by closures in Japan and elsewhere. In the United States, approximately 19% of electricity comes from its 100 operational nuclear power plants according to the IAEA and the US Energy Information Administration. That figure is projected to remain stable for several decades.
Additional nuclear power plants are found on the naval vessels of the United States and other developed countries. These reactors provide propulsion as well as electrical power. The largest of these reactors, those on the large aircraft carriers, are comparable in size to reactors powering cities.
Clean Tech Implications
Nuclear power has supporters and detractors. Nuclear power does not produce conventional waste products in the manner of a power plant based on combustion. It does not generate carbon dioxide. The power source can be considered sustainable in the sense that the amount of uranium consumed is miniscule compared to the Earth's reserves of the metal. Future power plants may use thorium as a fuel, which is even more abundant.
A nuclear power plant has a smaller footprint than a solar plant, coal plant, or generally any other source of comparable power. The disturbance, pollution, and other side effects of constructing the plant, though, are comparable to or larger than construction projects of similar size.
The power output of a nuclear plant can be adjusted according to demand, unlike solar or wind, which are intermittent. Solar power is high during the day and zero at night, while wind power depends on vagaries of wind speed.
Nuclear power plants have also been a destination for weapons-grade plutonium extracted from decommissioned nuclear weapons. The plutonium is diluted to a lower grade and put to civilian use.
On the negative side of the ledger, nuclear power produces nuclear waste. When uranium or plutonium fissions, it creates a mixture of intermediate elements that are themselves radioactive to greater or lesser degrees. In some cases, the spent nuclear fuel is reprocessed and introduced as fuel into a reactor of a different design. However, in the end, radioactive waste must be contained and sequestered for generations or longer. (On the right: nuclear waste being contained in glass.)
The existence of nuclear fuel also creates the danger of this material being stolen or otherwise obtained by terrorists. Fuel for a power plant is not suitable for an explosive nuclear weapon, but it can be used to spread radiation with a dirty bomb. The fuel can also spill, radiation can leak and has, and other accidents can occur during mining and processing of the uranium.