Editing Fusion power (section)

=== Deuterium, tritium ===
{{main article|Deuterium–tritium fusion}}
[[File:Deuterium-tritium fusion.svg|thumb|upright=0.8|Diagram of the [[D+T|D-T]] reaction]]
The easiest nuclear reaction, at the lowest energy, is D+T:

:{{nuclide|Deuterium|link=yes}} + {{nuclide|Tritium|link=yes}} → {{nuclide|Helium|link=yes}} (3.5 MeV) + {{SubatomicParticle|10neutron|link=yes}} (14.1 MeV)

This reaction is common in research, industrial and military applications, usually as a neutron source. [[Deuterium]] is a naturally occurring [[isotope]] of hydrogen and is commonly available. The large mass ratio of the hydrogen isotopes makes their separation easy compared to the [[uranium enrichment]] process. [[Tritium]] is a natural isotope of hydrogen, but because it has a short [[half-life]] of 12.32 years, it is hard to find, store, produce, and is expensive. Consequently, the deuterium-tritium fuel cycle requires the breeding of tritium from [[lithium]] using one of the following reactions:

:{{SubatomicParticle|10neutron}} + {{nuclide|Lithium|6}} → {{nuclide|Tritium}} + {{nuclide|Helium}}
:{{SubatomicParticle|10neutron}} + {{nuclide|Lithium|7}} → {{nuclide|Tritium}} + {{nuclide|Helium}} + {{SubatomicParticle|10neutron}}

The reactant neutron is supplied by the D-T fusion reaction shown above, and the one that has the greatest energy yield. The reaction with <sup>6</sup>Li is [[exothermic reaction|exothermic]], providing a small energy gain for the reactor. The reaction with <sup>7</sup>Li is [[endothermic reaction|endothermic]], but does not consume the neutron. Neutron multiplication reactions are required to replace the neutrons lost to absorption by other elements. Leading candidate neutron multiplication materials are [[beryllium]] and [[lead]], but the <sup>7</sup>Li reaction helps to keep the neutron population high. Natural lithium is mainly <sup>7</sup>Li, which has a low tritium production [[Neutron cross section|cross section]] compared to <sup>6</sup>Li so most reactor designs use [[breeding blanket]]s with enriched <sup>6</sup>Li.

Drawbacks commonly attributed to D-T fusion power include:

* The supply of neutrons results in [[neutron activation]] of the reactor materials.<ref>{{Cite book|last1=Velarde|first1=Guillermo |title=Nuclear fusion by inertial confinement: a comprehensive treatise|last2=Martínez-Val|first2=José María|last3=Ronen|first3=Yigal|date=1993|publisher=CRC Press|isbn=978-0849369261|location=Boca Raton; Ann Arbor; London|language=en|oclc=468393053}}</ref><sup>:242</sup>
* 80% of the resultant energy is carried off by neutrons, which limits the use of direct energy conversion.<ref>{{cite journal |last1=Iiyoshi |first1=A |last2=Momota |first2=H. |last3=Motojima |first3=O. |display-authors=etal |date=October 1993 |title=Innovative Energy Production in Fusion Reactors |url=http://www.nifs.ac.jp/report/nifs250.html |url-status=dead |journal=National Institute for Fusion Science NIFS |pages=2–3 |bibcode=1993iepf.rept.....I |archive-url=https://web.archive.org/web/20150904055903/http://www.nifs.ac.jp/report/nifs250.html |archive-date=September 4, 2015 |access-date=February 14, 2012}}</ref>
* It requires the [[radioisotope]] tritium. Tritium may leak from reactors. Some estimates suggest that this would represent a substantial environmental radioactivity release.<ref>{{Cite web|title=Nuclear Fusion : WNA – World Nuclear Association|url=https://www.world-nuclear.org/information-library/current-and-future-generation/nuclear-fusion-power.aspx|access-date=October 11, 2020|website=www.world-nuclear.org}}</ref>

The [[neutron flux]] expected in a commercial D-T fusion reactor is about 100 times that of fission power reactors, posing problems for [[plasma facing material|material design]]. After a series of D-T tests at [[Joint European Torus|JET]], the vacuum vessel was sufficiently radioactive that it required remote handling for the year following the tests.<ref>{{cite journal|last=Rolfe|first=A. C.|title=Remote Handling JET Experience|journal=Nuclear Energy|date=1999|volume=38|issue=5|page=6|url=http://www.iop.org/Jet/fulltext/JETP99028.pdf|access-date=April 10, 2012|issn=0140-4067}}</ref>

In a production setting, the neutrons would react with lithium in the breeding blanket composed of lithium ceramic pebbles or liquid lithium, yielding tritium. The energy of the neutrons ends up in the lithium, which would then be transferred to drive electrical production. The lithium blanket protects the outer portions of the reactor from the neutron flux. Newer designs, the advanced tokamak in particular, use lithium inside the reactor core as a design element. The plasma interacts directly with the lithium, preventing a problem known as "recycling". The advantage of this design was demonstrated in the [[Lithium Tokamak Experiment]].