View source for Heavy water

{{Short description|Form of water}}
{{Distinguish|Hard water|Tritiated water}}
{{Use dmy dates|date=December 2022}}
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| Name = 
| ImageFileL1 = Heavy-water-3D-vdW.svg
| ImageFileL1_Ref = {{chemboximage|correct|??}}
| ImageSizeL1 = 150
| ImageNameL1 = Spacefill model of heavy water
| ImageFileR1 = Heavy water.svg
| ImageSizeR1 = 100
| IUPACName = ({{sup|2}}H{{sub|2}})Water<ref>{{RedBook2005|page=306}}</ref>
| SystematicName = 
| OtherNames = {{unbulleted list
 |Deuterium oxide<ref name=parpart1935>{{cite journal|last1=Parpart|first1=Arthur K.|title=The permeability of the mammalian erythrocyte to deuterium oxide (heavy water)|journal=Journal of Cellular and Comparative Physiology|date=December 1935|volume=7|issue=2|pages=153–162|doi=10.1002/jcp.1030070202}}</ref>
 |Water-''d''<sub>2</sub><ref name=svishchev1994>{{cite journal|last1=Svishchev|first1=I. M.|last2=Kusalik|first2=P. G.|title=Dynamics in liquid water, water-d2, and water-t2: a comparative simulation study|journal=The Journal of Physical Chemistry|date=January 1994|volume=98|issue=3|pages=728–733|doi=10.1021/j100054a002}}</ref>
 |Dideuterium monoxide
 |Deuterated water<ref name="auto">{{Cite web|last=PubChem|title=Deuterium oxide|url=https://pubchem.ncbi.nlm.nih.gov/compound/24602|access-date=22 April 2021|website=pubchem.ncbi.nlm.nih.gov|language=en}}</ref>}}
| Section1 = {{Chembox Identifiers
| CASNo = 7789-20-0
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 24602
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 1232306
| ChemSpiderID = 23004
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| UNII = J65BV539M3
| UNII_Ref = {{fdacite|correct|FDA}}
| EINECS = 232-148-9
| KEGG = D03703
| KEGG_Ref = {{keggcite|correct|kegg}}
| MeSHName = Deuterium+Oxide
| ChEBI = 41981
| ChEBI_Ref = {{ebicite|correct|EBI}}
| RTECS = ZC0230000
| Gmelin = 97
| SMILES = [2H]O[2H]
| StdInChI = 1S/H2O/h1H2/i/hD2
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| StdInChIKey = XLYOFNOQVPJJNP-ZSJDYOACSA-N
| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
}}
| Section2 = {{Chembox Properties
| Formula = {{Chem|D|2|O}}
| MolarMass = 20.0276 g mol{{sup|−1}}
| Appearance = Colorless liquid
| Odor = Odorless
| Density = 1.107 g mL{{sup|−1}}
| MeltingPtK = 276.97
| BoilingPtC = 101.4
| Solubility = Miscible
| LogP = −1.38
| RefractIndex = 1.328
| Viscosity = 1.25 mPa s (at 20&nbsp;°C)
| Dipole = 1.87 D
}}
| Section3 = {{Chembox Hazards
| NFPA-H = 1
| NFPA-F = 0
| NFPA-R = 0
}}
| Section4 = 
| Section5 = 
| Section6 = 
}}
'''Heavy water''' ('''deuterium oxide''', '''{{Chem|2|H|2|O}}''', '''{{Chem|D|2|O}}''') is a form of [[water (molecule)|water]] in which hydrogen atoms are all [[deuterium]] ({{Chem|2|H}} or D, also known as ''heavy hydrogen'') rather than the common hydrogen-1 [[isotope]] ({{Chem|1|H}}, also called ''protium'') that makes up most of the hydrogen in normal water.<ref name="auto"/> The presence of the heavier isotope gives the water different nuclear properties, and the increase in mass gives it slightly different physical and chemical properties when compared to normal water.

Deuterium is a heavy [[Isotopes of hydrogen|hydrogen isotope]]. Heavy water contains deuterium atoms and is used in [[nuclear reactor]]s. [[Semiheavy water]] (HDO) is more common than pure heavy water, while heavy-oxygen water is denser but lacks unique properties. Tritiated water is radioactive due to [[tritium]] content.

Heavy water has different physical properties from regular water, such as being 10.6% denser and having a higher melting point. Heavy water is less [[Dissociation (chemistry)|dissociated]] at a given temperature, and it does not have the slightly blue color of regular water. It can taste slightly sweeter than regular water, though not to a significant degree. Heavy water affects biological systems by altering enzymes, hydrogen bonds, and cell division in [[eukaryote]]s. It can be lethal to multicellular organisms at concentrations over 50%. However, some [[prokaryotes]] like [[bacteria]] can survive in a heavy hydrogen environment. Heavy water can be toxic to humans, but a large amount would be needed for poisoning to occur.

The most cost-effective process for producing heavy water is the [[Girdler sulfide process]]. Heavy water is used in various industries and is sold in different grades of purity. Some of its applications include [[nuclear magnetic resonance]], [[infrared spectroscopy]], [[neutron moderation]], [[neutrino detection]], metabolic rate testing, [[neutron capture therapy]], and the production of radioactive materials such as [[plutonium]] and tritium. <!--In nuclear magnetic resonance, it is used to prevent interference with hydrogen-1 signals. In organic chemistry, it helps in preparing specifically labeled isotopologues. In infrared spectroscopy, it replaces water to prevent overlapping bands in protein spectra. Heavy water is used in nuclear reactors as a neutron moderator, allowing the use of natural uranium instead of enriched uranium. It is also employed in neutrino detectors like the Sudbury Neutrino Observatory, where it helps to detect different types of neutrinos. In metabolic rate testing, heavy water is used in the doubly labeled water test to measure body water turnover. Lastly, tritium, an isotope of hydrogen, can be produced in heavy water-moderated reactors, though it requires high neutron fluxes and isotope separation.-->

== Composition ==

The deuterium [[Atomic nucleus|nucleus]] consists of a [[neutron]] and a [[proton]]; the nucleus of a protium (normal hydrogen) atom consists of just a proton. The additional neutron makes a deuterium atom roughly twice as heavy as a protium atom.

A molecule of heavy water has two deuterium atoms in place of the two protium atoms of ordinary water. The term heavy water as defined by the [[International Union of Pure and Applied Chemistry|IUPAC]] Gold Book<ref>{{GoldBookRef|title=heavy water|file=H02758}}</ref> can also refer to water in which a higher than usual proportion of hydrogen atoms are deuterium. For comparison, [[Vienna Standard Mean Ocean Water]] (the "ordinary water" used for a deuterium standard) contains about 156 deuterium atoms per million hydrogen atoms; that is, 0.0156% of the hydrogen atoms are {{sup|2}}H. Thus heavy water as defined by the Gold Book includes [[semiheavy water]] (hydrogen-deuterium oxide, HDO) and other mixtures of {{chem|D|2|O}}, {{chem|H|2|O}}, and HDO in which the proportion of deuterium is greater than usual. For instance, the heavy water used in [[CANDU reactor]]s is a highly enriched water mixture that is mostly deuterium oxide {{chem|D|2|O}}, but also some hydrogen-deuterium oxide and a smaller amount of ordinary water {{chem|H|2|O}}. It is 99.75% enriched by hydrogen atom-fraction; that is, 99.75% of the hydrogen atoms are of the heavy type; however, heavy water in the Gold Book sense need not be so highly enriched. The weight of a heavy water molecule, however, is not very different from that of a normal water molecule, because about 89% of the mass of the molecule comes from the single [[oxygen]] atom rather than the two hydrogens.

Heavy water is not [[Radioactive decay|radioactive]]. In its pure form, it has a density about 11% greater than water but is otherwise physically and chemically similar. Nevertheless, the various differences in deuterium-containing water (especially affecting the biological properties) are larger than in any other commonly occurring [[isotopologue|isotope-substituted compound]] because deuterium is unique among heavy [[stable isotope]]s in being twice as heavy as the lightest isotope. This difference increases the [[bond energy|strength]] of water's hydrogen–oxygen bonds, and this in turn is enough to cause differences that are important to some biochemical reactions. The human body naturally contains deuterium equivalent to about five grams of heavy water, which is harmless. When a large fraction of water (> 50%) in higher organisms is replaced by heavy water, the result is [[Cell (biology)|cell]] dysfunction and death.<ref>{{Cite journal|pmid=10535697 |title=Pharmacological uses and perspectives of heavy water and deuterated compounds |author1=D. J. Kushner |author2=Alison Baker |author3=T. G. Dunstall |journal=Can. J. Physiol. Pharmacol. |volume=77 |issue=2 |pages=79–88 |date=1999 |doi=10.1139/cjpp-77-2-79}}</ref>

Heavy water was first produced in 1932, a few months after the discovery of deuterium.<ref>{{cite web| url = http://www.columbia.edu/cu/chemistry/fac-bios/brus/group/pages/urey.html| title = Harold Clayton Urey (1893–1981)|website = [[Columbia University]]}}</ref> With the discovery of [[nuclear fission]] in late 1938, and the need for a [[neutron moderator]] that captured few neutrons, heavy water became a component of early [[Nuclear power|nuclear energy]] research. Since then, heavy water has been an essential component in some types of reactors, both those that generate power and those designed to produce isotopes for nuclear weapons. These [[Pressurized heavy-water reactor|heavy water reactors]] have the advantage of being able to run on natural [[uranium]] without using [[graphite]] moderators that pose radiological<ref>{{cite web|url=http://www-pub.iaea.org/MTCD/publications/PDF/ngwm-cd/PDF-Files/paper%2017%20(Holt).pdf |title=Radioactive Graphite Management at UK Magnox Nuclear Power Stations |website=Pub-iaea.org |access-date=11 January 2017}}</ref> and [[dust explosion]]<ref>{{cite web |url=http://cigr.ageng2012.org/images/fotosg/tabla_137_C0371.pdf |title=Archived copy |access-date=25 August 2012 |url-status=dead |archive-url=https://web.archive.org/web/20140422132744/http://cigr.ageng2012.org/images/fotosg/tabla_137_C0371.pdf |archive-date=22 April 2014 }}</ref> hazards in the decommissioning phase. The graphite moderated Soviet [[RBMK]] design tried to avoid using either [[enriched uranium]] or heavy water (being cooled with ordinary water instead) which produced the positive [[void coefficient]] that was one of a series of flaws in reactor design leading to the [[Chernobyl disaster]]. Most modern reactors use enriched uranium with ordinary water as the moderator.

==Other heavy forms of water==
===Semiheavy water===
[[File:Semiheavy water.svg|thumb|right|120px|Structure of semiheavy water]]
[[Semiheavy water]], HDO, exists whenever there is water with light hydrogen (protium, {{chem|1|H}}) and deuterium (D or {{chem|2|H}}) in the mix. This is because hydrogen atoms ({{sup|1}}H and {{sup|2}}H) are rapidly exchanged between water molecules. Water containing 50% {{chem|1|H}} and 50% {{chem|2|H}} in its hydrogen, is actually about 50% HDO and 25% each of {{chem|H|2|O}} and {{chem|D|2|O}}, in [[dynamic equilibrium]].
In normal water, about 1 molecule in 3,200 is HDO (one hydrogen in 6,400 is {{chem|2|H}}), and heavy water molecules ({{chem|D|2|O}}) only occur in a proportion of about 1 molecule in 41 million (i.e. one in 6,400{{sup|2}}){{Citation needed|reason=the statistical reasoning here is very clear to me. There are three different numbers thrown around, 1/6400,1/20mil,1/41mill. Their statistics aren't cited and their logic isn't foolproof, as can be seen by the fact I'm complaining about it.|date=August 2023}}. Thus semiheavy water molecules are far more common than "pure" (homoisotopic) heavy water molecules.

===Heavy-oxygen water===
Water enriched in the heavier oxygen isotopes [[oxygen-17|{{chem|17|O}}]] and [[oxygen-18|{{chem|18|O}}]] is also commercially available. It is "heavy water" as it is denser than normal water ({{chem|H|2}}{{chem|18|O}} is approximately as dense as {{chem|D|2|O}}, {{chem|H|2}}{{chem|17|O}} is about halfway between {{chem|H|2|O}} and {{chem|D|2|O}})—but is rarely called heavy water, since it does not contain the excess deuterium that gives D{{sub|2}}O its unusual nuclear and biological properties. It is more expensive than D{{sub|2}}O due to the more difficult separation of {{sup|17}}O and {{sup|18}}O.<ref>Mosin, O. V, Ignatov, I. (2011) Separation of Heavy Isotopes Deuterium (D) and Tritium (T) and Oxygen ({{sup|18}}O) in Water Treatment, Clean Water: Problems and Decisions, No. 3–4, pp. 69–78.</ref> H{{sub|2}}{{sup|18}}O is also used for production of [[fluorine-18]] in [[radiopharmaceutical]]s and [[radiotracer]]s, and [[positron emission tomography]]. Small amounts of {{chem|17|O}} and {{chem|18|O}} are naturally present in water, and most processes enriching heavy water also enrich heavier isotopes of oxygen as a side-effect. This is undesirable if the heavy water is to be used as a neutron moderator in nuclear reactors, as {{chem|17|O}} can undergo neutron capture, followed by emission of an [[alpha particle]], producing radioactive {{chem|14|C}}. However, [[doubly labeled water]], containing both a heavy oxygen and hydrogen, is useful as a non-radioactive isotopic tracer.

Compared to the isotopic change of hydrogen atoms, the isotopic change of oxygen has a smaller effect on the physical properties.<ref>Steckel, F., & Szapiro, S. (1963). Physical properties of heavy oxygen water. Part 1.—Density and thermal expansion. Transactions of the Faraday Society, 59, 331-343.</ref>

===Tritiated water===
[[Tritiated water]] contains [[tritium]] ({{sup|3}}H) in place of protium ({{sup|1}}H) or deuterium ({{sup|2}}H). Since tritium is radioactive, tritiated water is also radioactive.

==Physical properties==
{| class="wikitable"
|+Physical properties of isotopologues of water<ref>{{cite web|url=http://www1.lsbu.ac.uk/water/water_properties.html |archiveurl=https://web.archive.org/web/20141007210436/http://www.lsbu.ac.uk/water/water_properties.html |archivedate=7 October 2014 |title=Water Properties (including isotopologues) |website=lsbu.ac.uk |author= Martin Chaplin |access-date=4 December 2017}}</ref>
|-
! Property 
!T{{sub|2}}O (Tritiated water)|| D{{sub|2}}O (Heavy water) || HDO (Semiheavy water) || H{{sub|2}}O (Light water)
|-
| [[Melting point]] ([[Standard atmosphere (unit)|standard pressure]]) 
|{{convert|4.49|C|F K}}|| style="text-align:center;" | {{convert|3.82|C|F K}} || style="text-align:center;"| {{convert|2.04|C|F K}} || style="text-align:center;"| {{convert|0.0|C|F K}}
|-
| [[Boiling point]] 
|{{convert|101.5|C|F K}}|| style="text-align:center;" | {{convert|101.4|C|F K}} || style="text-align:center;"| {{convert|100.7|C|F K}} || style="text-align:center;"| {{convert|100.0|C|F K}}
|-
| [[Density]] at [[Standard temperature and pressure|STP]] (g/[[millilitre|mL]]) 
|1.2133|| style="text-align:center;" | 1.1056 || style="text-align:center;"| 1.054 || style="text-align:center;"| 0.9982
|-
| Temp. of maximum density 
|13.4&nbsp;°C|| style="text-align:center;" | 11.6&nbsp;°C || style="text-align:center;"|Unverified|| style="text-align:center;" | 3.98&nbsp;°C<ref>{{cite book |title=Chemistry and Chemical Reactivity, Volume 1 |edition=7th |first1=John |last1=Kotz |first2=Paul |last2=Teichel |first3=John |last3=Townsend |publisher=Cengage Learning |date=2008 |isbn=978-0-495-38711-4 |page=15 |url=https://books.google.com/books?id=a9emw3FvCrAC}} [https://books.google.com/books?id=a9emw3FvCrAC&pg=PT43 Extract of page 15]</ref>
|-
| [[Dynamic viscosity]] (at 20&nbsp;°C, [[millipascal|mPa]]·[[second|s]]) 
|1.40 (estimated)|| style="text-align:center;" | 1.2467 || style="text-align:center;"| 1.1248 || style="text-align:center;"| 1.0016
|-
| [[Surface tension]] (at 25&nbsp;°C, [[Newton (unit)|N]]/[[Metre|m]])<!--- 1 dyn-cm = 0.1 μJ = 100 nJ ---> 
|Unverified|| style="text-align:center;" | 0.07187 || style="text-align:center;"| 0.07193 || style="text-align:center;"| 0.07198
|-
| [[Heat of fusion]] ([[joule|kJ]]/[[mole (unit)|mol]]) 
|Unverified|| style="text-align:center;" | 6.132 || style="text-align:center;"| 6.227 || style="text-align:center;"| 6.00678
|-
| [[Enthalpy of vaporization|Heat of vaporisation]] (kJ/mol) 
|Unverified|| style="text-align:center;" | 41.521 || style="text-align:center;"|Unverified
| style="text-align:center;" | 40.657
|-
| [[pH]] (at 25&nbsp;°C)<ref name="discussion of pD">[http://www.nuceng.ca/candu/pdf/15%20-%20Chemistry%20in%20CANDU%20Process%20Systems.pdf discussion of pD],</ref> 
|Unverified|| style="text-align:center;" | 7.44 ("pD") || style="text-align:center;"| 7.266 ("pHD") || style="text-align:center;"| 7.0
|-
| [[Base dissociation constant|p''K''<sub>b</sub>]] (at 25&nbsp;°C)<ref name="discussion of pD"/> 
|Unverified|| style="text-align:center;" | 7.44 ("p''K''<sub>b</sub> D<sub>2</sub>O") || style="text-align:center;"|Unverified|| style="text-align:center;" | 7.0
|-
| [[Refractive index]] (at 20&nbsp;°C, 0.5893 [[micrometre|μm]])<ref>{{cite web |url=http://refractiveindex.info/?group=LIQUIDS&material=Heavy_water|title=RefractiveIndex.INFO |access-date=21 January 2010}}</ref> 
|Unverified|| style="text-align:center;" | 1.32844 || style="text-align:center;"|Unverified || style="text-align:center;" |1.33335
|}
The physical properties of water and heavy water differ in several respects. Heavy water is less dissociated than light water at given temperature, and the true concentration of D{{sup|+}} ions is less than {{H+}} ions would be for light water at the same temperature. The same is true of OD{{sup|−}} vs. {{OH-}} ions. For heavy water Kw D{{sub|2}}O (25.0&nbsp;°C) = 1.35 × 10{{sup|−15}}, and [D{{sup|+}}{{hsp}}] must equal [OD{{sup|−}}{{hsp}}] for neutral water. Thus pKw D{{sub|2}}O = p[OD{{sup|−}}] + p[D{{sup|+}}] = 7.44 + 7.44 = 14.87 (25.0&nbsp;°C), and the p[D{{sup|+}}] of neutral heavy water at 25.0&nbsp;°C is 7.44.

The pD of heavy water is generally measured using pH electrodes giving a pH (apparent) value, or pHa, and at various temperatures a true acidic pD can be estimated from the directly pH meter measured pHa, such that pD+ = pHa (apparent reading from pH meter) + 0.41. The electrode correction for alkaline conditions is 0.456 for heavy water. The alkaline correction is then pD+ = pH{{sub|a}}(apparent reading from pH meter) + 0.456. These corrections are slightly different from the differences in p[D+] and p[OD-] of 0.44 from the corresponding ones in heavy water.<ref>[http://www.nuceng.ca/candu/pdf/15%20-%20Chemistry%20in%20CANDU%20Process%20Systems.pdf discussion of pD+],</ref>

Heavy water is 10.6% denser than ordinary water, and heavy water's physically different properties can be seen without equipment if a frozen sample is dropped into normal water, as it will sink. If the water is ice-cold the higher melting temperature of heavy ice can also be observed: it melts at 3.7&nbsp;°C, and thus does not melt in ice-cold normal water.<ref>{{cite magazine |url=http://www.popsci.com/popsci/how20/a07160a72252c010vgnvcm1000004eecbccdrcrd.html |title=How 2.0 |access-date=21 January 2008 |last=Gray |first=Theodore |date=2007 |magazine=Popular Science |url-status=dead |archive-url=https://web.archive.org/web/20071216010940/http://www.popsci.com/popsci/how20/a07160a72252c010vgnvcm1000004eecbccdrcrd.html |archive-date=16 December 2007 }}</ref>

A 1935 experiment reported not the "slightest difference" in taste between ordinary and heavy water.<ref>{{cite journal|doi=10.1126/science.81.2098.273-a  |date=15 March 1935 |volume=81 |issue= 2098|journal=Science |page=273|bibcode = 1935Sci....81..273U |pmid=17811065 | last1 = Urey | first1 = HC |title=Concerning the Taste of Heavy Water | last2 = Failla | first2 = G}}</ref> However, a more recent study confirmed anecdotal observation that heavy water tastes slightly sweet to humans, with the effect mediated by the [[TAS1R2]]/[[TAS1R3]] taste receptor.<ref>{{cite journal|doi=10.1038/s42003-021-01964-y |date=6 April 2021 |volume=4 |issue=1 |journal=Communications Biology |first1=Natalie| last1=Ben Abu| first2=Philip E.| last2=Mason |title=Sweet taste of heavy water|page=440 |pmid=33824405 |pmc=8024362 |doi-access=free }}</ref> Rats given a choice between distilled normal water and heavy water were able to avoid the heavy water based on smell, and it may have a different taste.<ref>{{cite journal|doi=10.1016/0031-9384(79)90124-0 |pmid= 515218 |title= Taste responses to deuterium oxide | volume=23 |issue= 1 |journal=Physiology |pages=69–74 |year=1979 | last1 = Miller | first1 = Inglis J. | last2 = Mooser | first2 = Gregory|s2cid= 39474797 }}</ref> Some people report that minerals in water affect taste, e.g. potassium lending a sweet taste to hard water, but there are many factors of a perceived taste in water besides mineral contents.<ref>{{cite web | title=Is there really a north-south water taste divide? |url=https://www.bbc.com/news/magazine-22247668 | date=29 April 2013 | access-date=12 October 2020 |last=Westcott | first=Kathryn | publisher=BBC News Magazine}}</ref>

Heavy water lacks the [[Color of water|characteristic blue color]] of light water; this is because the [[molecular vibration]] harmonics, which in light water cause weak absorption in the red part of the visible spectrum, are shifted into the [[infrared]] and thus heavy water does not absorb red light.<ref name="Webexhibits">{{cite web |url=http://www.webexhibits.org/causesofcolour/5B.html |title=Colours from Vibration |author=WebExhibits |work=Causes of Colour |publisher=[[WebExhibits]] |url-status=live |archive-url=https://web.archive.org/web/20170223212434/http://www.webexhibits.org/causesofcolour/5B.html |archive-date=23 February 2017 |access-date=21 October 2017 |quote=Heavy water is colourless because all of its corresponding vibrational transitions are shifted to lower energy (higher wavelength) by the increase in isotope mass. }}</ref>

No physical properties are listed for "pure" semi-heavy water because it is unstable as a bulk liquid. In the liquid state, a few water molecules are always in an [[Self-ionization of water|ionized state]], which means the hydrogen atoms can exchange among different oxygen atoms. Semi-heavy water could, in theory, be created via a chemical method,{{explain|date=June 2021}} but it would rapidly transform into a dynamic mixture of 25% light water, 25% heavy water, and 50% semi-heavy. However, if it were made in the gas phase and directly [[Deposition (phase transition)|deposited]] into a solid, semi-heavy water in the form of ice could be stable. This is due to collisions between water vapor molecules being almost completely negligible in the gas phase at standard temperatures, and once crystallized, collisions between the molecules cease altogether due to the rigid lattice structure of solid ice.{{citation needed|date=February 2017}}

==History==
The US scientist and [[Nobel laureate]] [[Harold Urey]] discovered the isotope [[deuterium]] in 1931 and was later able to concentrate it in water.<ref>{{cite journal
 |author1=H. C. Urey |author2=Ferdinand G. Brickwedde |author3=G. M. Murphy | title = A Hydrogen Isotope of Mass 2
 | journal = Physical Review
 | date = 1932
 | volume = 39
 | pages = 164–165
 | doi = 10.1103/PhysRev.39.164
 |bibcode = 1932PhRv...39..164U
 | issue=1| doi-access = free
 }}</ref> Urey's mentor [[Gilbert Newton Lewis]] isolated the first sample of pure heavy water by [[electrolysis]] in 1933.<ref>{{Cite journal| page = 341| year = 1933 | doi = 10.1063/1.1749300| last2 =  MacDonald| first1 = G. N.| volume = 1| last1 = Lewis| journal = The Journal of Chemical Physics | first2 = R. T.| title = Concentration of H2 Isotope| issue = 6|bibcode = 1933JChPh...1..341L }}</ref> [[George de Hevesy]] and Erich Hofer used heavy water in 1934 in one of the first biological tracer experiments, to estimate the rate of turnover of water in the human body.<ref>{{cite journal |first1= George de |last1= Hevesy |first2= Erich |last2= Hofer |journal= Nature |volume= 134 |issue= 3397 |page= 879 |year= 1934 |doi= 10.1038/134879a0 |title= Elimination of Water from the Human Body |bibcode= 1934Natur.134..879H |s2cid= 4108710 }}</ref> The history of large-quantity production and use of heavy water, in early nuclear experiments, is described below.<ref>
{{cite arXiv
 | title =An Early History of Heavy Water
 | author =Chris Waltham
 | date = 20 June 2002
| eprint =physics/0206076
}}</ref>

[[Emilian Bratu]] and [[Otto Redlich]] studied the autodissociation of heavy water in 1934.<ref>Em. Bratu, E. Abel, O. Redlich, Die elektrolytische Dissoziation des schweren Wassers; vorläufige Mitttelung, Zeitschrift für physikalische Chemie, 170, 153 (1934)</ref>

In the 1930s, it was suspected by the United States and Soviet Union that Austrian chemist [[Fritz Johann Hansgirg]] built a pilot plant for the [[Empire of Japan]] in [[Korea under Japanese rule|Japanese ruled northern Korea]] to produce heavy water by using a new process he had invented.<ref name=FH>{{Cite report |url=https://www.academia.edu/7850196 |title=1945: When Korea Faced Its Post-Colonial Future |last=Streifer |first=Bill |publisher=[[Academia.edu]] |access-date=24 March 2016}}</ref>

During the second World War, the company Fosfatbolaget in [[Ljungaverk]], Sweden, produced 2,300 liters per year of heavy water. The heavy water was then sold both to Germany and to the Manhattan Project for the price of 1,40 SEK per gram of heavy water.<ref>{{Cite news|url=http://sverigesradio.se/sida/artikel.aspx?programid=110&artikel=6209697|title=Tungt vatten till kärnvapen tillverkades i Ljungaverk - P4 Västernorrland|last=Radio|first=Sveriges|newspaper=Sveriges Radio |date=10 July 2015 |access-date=22 January 2018}}</ref>

In October 1939, [[Soviet]] [[physicists]] [[Yakov Borisovich Zel'dovich]] and  [[Yulii Borisovich Khariton]] concluded that heavy water and carbon were the only feasible moderators for a [[natural uranium]] reactor, and in August 1940, along with [[Georgy Flyorov]], submitted a plan to the [[Russian Academy of Sciences]] calculating that 15 tons of heavy water were needed for a reactor. With the [[Soviet Union]] having no uranium mines at the time, young Academy workers were sent to Leningrad photographic shops to buy uranium nitrate, but the entire heavy water project was halted in 1941 when German forces invaded during [[Operation Barbarossa]].

By 1943, Soviet scientists had discovered that all scientific literature relating to heavy water had disappeared from the West, which Flyorov in a letter warned Soviet leader [[Joseph Stalin]] about,<ref>{{cite web | url=https://www.osti.gov/opennet/manhattan-project-history/Events/1942-1945/espionage.htm | title=Manhattan Project: Espionage and the Manhattan Project, 1940–1945}}</ref> and at which time there was only 2–3&nbsp;kg of heavy water in the entire country. In late 1943, the Soviet purchasing commission in the U.S. obtained 1&nbsp;kg of heavy water and a further 100&nbsp;kg in February 1945, and upon [[World War II]] ending, the [[NKVD]] took over the project.

In October 1946, as part of the [[Russian Alsos]], the [[NKVD]] deported to the [[Soviet Union]] from [[Germany]] the German scientists who had worked on heavy water production during the war, including [[Karl-Hermann Geib]], the inventor of the [[Girdler sulfide process]].<ref name=KG>{{Cite report | url=http://sworld.com.ua/e-journal/j11505.pdf#page=3 | title=Heavywater. History of One Priority. Part 3. | volume=J11505 | issn=2227-6920 | last1=Pietsch | first1=Barbara | last2=Sadovsky | first2=A.S. | publisher=Karpov Institute of Physical Chemistry | date=May 2015 | access-date=21 March 2016 | format=[[PDF]] | via=International periodic scientific journal (SWorld)}}</ref>  These German scientists worked under the supervision of [[Germany|German]] [[physical chemist]]  [[Max Volmer]] at the Institute of Physical Chemistry in [[Moscow]] with the plant they constructed producing large quantities of heavy water by 1948.<ref name=HW/><ref>{{Cite report |url=https://www.nonproliferation.org/wp-content/uploads/npr/72pavel.pdf |title=German Scientists in the Soviet Atomic Project  |last=Oleynikov |first=Pavel V. |publisher=The Nonproliferation Review |date=2000 |access-date=19 March 2016}}</ref>

==Effect on biological systems==
Different isotopes of chemical elements have slightly different chemical behaviors, but for most elements the differences are far too small to have a biological effect. In the case of hydrogen, larger differences in chemical properties among protium, deuterium, and tritium occur because chemical bond energy depends on the [[reduced mass]] of the nucleus–electron system; this is altered in heavy-hydrogen compounds (hydrogen-deuterium oxide is the most common) more than for heavy-isotope substitution involving other chemical elements. The isotope effects are especially relevant in biological systems, which are very sensitive to even the smaller changes, due to isotopically influenced properties of water when it acts as a [[solvent]].

To perform their tasks, [[enzyme]]s rely on their finely tuned networks of [[hydrogen bond]]s, both in the active center with their substrates and outside the active center, to stabilize their [[tertiary structure]]s. As a hydrogen bond with deuterium is slightly stronger<ref>Katz, J. J. (1965). "Chemical and biological studies with deuterium".
39th Annual Priestly Lecture, Pennsylvania State University,
University Park, Pennsylvania. pp. 1–110, August 2008.</ref> than one involving ordinary hydrogen, in a highly deuterated environment, some normal reactions in cells are disrupted.

Particularly hard-hit by heavy water are the delicate assemblies of [[mitotic spindle]] formations necessary for [[mitosis|cell division]] in [[eukaryote]]s. Plants stop growing and seeds do not germinate when given only heavy water, because heavy water stops eukaryotic cell division.<ref>{{cite journal | last1 = Bild | first1 = W. | last2 = Năstasă | first2 = V. | last3 = Haulică | year = 2004 | title = In Vivo and in Vitro Research on the Biological Effects of Deuterium-depleted water: Influence of Deuterium-depleted water on Cultured Cell Growth | journal = Romanian Journal of Physiology | volume = 41 | issue = 1–2| pages = 53–67 | pmid = 15984656 }}</ref> Tobacco does not germinate, but wheat does.<ref>{{Cite journal |last=Urey |first=Harold C. |date=1935 |title=Heavy Water |url=https://www.jstor.org/stable/24999142 |journal=Scientific American |volume=152 |issue=6 |pages=300–302 |doi=10.1038/scientificamerican0635-300 |jstor=24999142 |bibcode=1935SciAm.152..300U |issn=0036-8733}}</ref> The deuterium cell is larger and is a modification of the direction of division.<ref>Crespi, H., Conrad, S., Uphaus, R., Katz, J. (1960). "Cultivation of Microorganisms in Heavy Water". ''Annals of the New York Academy of Sciences, Deuterium Isotopes in Chemistry and Biology'', pp. 648–666.</ref><ref>Mosin, O. V., I. Ignatov, I. (2013). "Microbiological Synthesis of 2H-Labeled Phenylalanine, Alanine, Valine, and Leucine/Isoleucine with Different Degrees of Deuterium Enrichment by the Gram-Positive Facultative Methylotrophic Bacterium Вrevibacterium Methylicum". ''International Journal of Biomedicine'' Vol. 3, N 2, pp. 132–138.</ref> The cell membrane also changes, and it reacts first to the impact of heavy water. In 1972, it was demonstrated that an increase in the percentage of deuterium in water reduces plant growth.<ref>{{cite journal | last1 = Katz | first1 = J. | last2 = Crespy | first2 = H. L. | year = 1972| title = Biologically important isotope hybrid compounds in nmr: 1H Fourier transform nmr at unnatural abundance| doi = 10.1351/pac197232010221 | pmid = 4343107 | journal = Pure and Applied Chemistry | volume = 32 | issue = 1–4| pages = 221–250 | doi-access = free }}</ref> Research conducted on the growth of [[prokaryote]] microorganisms in artificial conditions of a heavy hydrogen environment showed that in this environment, all the hydrogen atoms of water could be replaced with deuterium.<ref>{{cite journal | last1 = Mosin | first1 = O. B. | last2 = Skladnev | first2 = D. A. | last3 = Egorova | first3 = T. A. | last4 = Shvets | first4 = V. I. | year = 1996 | title = Biological Effects of Heavy Water | journal = Bioorganic Chemistry | volume = 22 | issue = 10–11| pages = 861–874 }}</ref><ref>Mosin, O. V., Shvez, V. I, Skladnev, D. A., Ignatov, I. (2012). "Studying of Microbic Synthesis of Deuterium Labeled L-Phenylalanin by Methylotrophic Bacterium Brevibacterium Methylicum on Media with Different Content of Heavy Water". ''Russian Journal of Biopharmaceuticals'', No. 1, Vol. 4, No 1, pp. 11–22.</ref> Experiments showed that bacteria can live in 98% heavy water.<ref>Skladnev D. A., Mosin O. V., Egorova T. A., Eremin S. V., Shvets V. I. (1996). "Methylotrophic Bacteria as Sources of 2H-and 13C-amino Acids". ''Biotechnology'', pp. 14–22.</ref> Concentrations over 50% are lethal to multicellular organisms, but a few exceptions are known: plant species such as switchgrass (''[[Panicum virgatum]]'') which is able to grow on 50% D<sub>2</sub>O;<ref>{{cite journal | last1 = Evans | first1 = B. R. | display-authors = etal | year = 2015 | title = Production of deuterated switchgrass by hydroponic cultivation | journal = Planta | volume = 242 | issue = 1 | pages = 215–222 | doi=10.1007/s00425-015-2298-0 | pmid = 25896375 | bibcode = 2015Plant.242..215E | osti = 1185899 | s2cid = 18477008 }}</ref> ''[[Arabidopsis thaliana]]'' (70% D{{sub|2}}O);<ref>{{cite journal | last1 = Bhatia | first1 = C. R. | display-authors = etal | year = 1968 | title = Adaptation and growth response of ''Arabidopsis thaliana'' to deuterium |journal=Planta | volume=80 | issue = 2 | pages = 176–184 | doi=10.1007/BF00385593 | bibcode = 1968Plant..80..176B | s2cid = 19662801 }}</ref> ''[[Vesicularia dubyana]]'' (85% D<sub>2</sub>O);<ref>{{cite journal | last1 = Kutyshenko | first1 = V. P. | display-authors = etal | year = 2015 | title = 'In-plant' NMR: Analysis of the Intact Plant ''Vesicularia dubyana'' by High Resolution NMR Spectroscopy |journal=Molecules | volume = 20 | issue = 3 | pages = 4359–4368 | doi=10.3390/molecules20034359 | doi-access = free | s2cid = 19662801 }}</ref> ''[[Funaria hygrometrica]]'' (90% D{{sub|2}}O);<ref>{{cite journal | last1 = Vergara | first1 = F. | display-authors = etal | year = 2018 | title = ''Funaria hygrometrica'' Hedw. elevated tolerance to D<sub>2</sub>O: its use for the production of highly deuterated metabolites | journal = Planta | volume = 247 | issue = 2 | pages = 405–412 | doi=10.1007/s00425-017-2794-5 | pmid = 29030693 | bibcode = 2018Plant.247..405V | s2cid = 11302702 }}</ref> and the [[anhydrobiotic]] species of [[nematode]] ''[[Panagrolaimus superbus]]'' (nearly 100% D{{sub|2}}O).<ref name="An animal able to tolerate D">{{cite journal | last1 = de Carli | first1 = G. J. | display-authors = etal | year = 2020 | title = An animal able to tolerate D<sub>2</sub>O | journal = ChemBioChem | volume = 22 | issue = 6 | pages = 988–991 | doi=10.1002/cbic.202000642 | pmid = 33125805 | s2cid = 226218470 }}</ref>

A comprehensive study of heavy water on the fission yeast ''[[Schizosaccharomyces pombe]]'' showed that the cells displayed an altered glucose metabolism and slow growth at high concentrations of heavy water.<ref name="pubs.acs.org">{{Cite journal|last1=Kampmeyer|first1=Caroline|last2=Johansen|first2=Jens V.|last3=Holmberg|first3=Christian|last4=Karlson|first4=Magnus|last5=Gersing|first5=Sarah K.|last6=Bordallo|first6=Heloisa N.|last7=Kragelund|first7=Birthe B.|last8=Lerche|first8=Mathilde H.|last9=Jourdain|first9=Isabelle|last10=Winther|first10=Jakob R.|last11=Hartmann-Petersen|first11=Rasmus|date=17 April 2020|title=Mutations in a Single Signaling Pathway Allow Cell Growth in Heavy Water|url=https://pubs.acs.org/doi/10.1021/acssynbio.9b00376|journal=ACS Synthetic Biology|language=en|volume=9|issue=4|pages=733–748|doi=10.1021/acssynbio.9b00376|pmid=32142608|s2cid=212621576|issn=2161-5063}}</ref> In addition, the cells activated the heat-shock response pathway and the cell integrity pathway, and mutants in the cell integrity pathway displayed increased tolerance to heavy water.<ref name="pubs.acs.org" /> Despite its toxicity at high levels, heavy water has been observed to extend lifespan of certain yeasts by up to 85%, with the hypothesized mechanism being the reduction of reactive oxygen species turnover.<ref>{{cite journal | last1=Li | first1=Xiyan | last2=Snyder | first2=Michael P. | title=Yeast longevity promoted by reversing aging-associated decline in heavy isotope content | journal=npj Aging and Mechanisms of Disease | publisher=Springer Science and Business Media LLC | volume=2 | issue=1 | date=2016-02-18 | pages=16004– | issn=2056-3973 | doi=10.1038/npjamd.2016.4| pmid=28721263 | pmc=5515009 }}</ref>

Heavy water affects the period of [[circadian rhythm|circadian oscillations]], consistently increasing the length of each cycle. The effect has been demonstrated in unicellular organisms, green plants, isopods, insects, birds, mice, and hamsters. The mechanism is unknown.<ref>{{cite journal |title= A Differential Effect of Heavy Water on Temperature-Dependent and Temperature-Compensated Aspects of the Circadian System of Drosophila pseudoobscura |last1=Pittendrigh |first1=C. S. |last2=Caldarola |first2=P. C. |last3=Cosbey |first3=E. S. |journal= [[Proceedings of the National Academy of Sciences USA]] |volume= 70 |issue= 7 |date=July 1973 |pages= 2037–2041 |pmid= 4516204|doi= 10.1073/pnas.70.7.2037 |pmc= 433660 |bibcode = 1973PNAS...70.2037P |doi-access=free }}</ref>

Like ethanol, heavy water temporarily changes the relative density of cupula relative to the endolymph in the vestibular organ, causing [[Positional alcohol nystagmus|positional nystagmus]], illusions of bodily rotations, dizziness, and nausea. However, the direction of nystagmus is in the opposite direction of ethanol, since it is denser than water, not lighter.<ref name=":0">{{Cite journal |last1=Money |first1=K. E. |last2=Myles |first2=W. S. |date=February 1974 |title=Heavy water nystagmus and effects of alcohol |url=https://www.nature.com/articles/247404a0 |journal=Nature |language=en |volume=247 |issue=5440 |pages=404–405 |doi=10.1038/247404a0 |pmid=4544739 |bibcode=1974Natur.247..404M |issn=1476-4687}}</ref>

===Effect on animals===
Experiments with mice, rats, and dogs<ref name="k">{{cite journal |pmid=10535697 |title=Pharmacological uses and perspectives of heavy water and deuterated compounds |first1=D. J. |last1=Kushner |first2=Alison |last2=Baker |first3=T. G. |last3=Dunstall |journal=Canadian Journal of Physiology and Pharmacology |volume=77 |issue=2 |pages=79–88 |date=1999 |quote=...&nbsp;used in boron neutron capture therapy ... D{{sub|2}}O is more toxic to malignant than normal animal cells ... Protozoa are able to withstand up to 70% D{{sub|2}}O. Algae and bacteria can adapt to grow in 100% D{{sub|2}}O | doi = 10.1139/cjpp-77-2-79}}</ref> have shown that a degree of 25% deuteration causes (sometimes irreversible) sterility, because neither [[gamete]]s nor [[zygote]]s can develop. High concentrations of heavy water (90%) rapidly kill fish, [[tadpole]]s, [[flatworm]]s, and ''[[Drosophila]]''. Mice raised from birth with 30% heavy water have 25% deuteration in body fluid and 10% in brains. They are normal except for sterility. Deuteration during pregnancy induces fetal abnormality. Higher deuteration in body fluid causes death.<ref name=":1">{{Cite magazine |last=Katz |first=Joseph J. |date=1960 |title=The Biology of Heavy Water |url=https://www.jstor.org/stable/24940548 |magazine=Scientific American |volume=203 |issue=1 |pages=106–117 |jstor=24940548 |issn=0036-8733}}</ref> Mammals (for example, rats) given heavy water to drink die after a week, at a time when their body water approaches about 50% deuteration.<ref>{{cite journal | last1 = Thomson | first1 = J. F. | year = 1960 | title = Physiological Effects of D{{sub|2}}O in Mammals. Deuterium Isotope Effects in Chemistry and Biology | journal = Annals of the New York Academy of Sciences | volume = 84 | issue = 16| pages = 736–744 | doi=10.1111/j.1749-6632.1960.tb39105.x| pmid = 13776654 |bibcode = 1960NYASA..84..736T | s2cid = 84422613 }}</ref> The mode of death appears to be the same as that in [[cytotoxicity|cytotoxic poisoning]] (such as [[chemotherapy]]) or in acute radiation syndrome (though deuterium is not radioactive), and is caused by deuterium's action in generally inhibiting cell division. It is more toxic to malignant cells than normal cells, but the concentrations needed are too high for regular use.<ref name="k"/> As may occur in chemotherapy, deuterium-poisoned mammals die of a failure of bone marrow (producing bleeding and infections) and of intestinal-barrier functions (producing [[diarrhea]] and [[fluid loss|loss of fluids]]).

Despite the problems of plants and animals in living with too much deuterium, prokaryotic organisms such as bacteria, which do not have the mitotic problems induced by deuterium, may be grown and propagated in fully deuterated conditions, resulting in replacement of all hydrogen atoms in the bacterial proteins and DNA with the deuterium isotope.<ref name="k"/><ref>Trotsenko, Y. A., Khmelenina, V. N., Beschastny, A. P. (1995). "The Ribulose Monophosphate (Quayle) Cycle: News and Views. Microbial Growth on C1 Compounds". Proceedings of the 8th International Symposium on Microbial Growth on C1 Compounds (Lindstrom M.E., Tabita F.R., eds.). San Diego (USA), Boston: Kluwer Academic, pp. 23–26.</ref> This leads to a process of [[bootstrapping]]. With prokaryotes producing fully deuterated glucose, fully deuterated ''[[Escherichia coli]]'' and ''[[Torula]]'' were raised, and they could produce even more complex fully deuterated chemicals. Molds like ''[[Aspergillus]]'' could not replicate under fully deuterated conditions.<ref name=":1" />

In higher organisms, full replacement with heavy isotopes can be accomplished with other non-radioactive heavy isotopes (such as carbon-13, nitrogen-15, and oxygen-18), but this cannot be done for deuterium. This is a consequence of the ratio of nuclear masses between the isotopes of hydrogen, which is much greater than for any other element.<ref name="isotopegeochem">{{cite book|last=Hoefs|first=J.|year=1997|publisher=Springer|title=Stable Isotope Geochemistry|isbn=978-3-540-61126-4|edition=4}}</ref>

Deuterium oxide is used to enhance [[boron neutron capture therapy]], but this effect does not rely on the biological or chemical effects of deuterium, but instead on deuterium's ability to moderate (slow) neutrons without capturing them.<ref name="k" /> 2021 experimental evidence indicates that systemic administration of deuterium oxide (30% drinking water supplementation) suppresses [[tumor]] growth in a standard mouse model of human [[melanoma]], an effect attributed to selective induction of cellular stress signaling and gene expression in tumor cells.<ref>{{cite journal |title= Deuterium Oxide (D2O) Induces Early Stress Response Gene Expression and Impairs Growth and Metastasis of Experimental Malignant Melanoma |last1=Jandova |first1=J. |last2=Hua |first2=A. B. |last3=Fimbres |first3=J. |last4=Wondrak |first4=G. T. |journal= [[Cancers (journal)|Cancers]] |volume= 13 |issue= 4 |date=February 2021 |pages= 605 |pmid= 33546433|doi= 10.3390/cancers13040605  |pmc= 7913703 |doi-access=free }}</ref>

===Toxicity in humans===
Because it would take a very large amount of heavy water to replace 25% to 50% of a human being's body water (water being in turn 50–75% of body weight<ref>{{cite journal | last1 = Watson | first1 = P. E. | display-authors = etal | year = 1980 | title = Total body water volumes for adult males and females estimated from simple anthropometric measurements | journal = The American Journal of Clinical Nutrition | volume = 33 | issue = 1| pages = 27–39 | pmid = 6986753 | doi = 10.1093/ajcn/33.1.27 | s2cid = 4442439 | doi-access = free }}</ref>) with heavy water, accidental or intentional [[poison]]ing with heavy water is unlikely to the point of practical disregard. Poisoning would require that the victim ingest large amounts of heavy water without significant normal water intake for many days to produce any noticeable toxic effects.

Oral doses of heavy water in the range of several grams, as well as [[Oxygen-18|heavy oxygen]] {{sup|18}}O, are routinely used in human metabolic experiments. (See [[doubly labeled water]] testing.) Since one in about every 6,400 hydrogen atoms is deuterium, a {{convert|50|kg|adj=on}} human containing {{convert|32|kg}} of body water would normally contain enough deuterium (about {{convert|1.1|g|disp=or}}) to make {{convert|5.5|g}} of pure heavy water, so roughly this dose is required to double the amount of deuterium in the body.<!--- atomic mass of water, taking into account the three isotopes of hydrogen and the three of oxygen, is 18.01527; 32 kg of water is thus 1776.27 mol. Figuring in the abundances, we get 1.114014 g of deuterium (0.553258 mol); if we mix this with half as many moles of mean oxygen (0.138359 mol × 15.99930457 mol/g), we get 5.54 g of D<sub>2</sub>O --->

A loss of blood pressure may partially explain the reported incidence of dizziness upon ingestion of heavy water. However, it is more likely that this symptom can be attributed to altered [[vestibular system|vestibular function]]. Heavy water, like ethanol, causes a temporary difference in the density of endolymph within the cupula, which confuses the [[Vestibulo–ocular reflex#Nystagmus|vestibulo–ocular reflex]] and causes motion sickness symptoms.<ref>{{cite journal|last1=Money|first1=K. E.|last2=Myles|first2=W. S.|title=Heavy water nystagmus and effects of alcohol|journal=Nature|date=February 1974|volume=247|pages=404–405|doi=10.1038/247404a0|pmid=4544739|bibcode = 1974Natur.247..404M|issue=5440 |s2cid=4166559}}</ref>

===Heavy water radiation contamination confusion===
Although many people associate heavy water primarily with its use in nuclear reactors, pure heavy water is not radioactive. Commercial-grade heavy water is slightly radioactive due to the presence of minute traces of natural tritium, but the same is true of ordinary water. Heavy water that has been used as a coolant in nuclear power plants contains substantially more tritium as a result of neutron bombardment of the deuterium in the heavy water ([[Tritium#Health risks|tritium is a health risk]] when ingested in large quantities).

In 1990, a disgruntled employee at the [[Point Lepreau Nuclear Generating Station]] in Canada obtained a sample (estimated as about a "half cup") of heavy water from the primary heat transport loop of the [[nuclear reactor]], and loaded it into a cafeteria drink dispenser. Eight employees drank some of the contaminated water. The incident was discovered when employees began leaving [[bioassay]] urine samples with elevated [[tritium]] levels. The quantity of heavy water involved was far below levels that could induce heavy water toxicity, but several employees received elevated radiation doses from tritium and neutron-activated chemicals in the water.<ref>{{cite web |url=http://www.ecology.at/nni/site.php?site=Point++Lepreau |title=Point Lepreau in Canada |publisher=NNI (No Nukes Inforesource) |access-date=10 September 2007 |archive-url = https://web.archive.org/web/20070710224724/http://www.ecology.at/nni/site.php?site=Point++Lepreau <!-- Bot retrieved archive --> |archive-date = 10 July 2007}}</ref> This was not an incident of heavy water poisoning, but rather radiation poisoning from other isotopes in the heavy water.

Some news services were not careful to distinguish these points, and some of the public were left with the impression that heavy water is normally radioactive and more severely toxic than it actually is. Even if pure heavy water had been used in the water cooler indefinitely, it is not likely the incident would have been detected or caused harm, since no employee would be expected to get much more than 25% of their daily drinking water from such a source.<ref>
{{cite news |date=6 March 1990 |title=Radiation Punch Nuke Plant Worker Charged With Spiking Juice |newspaper=[[Philadelphia Daily News]] |agency=Associated Press |url=http://nl.newsbank.com/nl-search/we/Archives?p_product=DN&s_site=philly&p_multi=PI%7CDN&p_theme=realcities&p_action=search&p_maxdocs=200&p_topdoc=1&p_text_direct-0=0EB29D29C1FD71F6&p_field_direct-0=document_id&p_perpage=10&p_sort=YMD_date:D&s_trackval=GooglePM |url-status=dead |access-date=30 November 2006 |archive-url=https://web.archive.org/web/20121024214618/http://nl.newsbank.com/nl-search/we/Archives?p_product=DN&s_site=philly&p_multi=PI%7CDN&p_theme=realcities&p_action=search&p_maxdocs=200&p_topdoc=1&p_text_direct-0=0EB29D29C1FD71F6&p_field_direct-0=document_id&p_perpage=10&p_sort=YMD_date:D&s_trackval=GooglePM |archive-date=24 October 2012}}
</ref>

==Production methods==
The most cost-effective process for producing heavy water is the dual temperature exchange sulfide process (known as the [[Girdler sulfide process]]) developed in parallel by [[Karl-Hermann Geib]] and [[Jerome S. Spevack]] in 1943.<ref name="HW">{{Cite report |title=An Early History of Heavy Water |last=Waltham |first=Chris |publisher=[[University of British Columbia]] |date=August 1998 |arxiv=physics/0206076 }}</ref> An alternative process,<ref>{{cite web|url=https://patents.google.com/patent/US4620909 |title=Method for isotope replenishment in an exchange liquid used in a laser |access-date=14 August 2010}}</ref> patented by Graham M. Keyser, uses [[lasers]] to selectively dissociate deuterated [[hydrofluorocarbons]] to form deuterium [[fluoride]], which can then be separated by physical means. Although the energy consumption for this process is much less than for the Girdler sulfide process, this method is currently uneconomical due to the expense of procuring the necessary hydrofluorocarbons.

As noted, modern commercial heavy water is almost universally referred to, and sold as, deuterium oxide. It is most often sold in various grades of purity, from 98% enrichment to 99.75–99.98% deuterium enrichment (nuclear reactor grade) and occasionally even higher isotopic purity.

==Production by country==
===Argentina===
[[Argentina]] was the main producer of heavy water, using an ammonia/hydrogen exchange based plant supplied by Switzerland's [[Sulzer (manufacturer)|Sulzer]] company. It was also a major exporter to Canada, Germany, the US and other countries. The heavy water production facility located in [[Arroyito, Neuquén|Arroyito]] was the world's largest heavy water production facility. Argentina produced {{convert|200|ST|t|abbr=off}} of heavy water per year in 2015 using the ''monothermal ammonia-hydrogen isotopic exchange'' method.<ref>{{cite web |url=http://www.trimodbesta.com/ru/references/references-plant-engineering.html?getFile=ApplicationInformation_BAG_201510/500_plant/AI_BAG_Arroyito_HeavyWater_LTG501EN1510_English_.pdf |title=Trimod Besta : Arroyito Heavy Water Production Plant, Argentina |website=Trimodbesta.com |access-date=11 January 2017 |archive-date=6 October 2016 |archive-url=https://web.archive.org/web/20161006084020/http://www.trimodbesta.com/ru/references/references-plant-engineering.html?getFile=ApplicationInformation_BAG_201510/500_plant/AI_BAG_Arroyito_HeavyWater_LTG501EN1510_English_.pdf |url-status=dead }}</ref><ref>{{Cite journal|author=Ecabert, R. |url=https://inis.iaea.org/search/search.aspx?orig_q=RN:16017940 |title=The heavy water production plant at Arroyito, Arge..&#124;INIS |issue=3 |pages=21–24 |journal=Sulzer Technical Review |volume=66 |access-date=11 January 2017|year=1984 }}</ref><ref>{{Cite journal|author=Garcia, E.E. |url=https://inis.iaea.org/search/search.aspx?orig_q=RN:16038740 |title=The projects for heavy water production of the Arg..&#124;INIS |pages=50–64 |journal=Energia Nuclear (Buenos Aires) |access-date=11 January 2017|year=1982 }}</ref><ref>{{Cite journal|author=Conde Bidabehere, Luis F. |url=https://inis.iaea.org/search/search.aspx?orig_q=RN:33064784 |title=Heavy water. An original project in the Argentine ..&#124;INIS |website=Inis.iaea.org |access-date=11 January 2017|year=2000 }}</ref><ref>{{cite web|url=http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/18/096/18096007.pdf#page=441 |format=PDF |title=Selection of a Safeguards Approach for the Arroyito Heavy Water Production Plant |website=Iaea.org |access-date=11 January 2017}}</ref> Since 2017, the Arroyito plant has not been operational.<ref>{{cite web|url=https://eleconomista.com.ar/actualidad/argentina-recupera-planta-industrial-agua-pesada-n54887 |title=Argentina recupera la Planta Industrial de Agua Pesada |access-date=29 December 2022}}</ref>

===United States===
During the [[Manhattan Project]] the United States constructed three heavy water production plants as part of the [[P-9 Project]] at Morgantown Ordnance Works, near [[Morgantown, West Virginia]]; at the Wabash River Ordnance Works, near Dana and [[Newport, Indiana]]; and at the Alabama Ordnance Works, near [[Childersburg, Alabama|Childersburg]] and [[Sylacauga, Alabama]]. Heavy water was also acquired from the Cominco plant in [[Trail, British Columbia]], Canada. The [[Chicago Pile-3]] experimental reactor used heavy water as a moderator and went critical in 1944.<ref>{{Cite arXiv |last=Waltham |first=Chris |date=October 2011 |title=An Early History of Heavy Water |pages=8–9|eprint=physics/0206076 }}</ref> The three domestic production plants were shut down in 1945 after producing around {{cvt|81,470|lb|kg}} of product.<ref>{{Cite book |title=Manhattan District History Book III The P-9 Project |language=English}}</ref> The Wabash plant resumed heavy water production in 1952.

In 1953, the United States began using heavy water in [[plutonium]] production reactors at the [[Savannah River Site]]. The first of the five [[Pressurized heavy-water reactor|heavy water reactors]] came online in 1953, and the last was placed in cold shutdown in 1996. The reactors were heavy water reactors so that they could produce both plutonium and tritium for the US nuclear weapons program.

The U.S. developed the [[Girdler sulfide process|Girdler sulfide]] chemical exchange production process—which was first demonstrated on a large scale at the [[Dana, Indiana]] plant in 1945 and at the Savannah River Site in 1952.

===India===
India is the world's largest producer of heavy water through its [[Heavy Water Board]].<ref>{{Cite web |title=Nuclear Applications {{!}} Heavy Water Board, Government of India |url=https://www.hwb.gov.in/nuclear-applications |access-date=25 March 2022 |website=www.hwb.gov.in}}</ref> It exports heavy water to countries including the Republic of Korea, China, and the United States.<ref>{{cite news |last1=Laxman |first1=Srinivas |title=Full circle: India exports heavy water to US |url=https://timesofindia.indiatimes.com/india/full-circle-india-exports-heavy-water-to-us/articleshow/1774012.cms |access-date=21 July 2022 |work=The Times of India}}</ref><ref>{{cite news |last1=PTI |first1= |title=Heavy Water Board reaches new high in export market |url=https://www.livemint.com/Home-Page/iQNmfgnbS9FMtBH3l5IzSL/Heavy-Water-Board-reaches-new-high-in-export-market.html |access-date=21 July 2022 |agency=Livemint |date=18 March 2007}}</ref><!-- Development of heavy water process in India happened in three phases. The first phase (late 1950s to mid-1980s) was a period of technology development, the second phase included deployment of the technology and process stabilisation (mid-1980s to early 1990s), and third phase saw consolidation and a shift towards improvement in production and energy conservation.{{citation needed|date=October 2020}}-->

===Norway===
{{Main|Norwegian heavy water sabotage}}
[[File:Deuterium oxide Norsk.jpg|thumb|"Heavy water" made by Norsk Hydro]]
In 1934, [[Norsk Hydro]] built the first commercial heavy water plant at [[Vemork]], [[Tinn]], eventually producing {{convert|4|kg|lb}} per day.<ref>{{cite web|url=http://www.ntnu.no/forskning/kjentealumni/tronstad|title=Leif Tronstad|publisher=Norwegian University of Science and Technology|accessdate=8 March 2021|archive-date=7 February 2012|archive-url=https://web.archive.org/web/20120207150639/http://www.ntnu.no/forskning/kjentealumni/tronstad|url-status=dead}}</ref> From 1940 and throughout [[World War II]], the plant was under [[Nazi Germany|German]] control, and the [[Allies of World War II|Allies]] decided to destroy the plant and its heavy water to inhibit German development of nuclear weapons. In late 1942, a planned raid called [[Operation Freshman]] by British airborne troops failed, both gliders crashing. The raiders were killed in the crash or subsequently executed by the Germans.

On the night of 27 February 1943 [[Operation Gunnerside]] succeeded. Norwegian commandos and local resistance managed to demolish small, but key parts of the electrolytic cells, dumping the accumulated heavy water down the factory drains.<ref>{{cite book|last=Gallagher|first=Thomas|title=Assault In Norway: Sabotaging the Nazi Nuclear Program|publisher=The Lyons Press|year=2002|location=Guilford, Connecticut|isbn=978-1585747504}}</ref>

On 16 November 1943, the Allied air forces dropped more than 400 bombs on the site. The Allied air raid prompted the Nazi government to move all available heavy water to Germany for safekeeping. On 20 February 1944, a Norwegian partisan sank the ferry [[SF Hydro|M/F&nbsp;''Hydro'']] carrying heavy water across [[Lake Tinn]], at the cost of 14 Norwegian civilian lives, and most of the heavy water was presumably lost. A few of the barrels were only half full, hence buoyant, and may have been salvaged and transported to Germany.

Recent investigation of production records at Norsk Hydro and analysis of an intact barrel that was salvaged in 2004<!--reference: documentary on PBS/Discovery Channel--> revealed that although the barrels in this shipment contained water of [[pH]]&nbsp;14—indicative of the alkaline electrolytic refinement process—they did not contain high concentrations of D{{sub|2}}O.<ref name=NOVA>{{cite web |url=https://www.pbs.org/wgbh/nova/transcripts/3216_hydro.html |title=Hitler's Sunken Secret (transcript) |publisher=NOVA Web site |date=8 November 2005 |access-date=8 October 2008 |author=NOVA|author-link=Nova (American TV program) }}</ref> Despite the apparent size of the shipment, the total quantity of pure heavy water was quite small, most barrels only containing 0.5–1% pure heavy water. The Germans would have needed about 5 tons of heavy water to get a nuclear reactor running.<!--reference: documentary on Nova / Hitler's Sunken Treasure--> The manifest clearly indicated that there was only half a ton of heavy water being transported to Germany. ''Hydro'' was carrying far too little heavy water for one reactor, let alone the 10 or more tons needed to make enough plutonium for a nuclear weapon.<ref name="NOVA"/> The [[German nuclear weapons program]] was much less advanced than the Manhattan Project, and no reactor constructed in Nazi Germany came close to reaching [[criticality (status)|criticality]]. No amount of heavy water would have changed that.

Israel admitted running the [[Negev Nuclear Research Center|Dimona reactor]] with Norwegian heavy water sold to it in 1959. Through re-export using Romania and Germany, India probably also used Norwegian heavy water.<ref>[http://www.wisconsinproject.org/pubs/editorials/1988/3scandals.htm "3 Scandals Oslo Must Put to Rest"] {{webarchive|url=https://web.archive.org/web/20120423220548/http://www.wisconsinproject.org/pubs/editorials/1988/3scandals.htm |date=23 April 2012 }}. ''[[International Herald Tribune]]'', 1988-10-07, p. 6 (14 September 1988). Retrieved from Wisconsinproject.org on 20 April 2012.</ref><ref name="Milhollin1987">{{cite journal|last1=Milhollin|first1=Gary|title=Heavy Water Cheaters|journal=Foreign Policy|issue=69|pages=100–119|year=1987|issn=0015-7228|doi=10.2307/1148590|jstor=1148590}}</ref>

===Canada===
As part of its contribution to the Manhattan Project, Canada built and operated a {{convert|1000|to|1200|lb|kg}} per month (design capacity) electrolytic heavy water plant at [[Trail, British Columbia]], which started operation in 1943.<ref>{{cite report 
| title = Manhattan District History, Book III, The P-9 Project
| url = https://www.osti.gov/includes/opennet/includes/MED_scans/Book%20III%20-%20The%20P-9%20Project.pdf
| date = 8 April 1947
| publisher = [[United States Department of Energy]]
| page = 99
| access-date = 16 February 2019}} The original design production was 1000 lbs./month, later increased to 1200 lbs./month. Maximum production was 1330 lbs./month.
</ref>

The [[Atomic Energy of Canada Limited]] (AECL) design of power reactor requires large quantities of heavy water to act as a [[neutron moderator]] and coolant. AECL ordered two heavy water plants, which were built and operated in [[Atlantic Canada]] at [[Glace Bay]], [[Nova Scotia]] (by Deuterium of Canada Limited) and [[Point Tupper, Richmond County]], Nova Scotia (by Canadian General Electric). These plants proved to have significant design, construction and production problems. The Glace Bay plant reached full production in 1984 after being taken over by AECL in 1971.<ref>{{cite book |last1=MacInnis |first1=Roland |title=Hell And Heavy Water |date=2018 |publisher=Roland MacInnis |isbn=978-1720808770 |pages=38, 54 |edition=1}}</ref> The Point Tupper plant reached full production in 1974 and AECL purchased the plant in 1975.<ref>{{cite book |last1=Davies |first1=Stanley |title=Is Making Heavy Water Painful? |date=2023 |publisher=Stanley M. Davies |isbn=9798377591016 |pages=218, 232 |edition=1 |url=https://www.amazon.com/dp/B0BXHQFT9T |access-date=30 January 2024}}</ref> Design changes from the Point Tupper plant were carried through as AECL built the Bruce Heavy Water Plant ({{Coord|44.1854|-81.3618|type:landmark_region:CA|name=Bruce Heavy Water Plant|display=inline}}),<ref>Google Earth</ref> which it later sold to [[Ontario Hydro]], to ensure a reliable supply of heavy water for future power plants. The two Nova Scotia plants were shut down in 1985 when their production proved unnecessary.

The [[Bruce Nuclear Generating Station|Bruce Heavy Water Plant]] (BHWP) in [[Ontario]] was the world's largest heavy water production plant with a capacity of 1600 tonnes per year at its peak (800 tonnes per year per full plant, two fully operational plants at its peak). It used the [[Girdler sulfide process]] to produce heavy water, and required 340,000 tonnes of feed water to produce one tonne of heavy water. It was part of a complex that included eight [[CANDU reactor]]s, which provided heat and power for the heavy water plant. The site was located at [[Douglas Point]]/[[Bruce Nuclear Generating Station]] near Tiverton, Ontario, on [[Lake Huron]] where it had access to the waters of the [[Great Lakes (North America)|Great Lakes]].<ref name="CSR on BHWP decommissioning">{{cite web|url=https://www.ceaa-acee.gc.ca/EADDB84F-docs/report_e.pdf| title=Bruce Heavy Water Plant Decommissioning Project |publisher=Canadian Nuclear Safety Commission|access-date=21 February 2018|date=March 2003}}</ref>

AECL issued the construction contract in 1969 for the first BHWP unit (BHWP A). Commissioning of BHWP A was done by Ontario Hydro from 1971 through 1973, with the plant entering service on 28 June 1973, and design production capacity being achieved in April 1974. Due to the success of BHWP A and the large amount of heavy water that would be required for the large numbers of upcoming planned CANDU nuclear power plant construction projects, Ontario Hydro commissioned three additional heavy water production plants for the [[Bruce Nuclear Generating Station|Bruce site]] (BHWP B, C, and D). BHWP B was placed into service in 1979. These first two plants were significantly more efficient than planned, and the number of CANDU construction projects ended up being significantly lower than originally planned, which led to the cancellation of construction on BHWP C & D. In 1984, BHWP A was shut down. By 1993 Ontario Hydro had produced enough heavy water to meet all of its anticipated domestic needs (which were lower than expected due to improved efficiency in the use and recycling of heavy water), so they shut down and demolished half of the capacity of BHWP B. The remaining capacity continued to operate in order to fulfil demand for heavy water exports until it was permanently shut down in 1997, after which the plant was gradually dismantled and the site cleared.<ref name="BHWP performance">{{cite book|last1=DAVIDSON|first1=G. D.|title=Separation of Hydrogen Isotopes|volume=68|date=1978|publisher=American Chemical Society|isbn=978-0841204201|pages=27–39|chapter=Bruce Heavy Water Plant Performance|doi=10.1021/bk-1978-0068.ch002|series=ACS Symposium Series}}</ref><ref name="CHWP 1970–1980">{{cite web|last1=Galley|first1=M.R.|last2=Bancroft|first2=A.R.|title=Canadian Heavy Water Production - 1970 TO 1980|url=https://www.iaea.org/inis/collection/NCLCollectionStore/_Public/13/680/13680421.pdf|access-date=21 February 2018|date=October 1981}}</ref>

AECL is currently researching other more efficient and environmentally benign processes for creating heavy water. This is relevant for CANDU reactors since heavy water represented about 15–20% of the total capital cost of each CANDU plant in the 1970s and 1980s.<ref name="CHWP 1970–1980" />

===Iran===
Since 1996 [[IR-40|a plant]] for production of heavy water was being constructed at Khondab near [[Arak, Iran|Arak]].{{citation needed|date=February 2023}} On 26 August 2006, Iranian President [[Ahmadinejad]] inaugurated the expansion of the country's heavy-water plant. Iran has indicated that the heavy-water production facility will operate in tandem with a 40 MW research reactor that had a scheduled completion date in 2009.<ref>{{cite news |url=https://www.telegraph.co.uk/news/main.jhtml?xml=/news/2006/08/26/uiran.xml |title=Iran's president launches a new nuclear project |publisher=Telegraph.co.uk |date=27 August 2006 |access-date=10 September 2007 |archive-url=https://web.archive.org/web/20070713013652/http://www.telegraph.co.uk/news/main.jhtml?xml=%2Fnews%2F2006%2F08%2F26%2Fuiran.xml |archive-date=13 July 2007 |url-status=dead }}</ref> Iran produced [[deuterated solvents]] in early 2011 for the first time.<ref>{{cite web|url=http://isna.ir/fa/news/92071711508/%D8%A2%D8%A8-%D8%B3%D9%86%DA%AF%DB%8C%D9%86-%D8%A7%D8%B1%D8%A7%DA%A9-%D8%A8%D9%87%D8%A7%D9%86%D9%87-%D8%AC%D9%88%DB%8C%DB%8C-%D8%AC%D8%AF%DB%8C%D8%AF-%D8%BA%D8%B1%D8%A8 |title=آب سنگین اراک، بهانه‌جویی جدید غرب – ایسنا |website=Isna.ir |date= 9 October 2013|access-date=11 January 2017}}</ref> The core of the IR-40 is supposed to be re-designed based on the [[Joint Comprehensive Plan of Action|nuclear agreement]] in July 2015.

Under the [[Joint Comprehensive Plan of Action]], Iran is permitted to store only {{convert|130|t|ST|lk=on}} of heavy water.<ref>{{cite web |title=Iran says it has transferred 11 tons of heavy water to Oman |url=https://www.apnews.com/daa46987ba2d4da98edfcab735aed304 |website=[[AP News]] |access-date=21 October 2018 |language=En |date=22 November 2016}}</ref> Iran exports excess production, making Iran the world's third largest exporter of heavy water.<ref>{{cite news |title=World Digest: March 8, 2016 |url=https://www.washingtonpost.com/national/world-digest-march-8-2016/2016/03/08/e4fcbee4-e53f-11e5-a6f3-21ccdbc5f74e_story.html |newspaper=[[The Washington Post]] |access-date=21 October 2018 |language=En |date=8 March 2016}}</ref><ref>{{cite web |title=OEC – Heavy water (deuterium oxide) (HS92_ 284510) Product Trade, Exporters and Importers |url=https://atlas.media.mit.edu/en/profile/hs92/284510/ |website=[[The Observatory of Economic Complexity]] |access-date=21 October 2018 |archive-url=https://web.archive.org/web/20181021095310/https://atlas.media.mit.edu/en/profile/hs92/284510/ |archive-date=21 October 2018 |url-status=live |language=En}}</ref> In 2023, Iran sells heavy water; customers have proposed a price over 1,000 dollars per liter.<ref>{{Cite web|url=https://www.farsnews.ir/en/news/14020322000167/AEOI-Spkesman-Freign-Csmers-f-Iran%27s-Heavy-Waer-Sanding-in-Line|title=AEOI Spokesman: Foreign Customers of Iran's Heavy Water Standing in Line &#124; Farsnews Agency|website=www.farsnews.ir}}</ref>

===Pakistan===

In Pakistan, there are two heavy water production sites that are based in [[Punjab, Pakistan|Punjab]]. Commissioned in 1995–96, the [[Khushab Nuclear Complex]] is a central element of Pakistan's stockpile program for production of weapon-grade plutonium, deuterium, and tritium for advanced compact warheads (i.e. [[thermonuclear weapons]]). Another [[Multan Heavy Water Production Facility|heavy water facility]] for producing the heavy water is located in Multan, that it sells to nuclear power plants in [[Karachi Nuclear Power Complex|Karachi]] and [[Chashma Nuclear Power Complex|Chashma]].

In early 1980s, Pakistan succeeded in acquiring a tritium purification and storage plant and deuterium and tritium precursor materials from two former East German firms.<ref>{{cite web|url=https://fas.org/nuke/guide/pakistan/facility/khushab.htm |title=Khushab Heavy Water Plant |publisher=Fas.org |access-date=14 August 2010}}</ref> Unlike India and Iran, the heavy water produced by Pakistan is not exported nor available for purchase to any nation and is solely used for its weapons complex and energy generation at its local nuclear power plants.

===Other countries===
Romania produced heavy water at the now-decommissioned [[Drobeta-Turnu Severin|Drobeta]] Girdler sulfide plant for domestic and export purposes.<ref>{{cite web|url=http://peopletales.blogspot.com/2015/04/heavy-water-candu-reactors-and-living.html |title=History or Utopia: 45) Heavy water, nuclear reactors and... the living water |website=Peopletales.blogspot.com |access-date=11 January 2017}}</ref> France operated a small plant during the 1950s and 1960s.{{citation needed|date=January 2016}}

==Applications==
===Nuclear magnetic resonance===
Deuterium oxide is used in [[nuclear magnetic resonance spectroscopy]] when using water as a solvent if the [[nuclide]] of interest is hydrogen. This is because the signal from light-water ({{sup|1}}H{{sub|2}}O) solvent molecules would overwhelm the signal from the molecule of interest dissolved in it. Deuterium has a different [[magnetic moment]] and therefore does not contribute to the [[H-1 NMR|{{sup|1}}H-NMR]] signal at the hydrogen-1 resonance frequency.

For some experiments, it may be desirable to identify the labile hydrogens on a compound, that is hydrogens that can easily exchange away as H{{sup|+}} ions on some positions in a molecule. With addition of D{{sub|2}}O, sometimes referred to as a ''D{{sub|2}}O shake'',<ref>{{cite web |url= https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(Morsch_et_al.)/17%3A_Alcohols_and_Phenols/17.11%3A_Spectroscopy_of_Alcohols_and_Phenols |title= 17.11: Spectroscopy of Alcohols and Phenols |date= 26 August 2015 }}</ref> labile hydrogens exchange between the compound of interest and the solvent, leading to replacement of those specific {{sup|1}}H atoms in the compound with {{sup|2}}H. These positions in the molecule then do not appear in the {{sup|1}}H-NMR spectrum.

===Organic chemistry===
Deuterium oxide is often used as the source of deuterium for preparing specifically labelled [[isotopologue]]s of organic compounds. For example, C-H bonds adjacent to ketonic carbonyl groups can be replaced by C-D bonds, using acid or base catalysis. [[Trimethylsulfoxonium iodide]], made from [[dimethyl sulfoxide]] and [[methyl iodide]] can be recrystallized from deuterium oxide, and then dissociated to regenerate methyl iodide and dimethyl sulfoxide, both deuterium labelled. In cases where specific double labelling by deuterium and tritium is contemplated, the researcher must be aware that deuterium oxide, depending upon age and origin, can contain some tritium.

===Infrared spectroscopy===
Deuterium oxide is often used instead of water when collecting [[Fourier transform spectroscopy|FTIR]] spectra of proteins in solution. H{{sub|2}}O creates a strong band that overlaps with the [[amide]] I region of proteins. The band from D{{sub|2}}O is shifted away from the amide I region.

===Neutron moderator===
Heavy water is used in certain types of [[nuclear reactors]], where it acts as a [[neutron moderator]] to slow down neutrons so that they are more likely to react with the [[fissile]] [[uranium-235]] than with [[uranium-238]], which captures neutrons without fissioning.
The CANDU reactor uses this design. Light water also acts as a moderator, but because light water absorbs more [[neutron]]s than heavy water, reactors using light water for a reactor moderator must use [[enriched uranium]] rather than natural uranium, otherwise [[Critical mass|criticality]] is impossible. A significant fraction of outdated power reactors, such as the [[RBMK]] reactors in the USSR, were constructed using normal water for cooling but [[graphite-moderated reactor|graphite as a moderator]]. However, the danger of graphite in power reactors (graphite fires in part led to the [[Chernobyl disaster]]) has led to the discontinuation of graphite in standard reactor designs.

The breeding and extraction of plutonium can be a relatively rapid and cheap route to building a [[nuclear weapon]], as chemical separation of plutonium from fuel is easier than [[isotopic separation]] of U-235 from natural uranium.
Among current and past [[nuclear weapons states]], Israel, India, and North Korea<ref>{{Cite web|url=http://www-pub.iaea.org/MTCD/publications/PDF/TRS407_scr/D407_scr1.pdf|title=Heavy Water Reactors: Status and Projected Development}}</ref> first used plutonium from heavy water moderated reactors burning [[natural uranium]], while China, South Africa and Pakistan first built weapons using [[highly enriched uranium]].

The [[Uranverein|Nazi nuclear program]], operating with more modest means than the contemporary Manhattan Project and hampered by many leading scientists having been driven into exile (many of them ending up working for the Manhattan Project), as well as continuous infighting, wrongly dismissed graphite as a moderator due to not recognizing the effect of impurities. Given that [[isotope separation]] of uranium was deemed too big a hurdle, this left heavy water as a potential moderator. Other problems were the ideological aversion regarding what propaganda dismissed as "[[Jewish physics]]" and the mistrust between those who had been enthusiastic Nazis even before 1933 and those who were ''[[Mitläufer]]'' or trying to keep a low profile. In part due to allied sabotage and commando raids on [[Norsk Hydro]] (then the world's largest producer of heavy water) as well as the aforementioned infighting, the German nuclear program never managed to assemble enough uranium and heavy water in one place to achieve [[Critical mass|criticality]] despite possessing enough of both by the end of the war.

In the U.S., however, the first experimental atomic reactor (1942), as well as the [[Manhattan Project]] Hanford production reactors that produced the plutonium for the [[Trinity test]] and [[Fat Man]] bombs, all used pure carbon (graphite) neutron moderators combined with normal water cooling pipes. They functioned with neither enriched uranium nor heavy water. Russian and British plutonium production also used graphite-moderated reactors.

There is no evidence that civilian heavy water power reactors—such as the CANDU or [[Atucha I nuclear power plant|Atucha]] designs—have been used to produce military fissile materials. In nations that do not already possess nuclear weapons, nuclear material at these facilities is under [[IAEA]] safeguards to discourage any diversion.

Due to its potential for use in [[nuclear weapon]]s programs, the possession or import/export of large industrial quantities of heavy water are subject to government control in several countries. Suppliers of heavy water and heavy water production technology typically apply [[IAEA]] (International Atomic Energy Agency) administered safeguards and material accounting to heavy water. (In Australia, the ''Nuclear Non-Proliferation (Safeguards) Act 1987''.) In the U.S. and Canada, non-industrial quantities of heavy water (i.e., in the gram to kg range) are routinely available without special license through chemical supply dealers and commercial companies such as the world's former major producer [[Ontario Hydro]].

===Neutrino detector===
The [[Sudbury Neutrino Observatory]] (SNO) in [[Greater Sudbury|Sudbury]], [[Ontario]] uses 1,000 tonnes of heavy water on loan from [[Atomic Energy of Canada Limited]]. The [[neutrino detector]] is {{convert|6800|ft|m}} underground in a mine, to shield it from [[muon]]s produced by [[cosmic ray]]s. SNO was built to answer the question of whether or not electron-type [[neutrino]]s produced by fusion in the [[Sun]] (the only type the Sun should be producing directly, according to theory) might be able to turn into other types of neutrinos on the way to Earth. SNO detects the [[Cherenkov radiation]] in the water from high-energy electrons produced from [[electron neutrino|electron-type neutrino]]s as they undergo charged current (CC) interactions with [[neutron]]s in [[deuterium]], turning them into protons and electrons (however, only the electrons are fast enough to produce Cherenkov radiation for detection).

SNO also detects neutrino electron scattering (ES) events, where the neutrino transfers energy to the electron, which then proceeds to generate Cherenkov radiation distinguishable from that produced by CC events. The first of these two reactions is produced only by electron-type neutrinos, while the second can be caused by all of the neutrino flavors. The use of deuterium is critical to the SNO function, because all three "flavours" (types) of neutrinos<ref>{{cite web |url=http://www.sno.phy.queensu.ca/sno/sno2.html |title=The SNO Detector |publisher=The Sudbury Neutrino Observatory Institute, Queen's University at Kingston |access-date=10 September 2007 |archive-date=7 May 2021 |archive-url=https://web.archive.org/web/20210507204823/https://sno.phy.queensu.ca/sno/sno2.html |url-status=dead }}</ref> may be detected in a third type of reaction as well, neutrino-disintegration, in which a neutrino of any type (electron, [[muon neutrino|muon]], or [[tau neutrino|tau]]) scatters from a deuterium nucleus ([[deuteron]]), transferring enough energy to break up the loosely bound deuteron into a free [[neutron]] and [[proton]] via a neutral current (NC) interaction.

This event is detected when the free neutron is absorbed by [[Chlorine-35|<sup>35</sup>Cl]]<sup>−</sup> present from [[NaCl]] deliberately dissolved in the heavy water, causing emission of characteristic capture gamma rays. Thus, in this experiment, heavy water not only provides the transparent medium necessary to produce and visualize Cherenkov radiation, but it also provides deuterium to detect exotic mu type (μ) and tau (τ) neutrinos, as well as a non-absorbent moderator medium to preserve free neutrons from this reaction, until they can be absorbed by an easily detected neutron-activated isotope.

===Metabolic rate and water turnover testing in physiology and biology===
{{main|Doubly labeled water test}}
Heavy water is employed as part of a mixture with H{{sub|2}}{{sup|18}}O for a common and safe test of mean metabolic rate in humans and animals undergoing their normal activities.The elimination rate of deuterium alone is a measure of body water turnover. This is highly variable between individuals and depends on environmental conditions as well as subject size, sex, age and physical activity.<ref>{{Cite journal|last1=Yamada|first1=Yosuke|last2=Zhang|first2=Xueying|last3=Henderson|first3=Mary E. T.|last4=Sagayama|first4=Hiroyuki|last5=Pontzer|first5=Herman|last6=Speakman|first6=John R. |date=2022|title= Variation in human water turnover associated with environmental and lifestyle factors|journal=Science|language=en|volume=378|issue=6622|pages=909–915|doi=10.1126/science.abm8668|pmid=36423296|pmc=9764345 |bibcode=2022Sci...378..909I }}</ref>

===Tritium production===
{{See also|Tritium#Deuterium}}
[[Tritium]] is the active substance in [[tritium illumination|self-powered lighting]] and controlled nuclear fusion, its other uses including [[autoradiography]] and [[radioactive label]]ing. It is also used in [[nuclear weapon design]] for [[boosted fission weapon]]s and [[tritium#Neutron initiator|initiators]]. Tritium undergoes [[beta decay]] into [[helium-3]], which is a stable, but rare, isotope of helium that is itself highly sought after. Some tritium is created in [[heavy water moderated reactor]]s when deuterium captures a neutron. This reaction has a small [[Neutron cross-section|cross-section]] (probability of a single neutron-capture event) and produces only small amounts of tritium, although enough to justify cleaning tritium from the moderator every few years to reduce the environmental risk of tritium escape. Given that helium-3 is a [[neutron poison]] with orders of magnitude higher capture cross section than any component of heavy or tritiated water, its accumulation in a heavy water neutron moderator or [[target (Physics)|target]] for tritium production must be kept to a minimum.

Producing a lot of tritium in this way would require reactors with very high neutron fluxes, or with a very high proportion of heavy water to [[nuclear fuel]] and very low [[neutron absorption]] by other reactor material. The tritium would then have to be recovered by [[isotope separation]] from a much larger quantity of deuterium, unlike production from [[lithium-6]] (the present method), where only chemical separation is needed.

Deuterium's absorption cross section for [[thermal neutron]]s is 0.52 milli[[barn (unit)|barn]] (5.2 × 10{{sup|−32}} m{{sup|2}}; 1 barn = 10{{sup|−28}} m{{sup|2}}), while those of [[oxygen-16]] and [[oxygen-17]] are 0.19 and 0.24 millibarn, respectively. {{sup|17}}O makes up 0.038% of natural [[oxygen]], making the overall cross section 0.28 millibarns. Therefore, in D{{sub|2}}O with natural oxygen, 21% of [[neutron capture]]s are on oxygen, rising higher as {{sup|17}}O builds up from neutron capture on {{sup|16}}O. Also, {{sup|17}}O may emit an [[alpha particle]] on neutron capture, producing radioactive [[carbon-14]].

==See also==
{{Portal|Water}}
* [[Cold fusion]]
* [[Deuterium-depleted water]]
* [[Interstellar ice]]

==References==
{{Reflist}}

==External links==
* [http://www.periodicvideos.com/videos/mv_heavywater.htm Heavy Water] and [http://www.periodicvideos.com/videos/mv_heavywater_part2.htm Heavy Water – Part II] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* [https://web.archive.org/web/20160227012413/http://fas.org/nuke/intro/nuke/heavy.htm Heavy Water Production], Federation of American Scientists
* [https://web.archive.org/web/20040721172828/http://www.cns-snc.ca/Bulletin/A_Miller_Heavy_Water.pdf Heavy Water: A Manufacturer's Guide for the Hydrogen Century]
* [http://www.straightdope.com/mailbag/mheavywater.html Is "heavy water" dangerous?] {{Webarchive|url=https://web.archive.org/web/20050204232753/http://www.straightdope.com/mailbag/mheavywater.html |date=4 February 2005 }} Straight Dope Staff Report. 9 December 2003
* [https://web.archive.org/web/20051210084630/http://alsos.wlu.edu/qsearch.aspx?browse=science%2FHeavy+Water Annotated bibliography for heavy water from the Alsos Digital Library for Nuclear Issues]
* [https://web.archive.org/web/20071216010940/http://www.popsci.com/popsci/how20/a07160a72252c010vgnvcm1000004eecbccdrcrd.html Ice is supposed to float, but with a little heavy water, you can make cubes that sink]
* [http://www.o8ode.ru/article/eng/Isotopic_effects_of_heavy_water_in_biological_objects Isotopic Effects of Heavy Water in Biological Objects] Oleg Mosin, Ignat Ignatov
* [http://scitation.aip.org/content/aip/journal/jcp/41/3/10.1063/1.1725946 J. Chem. Phys. 41, 1964]
* [https://www.hwb.gov.in/mou-between-hwb-and-ms-clearsynth-mumbai-sale-20-tonnes-heavy-water-year-its-non-nuclear-0 MOU between HWB and M/s Clearsynth] MOU between HWB and M/s Clearsynth, Mumbai for sale of 20 tonnes of Heavy Water in a year for its non-nuclear applications.

{{Water}}
{{Molecules detected in outer space}}
{{Oxygen compounds}}
{{Hydrides by group}}
{{List of NMR solvents}}
{{Authority control}}

{{DEFAULTSORT:Heavy water}}
[[Category:Deuterated compounds]]
[[Category:Deuterated solvents]]
[[Category:Forms of water]]
[[Category:Neutron moderators]]
[[Category:Nuclear reactor coolants]]
[[Category:Oxygen compounds]]