Editing Nuclear reactor (section)

====By type of nuclear reaction====
All commercial power reactors are based on [[nuclear fission]]. They generally use [[uranium]] and its product [[plutonium]] as [[nuclear fuel]], though a [[thorium fuel cycle]] is also possible. Fission reactors can be divided roughly into two classes, depending on the energy of the neutrons that sustain the fission [[chain reaction]]:
* [[Thermal reactor|Thermal-neutron reactor]]s use slowed or [[thermal neutron]]s to keep up the fission of their fuel. Almost all current reactors are of this type. These contain [[neutron moderator]] materials that slow neutrons until their [[neutron temperature]] is ''thermalized'', that is, until their [[kinetic energy]] approaches the average kinetic energy of the surrounding particles. Thermal neutrons have a far higher [[Nuclear cross section|cross section]] (probability) of fissioning the [[fissile]] nuclei [[uranium-235]], [[plutonium-239]], and [[plutonium-241]], and a relatively lower probability of [[neutron capture]] by [[uranium-238]] (U-238) compared to the faster neutrons that originally result from fission, allowing use of [[low-enriched uranium]] or even [[natural uranium]] fuel. The moderator is often also the [[coolant]], usually water under high pressure to increase the [[boiling point]]. These are surrounded by a [[reactor vessel]], instrumentation to monitor and control the reactor, [[radiation shielding]], and a [[containment building]].
* [[Fast-neutron reactor]]s use [[fast neutron]]s to cause fission in their fuel. They do not have a [[neutron moderator]], and use less-moderating coolants. Maintaining a chain reaction requires the fuel to be more highly [[isotope separation|enriched]] in [[fissile]] material (about 20% or more) due to the relatively lower probability of fission versus capture by U-238. Fast reactors have the potential to produce less [[transuranic]] waste because all [[actinides]] are fissionable with fast neutrons,<ref>{{Cite journal | doi = 10.1007/BF00750983| title = Fast-reactor actinoid transmutation| journal = Atomic Energy| volume = 74| page = 83| year = 1993| last1 = Golubev | first1 = V. I.| last2 = Dolgov | first2 = V. V.| last3 = Dulin | first3 = V. A.| last4 = Zvonarev | first4 = A. V.| last5 = Smetanin | first5 = É. Y. | last6 = Kochetkov | first6 = L. A.| last7 = Korobeinikov | first7 = V. V.| last8 = Liforov | first8 = V. G.| last9 = Manturov | first9 = G. N.| last10 = Matveenko | first10 = I. P.| last11 = Tsibulya | first11 = A. M.| s2cid = 95704617}}</ref> but they are more difficult to build and more expensive to operate. Overall, fast reactors are less common than thermal reactors in most applications. Some early power stations were fast reactors, as are some Russian naval propulsion units. Construction of prototypes is continuing (see [[fast breeder]] or [[Generation IV reactor#Fast reactors|generation IV reactors]]).

In principle, [[fusion power]] could be produced by [[nuclear fusion]] of elements such as the [[deuterium]] isotope of [[hydrogen]]. While an ongoing rich research topic since at least the 1940s, no self-sustaining fusion reactor for any purpose has ever been built.