Nuclear power

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fr:L'énergie nucléaire

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Nuclear power is the application of a controlled nuclear chain reaction (fission or fusion) to generate electrical power.

Nuclear fission is the form of nuclear power in common use today. A fissile nucleus of an atom (typically a heavy atom like uranium) is struck by a neutron, making it unstable enough to split into two pieces. This process consumes a small amount of mass which is converted directly into energy per Einstein's famous equation, E=mc2. There are several fissile isotopes in existence, but the two most commonly used are uranium-235 and plutonium-239.

Nuclear fusion is like the opposite of fission: instead of obtaining the energy when heavy atomic nuclei are split, this obtains the energy from when light atomic nuclei are smashed together. Like fission, fusion consumes a small amount of mass to produce a very large amount of energy. Solar energy is fundamentally a result of nuclear fusion reactions in the Sun, and fusion is also the principle behind the thermonuclear weapons, commonly referred to as hydrogen bombs.

Of these two forms of nuclear power, fusion is considered desirable over fission because it does not have the risk of meltdowns, does not create proliferation risks, and takes advantage of one of the most abundant substances in the universe: hydrogen. However, no controlled man-made fusion reaction sustained and powerful enough to generate electrical power has been achieved to date despite decades of research.

Conventional nuclear reactors use uranium oxide pellets placed in a heavy reactor vessel that uses water as the primary coolant. Because the coolant water must remain liquid in order to efficiently conduct heat from the core to the turbines, the reactor vessel is pressurized. This means that if the vessel or coolant pipes leak for any reason, the steam that results must be contained because it is radioactive, and a backup system must deliver liquidwater to the core lest it overheat and meltdown.

Because it does not rely on carbon-based fuel except in emergencies, nuclear power does not contribute to greenhouse gases. Also, nuclear power is by far the densest energy source known to man, meaning a single facility can easily provide electricity to a large community. However, there are a number of caveats:

  • Spent nuclear fuel contains a large amount of fissile material, but cannot be legally reprocessed into new fuel in the United States. This means a large amount of very radioactive material is produced and must be stored securely.
  • Mismanagement of the reactor (Chernobyl) or poor design (Three Mile Island, Fukushima) can result in radioactive substance release or even meltdown. Ideally, reactors should be designed to resist fissile material diversion and to shut down safely without electrical power, human intervention, or radioactive substance release. The history of the nuclear industry suggests that this is seldom the case with current technology.
  • Nuclear proliferation, or the use of uranium or plutonium in weapons, is an ongoing concern, particularly in Iran and North Korea. Preventing the widespread acquisition of nuclear weapons or even radioactive dirty bombs is a complex problem that must be addressed at multiple levels.

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