Editing Fast-neutron reactor (section)

== Advantages ==

Fast reactors are widely seen as an essential development because of several advantages over moderated designs.<ref>{{cite web|url=https://whatisnuclear.com/fast-reactor.html|title = What is a fast reactor?}}</ref> The most studied and built fast reactor type is the [[sodium-cooled fast reactor]]. Some of the advantages of this design are discussed below; other designs such as the [[lead-cooled fast reactor]] and FMSR, Fast [[Molten Salt Reactor]]<ref>{{Cite journal |last1=Alsayyari |first1=Fahad |last2=Tiberga |first2=Marco |last3=Perkó |first3=Zoltán |last4=Kloosterman |first4=Jan Leen |last5=Lathouwers |first5=Danny |date=2021 |title=Analysis of the Molten Salt Fast Reactor using reduced-order models |journal=Progress in Nuclear Energy |volume=140 |pages=103909 |doi=10.1016/j.pnucene.2021.103909|doi-access=free |bibcode=2021PNuE..14003909A }}</ref> have similar advantages.

* A fission event creates more neutrons than in the thermal reactor. This gives flexibility and allows breeding of uranium or thorium.
* As {{chem|238|U}} absorbing a fast neutron has an 11% probability of fissioning, a significant percentage of the fission events in the reactor occur with this isotope.
* There is a fine balance between the production of neutrons from fission on the one hand, and the many processes that remove them from the equation on the other. If the temperature increases in a fast reactor, this will have two effects:
*# [[Doppler broadening]] of the neutron spectrum, and 
*# a very small increase in the physical size of the reactor core. 
: These two effects serve to reduce the reactivity because it allows more neutrons to escape the core, as was shown in a demonstration at EBR-II in 1986.<ref>{{cite web|url=https://www.youtube.com/watch?v=Sp1Xja6HlIU&t=355s&ab_channel=CapoRip|title=The Integral Fast Reactor|website=[[YouTube]]|date=17 June 2014 }}</ref> In this test, the additional heat was readily absorbed by the large volume of liquid sodium, and the reactor shut itself down, without operator intervention.

* Because sodium has a boiling point of {{convert|883| Celsius|sigfig=2}}, and lead has a boiling point of {{convert|1749| Celsius|sigfig=2}} but reactors operate typically around {{convert|500| Celsius|sigfig=2}} to {{convert|550| Celsius|sigfig=2}}, there is a large margin where the metals will stay liquid, and thermal increases can be easily absorbed, without any pressure increase. For the Chloride salts typically used in fast molten salt reactor designs the Sodium Chloride has a boiling point of {{convert|1,465| Celsius|sigfig=2}}<ref>{{Cite journal |last1=Mausolff |first1=Zander |last2=DeHart |first2=Mark |last3=Goluoglu |first3=Sedat |date=2021 |title=Design and assessment of a molten chloride fast reactor |journal=Nuclear Engineering and Design |volume=379 |pages=111181 |doi=10.1016/j.nucengdes.2021.111181|bibcode=2021NuEnD.37911181M |s2cid=234814975 }}</ref>
* As no water is present in the core at high temperatures, the reactor is essentially at atmospheric pressure. Most often, an inert gas blanket at a modest pressure (e.g. 0.5 atmospheres) is present to ensure that any leak results in mass transport to the outside of the reactor. This means that there is no pressure vessel with associated problems (high pressure systems are complex), nor will a leak from the reactor emit high pressure jets.
* The entire vessel being at atmospheric pressure, and the sodium is very hot, and can be allowed to remain at these temperatures even in shutdown, passive cooling (i.e. no pumping requirements) with air is possible. Accidents such as the Fukushima Daiichi nuclear accident <ref>{{cite web|url=https://world-nuclear.org/information-library/safety-and-security/safety-of-plants/fukushima-daiichi-accident.aspx|title=Fukushima Daiichi Accident - World Nuclear Association|website=world-nuclear.org}}</ref> are impossible with such a design.
* The higher temperature of the liquid metal or salt, and therefore the higher temperature of the steam generated by this coolant, allows a considerable increase in the electric generating efficiency (around 40% thermal efficiency, as opposed to 30%).<ref>https://factsheets.inl.gov/FactSheets/sodium-cooled-fast-reactor.pdf {{Webarchive|url=https://web.archive.org/web/20211125230913/https://factsheets.inl.gov/FactSheets/sodium-cooled-fast-reactor.pdf |date=2021-11-25 }} {{Bare URL PDF|date=March 2022}}</ref>
* Such reactors have the potential to significantly reduce the waste streams from nuclear power, while at the same time increasing vastly the fuel utilization.