Editing Helium-3 (section)

== Human production ==
=== Tritium decay ===
{{See also|Tritium}}
Virtually all helium-3 used in industry today is produced from the radioactive decay of [[tritium]], given its very low natural abundance and its very high cost.

Production, sales and distribution of helium-3 in the United States are managed by the [[US Department of Energy]] (DOE) [[DOE Isotope Program]].<ref>{{cite web |title=Isotope Development & Production for Research and Applications (IDPRA) |url=http://science.energy.gov/np/research/idpra/ |website=US Department of Energy Office of Science |date=18 October 2018 |access-date=11 January 2019 |archive-date=19 October 2011 |archive-url=https://web.archive.org/web/20111019074945/http://science.energy.gov/np/research/idpra/ |url-status=live }}</ref>

While tritium has several different experimentally determined values of its [[half-life]], [[National Institute of Standards and Technology|NIST]] lists {{val|4500|8|u=days|fmt=commas}} ({{val|12.32|0.02|u=years}}).<ref>
{{Cite journal
 |author          = Lucas, L. L.
 |author2         = Unterweger, M. P.
 |name-list-style = amp
 |date            = 2000
 |title           = Comprehensive Review and Critical Evaluation of the Half-Life of Tritium
 |doi             = 10.6028/jres.105.043
 |pmid = 27551621
 |journal         = [[Journal of Research of the National Institute of Standards and Technology]]
 |volume          = 105
 |issue           = 4
 |pages = 541–549
 |pmc= 4877155
 }}</ref> It decays into helium-3 by [[beta decay]] as in this nuclear equation:

:{| border="0"
|- style="height:2em;"
|{{nuclide|Hydrogen|3|}}&nbsp;||→&nbsp;||{{nuclide|helium|3|charge=1+}}&nbsp;||+&nbsp;||{{math|{{SubatomicParticle|link=yes|Electron}}}}&nbsp;||+&nbsp;||{{math|{{SubatomicParticle|link=yes|Electron Antineutrino}}}}
|}
<!-- simpler
:<chem>^3_1H \to ^3_2{He^+} + {e^-} + \bar{\nu}_e + 18.6 keV</chem>
-->
Among the total released energy of {{val|18.6|u=keV}}, the part taken by [[electron]]'s kinetic energy varies, with an average of {{val|5.7|u=keV}}, while the remaining energy is carried off by the nearly undetectable [[electron antineutrino]]. 
[[Beta particles]] from tritium can penetrate only about {{convert|6.0|mm}} of air, and they are incapable of passing through the dead outermost layer of human skin.<ref>[https://web.archive.org/web/20130520184942/http://www.ehso.emory.edu/content-forms/3anuclidedatasafetysheets.pdf Nuclide safety data sheet: Hydrogen-3]. ehso.emory.edu</ref> The unusually low energy released in the tritium beta decay makes the decay (along with that of [[Isotopes of rhenium|rhenium-187]]) appropriate for absolute neutrino mass measurements in the laboratory (the most recent experiment being [[KATRIN]]).

The low energy of tritium's radiation makes it difficult to detect tritium-labeled compounds except by using [[liquid scintillation counting]].

Tritium is a radioactive isotope of hydrogen and is typically produced by bombarding lithium-6 with neutrons in a nuclear reactor. The lithium nucleus absorbs a neutron and splits into helium-4 and tritium. Tritium decays into helium-3 with a half-life of {{val|12.3|u=years}}, so helium-3 can be produced by simply storing the tritium until it undergoes radioactive decay. As tritium forms a stable compound with oxygen ([[tritiated water]]) while helium-3 does not, the storage and collection process could [[continuous process|continuously]] collect the material that [[outgas]]ses from the stored material.

Tritium is a critical component of [[nuclear weapons]] and historically it was produced and stockpiled primarily for this application. The decay of tritium into helium-3 reduces the explosive power of the fusion warhead, so periodically the accumulated helium-3 must be removed from warhead reservoirs and tritium in storage. Helium-3 removed during this process is marketed for other applications.

For decades this has been, and remains, the principal source of the world's helium-3.<ref>{{Cite web |url=http://www.srs.gov/general/news/factsheets/tritium_esrs.pdf |title=Savannah River Tritium Enterprise: Fact Sheet |access-date=2016-03-01 |archive-date=2016-12-22 |archive-url=https://web.archive.org/web/20161222012847/http://www.srs.gov/general/news/factsheets/tritium_esrs.pdf |url-status=live }}</ref> Since the signing of the [[START I]] Treaty in 1991 the number of nuclear warheads that are kept ready for use has decreased.<ref>Charmian Schaller [https://web.archive.org/web/20061029124748/http://afci.lanl.gov/aptnews/aptnews.mar1_98.html Accelerator Production of Tritium – That Could Mean 40 Years of Work]. Los Alamos Monitor. March 1, 1998</ref><ref>[http://www.ieer.org/sdafiles/vol_5/5-1/tritium.html Science for Democratic Action Vol. 5 No. 1] {{Webarchive|url=https://web.archive.org/web/20060927015706/http://www.ieer.org/sdafiles/vol_5/5-1/tritium.html |date=2006-09-27 }}. IEER. Retrieved on 2011-11-08;</ref> This has reduced the quantity of helium-3 available from this source. Helium-3 stockpiles have been further diminished by increased demand,<ref name=CRS>{{cite report | first1=Dana A. | last1=Shea | first2=Daniel | last2=Morgan | publisher=[[Congressional Research Service]] | title=The Helium-3 Shortage: Supply, Demand, and Options for Congress | id=7-5700 | url=https://www.fas.org/sgp/crs/misc/R41419.pdf | date=22 December 2010 | access-date=23 December 2015 | archive-date=4 March 2016 | archive-url=https://web.archive.org/web/20160304003156/http://www.fas.org/sgp/crs/misc/R41419.pdf | url-status=live }}</ref> primarily for use in neutron radiation detectors and medical diagnostic procedures. US industrial demand for helium-3 reached a peak of {{convert|70,000|L}} (approximately {{convert|8|kg}}) per year in 2008. Price at auction, historically about {{convert|100|$/l}}, reached as high as {{Convert|2000|$/l}}.<ref>[https://spectrum.ieee.org/physics-projects-deflate-for-lack-of-helium3 Physics Projects Deflate for Lack of Helium-3] . Spectrum.ieee.org. Retrieved on 2011-11-08.</ref>  Since then, demand for helium-3 has declined to about {{convert|6000|L}} per year due to the high cost and efforts by the DOE to recycle it and find substitutes. Assuming a density of {{Convert|114|g/m3}} at $100/l helium-3 would be about a thirtieth as expensive as tritium (roughly {{convert|880|$/g}} vs roughly {{convert|30000|$/g}}) while at $2000/l helium-3 would be about half as expensive as tritium ({{convert|17540|$/g}} vs {{convert|30000|$/g}}).

The DOE recognized the developing shortage of both tritium and helium-3, and began producing tritium by lithium irradiation at the [[Tennessee Valley Authority]]'s [[Watts Bar Nuclear Generating Station]] in 2010.<ref name=CRS/> In this process tritium-producing burnable absorber rods (TPBARs) containing lithium in a ceramic form are inserted into the reactor in place of the normal boron control rods<ref>[http://pbadupws.nrc.gov/docs/ML0325/ML032521359.pdf Tritium Production] {{Webarchive|url=https://web.archive.org/web/20160827030415/http://pbadupws.nrc.gov/docs/ML0325/ML032521359.pdf |date=2016-08-27 }} Nuclear Regulatory Commission, 2005.</ref> Periodically the TPBARs are replaced and the tritium extracted.

Currently only two commercial nuclear reactors (Watts Bar Nuclear Plant Units 1 and 2) are being used for tritium production but the process could, if necessary, be vastly scaled up to meet any conceivable demand simply by utilizing more of the nation's power reactors{{Citation needed|reason=It is not obvious that any reactor could use TPBARs|date=February 2024}}. 
Substantial quantities of tritium and helium-3 could also be extracted from the heavy water moderator in [[CANDU]] nuclear reactors.<ref name=CRS/><ref name=D2O>{{cite patent
 | inventor1-last = Sur
 | inventor1-first = Bhaskar
 | inventor2-last = Rodrigo
 | inventor2-first = Lakshman
 | inventor3-last = Didsbury
 | inventor3-first = Richard
 | title = System and method for collecting <sup>3</sup>He gas from heavy water nuclear reactors
 | issue-date = 2013
 | patent-number = 2810716
 | country-code = CA
 | publication-date = 30 September 2013
 | url = http://www.ic.gc.ca/opic-cipo/cpd/eng/patent/2810716/summary.html?type=number_search&tabs1Index=tabs1_1
 }} {{Webarchive|url=https://web.archive.org/web/20151223142855/http://www.ic.gc.ca/opic-cipo/cpd/eng/patent/2810716/summary.html?type=number_search&tabs1Index=tabs1_1 |date=23 December 2015 }}</ref> India and Canada, the two countries with the largest [[heavy water reactor]] fleet, are both known to extract tritium from moderator/coolant heavy water, but those amounts are not nearly enough to satisfy global demand of either tritium or helium-3.

As tritium is also produced inadvertently in various processes in [[light water reactor]]s (see the article on tritium for details), extraction from those sources could be another source of helium-3. If the annual discharge of tritium (per 2018 figures) at [[La Hague reprocessing facility]] is taken as a basis, the amounts discharged ({{convert|31.2|g}} at La Hague) are not nearly enough to satisfy demand, even if 100% recovery is achieved.
{{Annual discharge of tritium from nuclear facilities}}