Editing Neutron flux (section)

==Artificial neutron flux==
{{Further |Neutron radiation}}

Artificial neutron flux refers to neutron flux which is man-made, either as byproducts from weapons or nuclear energy production or for a specific application such as from a [[research reactor]] or by [[spallation]]. A flow of neutrons is often used to initiate the [[nuclear fission|fission]] of unstable large nuclei. The additional neutron(s) may cause the nucleus to become unstable, causing it to decay (split) to form more stable products. This effect is essential in [[fission reactor]]s and [[nuclear weapon]]s.

Within a nuclear fission reactor, the neutron flux is the primary quantity measured to control the reaction inside. The flux shape is the term applied to the density or relative strength of the flux as it moves around the reactor. Typically the strongest neutron flux occurs in the middle of the reactor core, becoming lower toward the edges. The higher the neutron flux the greater the chance of a nuclear reaction occurring as there are more neutrons going through an area per unit time.

=== Reactor vessel wall neutron fluence ===
A [[reactor vessel]] of a typical nuclear power plant ([[Pressurized water reactor|PWR]]) endures in 40 years (32 full reactor years) of operation approximately 6.5×10<sup>19</sup> cm<sup>−2</sup> ([[Energy|''E'']] > 1 [[Electronvolt|MeV]]) of neutron fluence.<ref>[http://www.government.nl/documents-and-publications/reports/2012/07/12/kcb-rpv-safety-assessment.html Nuclear Power Plant Borssele Reactor Pressure Vessel Safety Assessment], p. 29, 5.6 Neutron Fluence Calculation.</ref> Neutron flux causes reactor vessels to suffer from [[neutron embrittlement]] and is a major problem with thermonuclear fusion like [[ITER]] and other magnetic confinement D-T reactors where fast (originally 14.06 MeV) neutrons damage equipment resulting in short equipment lifetime and huge costs and large volumes of radioactive waste streams.