Thermal-neutron reactor

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A thermal-neutron reactor is a nuclear reactor that uses slow or thermal neutrons. ("Thermal" does not mean hot in an absolute sense, but means in thermal equilibrium with the medium it is interacting with, the reactor's fuel, moderator and structure, which is much lower energy than the fast neutrons initially produced by fission.)

Most nuclear power plant reactors are thermal reactors and use a neutron moderator to slow neutrons until they approach the average kinetic energy of the surrounding particles, that is, to reduce the speed of the neutrons to low-velocity, thermal neutrons. Neutrons are uncharged, this allows them to penetrate deep in the target and close to the nuclei, thus scattering neutrons by nuclear forces, some nuclides are scattered large. [1]

The nuclear cross section of uranium-235 for slow thermal neutrons is about 1000 barns, while for fast neutrons it is in the order of 1 barn. [2] Therefore, thermal neutrons are more likely to cause uranium-235 to nuclear fission than to be captured by uranium-238. If at least one neutron from the U-235 fission strikes another nucleus and causes it to fission, then the chain reaction will continue. If the reaction will sustain itself, it is said to be critical, and the mass of U-235 required to produce the critical condition is said to be a critical mass.

Thermal reactors consist of the following:

See also

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<span class="mw-page-title-main">Sodium-cooled fast reactor</span> Type of nuclear reactor cooled by molten sodium

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<span class="mw-page-title-main">Nuclear reactor physics</span> Field of physics dealing with nuclear reactors

Nuclear reactor physics is the field of physics that studies and deals with the applied study and engineering applications of chain reaction to induce a controlled rate of fission in a nuclear reactor for the production of energy. Most nuclear reactors use a chain reaction to induce a controlled rate of nuclear fission in fissile material, releasing both energy and free neutrons. A reactor consists of an assembly of nuclear fuel, usually surrounded by a neutron moderator such as regular water, heavy water, graphite, or zirconium hydride, and fitted with mechanisms such as control rods which control the rate of the reaction.

<span class="mw-page-title-main">Neutron temperature</span> The kinetic energy of an unbound neutron

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92
U
nuclei – in other words, cause fission.

A pressurized heavy-water reactor (PHWR) is a nuclear reactor that uses heavy water (deuterium oxide D2O) as its coolant and neutron moderator. PHWRs frequently use natural uranium as fuel, but sometimes also use very low enriched uranium. The heavy water coolant is kept under pressure to avoid boiling, allowing it to reach higher temperature (mostly) without forming steam bubbles, exactly as for a pressurized water reactor. While heavy water is very expensive to isolate from ordinary water (often referred to as light water in contrast to heavy water), its low absorption of neutrons greatly increases the neutron economy of the reactor, avoiding the need for enriched fuel. The high cost of the heavy water is offset by the lowered cost of using natural uranium and/or alternative fuel cycles. As of the beginning of 2001, 31 PHWRs were in operation, having a total capacity of 16.5 GW(e), representing roughly 7.76% by number and 4.7% by generating capacity of all current operating reactors.

<span class="mw-page-title-main">Organic nuclear reactor</span> Nuclear reactor that uses organic liquids for cooling and neutron moderation

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References

  1. Squires, G. L. (2012-03-29). Introduction to the Theory of Thermal Neutron Scattering. Cambridge University Press. ISBN   978-1-107-64406-9.
  2. "Some Physics of Uranium". Archived from the original on March 3, 2008. Retrieved 2009-01-18.