Nuclear reactor

This article is about nuclear fission reactors. For nuclear fusion reactors, see Fusion power.
"Nuclear pile" redirects here. For nuclear stockpiles, see List of states with nuclear weapons.
From top, left to right
  1. Chicago Pile-1, the first nuclear reactor
  2. Shippingport Atomic Power Station, the first peacetime reactor
  3. HTR-10, a prototype to the first Generation IV reactor, HTR-PM
  4. The Convair NB-36H, the first aircraft to test an onboard reactor
  5. Operation Sea Orbit, the first nuclear-powered circumnavigation
  6. The Chernobyl sarcophagus, built to contain the effects of the 1986 disaster

A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. When a fissile nucleus like uranium-235 or plutonium-239 absorbs a neutron, it splits into lighter nuclei, releasing energy, gamma radiation, and free neutrons, which can induce further fission in a self-sustaining chain reaction. The process is carefully controlled using control rods and neutron moderators to regulate the number of neutrons that continue the reaction, ensuring the reactor operates safely, although inherent control by means of delayed neutrons also plays an important role in reactor output control. The efficiency of nuclear fuel is much higher than fossil fuels; the 5% enriched uranium used in the newest reactors has an energy density 120,000 times higher than coal.[1][2]

Nuclear reactors have their origins in the World War II Allied Manhattan Project.[note 1] The world's first artificial[note 2] nuclear reactor, Chicago Pile-1, achieved criticality on 2 December 1942.[5] Early reactor designs sought to produce weapons-grade plutonium for fission bombs, later incorporating grid electricity production in addition. In 1957, Shippingport Atomic Power Station became the first reactor dedicated to peaceful use; in Russia, in 1954, the first small nuclear power reactor APS-1 OBNINSK reached criticality. Other countries followed suit.

Heat from nuclear fission is passed to a working fluid coolant (water or gas), which in turn runs through turbines. In commercial reactors, turbines drive electrical generator shafts. The heat can also be used for district heating, and industrial applications including desalination and hydrogen production. Some reactors are used to produce isotopes for medical and industrial use. Reactors pose a nuclear proliferation risk as they can be configured to produce plutonium, as well as tritium gas used in boosted fission weapons. Reactor spent fuel can be reprocessed to yield up to 25% more nuclear fuel, which can be used in reactors again. Reprocessing can also significantly reduce the volume of nuclear waste, and has been practiced in Europe, Russia, India and Japan. Due to concerns of proliferation risks, the United States does not engage in or encourage reprocessing.[6]

Reactors are also used in nuclear propulsion of vehicles. Nuclear marine propulsion of ships and submarines is largely restricted to naval use. Reactors have also been tested for nuclear aircraft propulsion and spacecraft propulsion.

Reactor safety is maintained through various systems that control the rate of fission. The insertion of control rods, which absorb neutrons, can rapidly decrease the reactor's output, while other systems automatically shut down the reactor in the event of unsafe conditions. The buildup of neutron-absorbing fission products like xenon-135 can influence reactor behavior, requiring careful management to prevent issues such as the iodine pit, which can complicate reactor restarts. There have been two reactor accidents classed as an International Nuclear Event Scale Level 7 "major accident": the 1986 Chernobyl disaster and 2011 Fukushima disaster.

As of 2022, the International Atomic Energy Agency reported there are 422 nuclear power reactors and 223 nuclear research reactors in operation around the world.[7][8][9] The US Department of Energy classes reactors into generations, with the majority of the global fleet being Generation II reactors constructed from the 1960s to 1990s, and Generation IV reactors currently in development. Reactors can also be grouped by the choices of coolant and moderator. Almost 90% of global nuclear energy comes from pressurized water reactors and boiling water reactors, which use it as a coolant and moderator.[10] Other designs include heavy water reactors, gas-cooled reactors, and fast breeder reactors, variously optimizing efficiency, safety, and fuel type, enrichment, and burnup. Small modular reactors are also an area of current development. These reactors play a crucial role in generating large amounts of electricity with low carbon emissions, contributing significantly to the global energy mix.

  1. ^ "Nuclear Fuel Cycle Overview". World Nuclear Association. 20 May 2024. Retrieved 4 November 2024.
  2. ^ Science and Mathematics Education Research Group, University of British Columbia. "Physics Nuclear Physics: Nuclear Reactors" (PDF). Retrieved 4 November 2024.
  3. ^ L. Szilárd, "Improvements in or relating to the transmutation of chemical elements," Archived 21 June 2008 at the Wayback Machine British patent number: GB630726 (filed: 28 June 1934; published: 30 March 1936).
  4. ^ Davis, E. D.; Gould, C. R.; Sharapov, E. I. (2014). "Oklo reactors and implications for nuclear science". International Journal of Modern Physics E. 23 (4): 1430007–236. arXiv:1404.4948. Bibcode:2014IJMPE..2330007D. doi:10.1142/S0218301314300070. ISSN 0218-3013. S2CID 118394767.
  5. ^ Cite error: The named reference :0 was invoked but never defined (see the help page).
  6. ^ "Spent Fuel Reprocessing Options" (PDF). IAEA. Retrieved 30 August 2024.
  7. ^ "PRIS – Home". pris.iaea.org. Archived from the original on 11 February 2012. Retrieved 10 April 2019.
  8. ^ "RRDB Search". nucleus.iaea.org. Archived from the original on 18 September 2010. Retrieved 6 January 2019.
  9. ^ Oldekop, W. (1982), "Electricity and Heat from Thermal Nuclear Reactors", Primary Energy, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 66–91, doi:10.1007/978-3-642-68444-9_5, ISBN 978-3-540-11307-2, archived from the original on 5 June 2018, retrieved 2 February 2021
  10. ^ Region, CountryBy TypeBy (29 August 2024). "In Operation & Suspended Operation". PRIS. Retrieved 30 August 2024.


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