View source for Heavy water

{{Chembox new
|   Name = Heavy water (at 100% D enrichment): D<sub>2</sub>O
|   ImageFile = Water molecule 3D.svg 
|   ImageSize = 120px 
|   ImageName = All types of isotopically substituted water molecules have this structure. 
|   IUPACName = Deuterium oxide 
|   OtherNames = Water d<sub>2</sub><br/>Heavy water<br/>Dideuterium monoxide<br/>
| Section1 = {{Chembox Identifiers
|   CASNo = 7789-20-0 
|   RTECS = ZC0230000 
  }}
| Section2 = {{Chembox Properties
|   Formula = D<sub>2</sub>O 
|   MolarMass = 20.04 g/mol 
|   Appearance = transparent, colorless liquid 
|   Density = 1.1056 g/mL, liquid (20°C)<br /> 1.0177 g/cm<sup>3</sup>, solid (at m.p) 
|   BoilingPt = 101.4&nbsp;°C, 214.56&nbsp;°F (374.55&nbsp;°K) 
|   MeltingPt = 3.82&nbsp;°C, 38.88&nbsp;°F (276.97&nbsp;°K) 
|   Viscosity = 0.00125 [[pascal second|Pa·s]] at 20 °C 
|   Dipole = 1.87 [[Debye|D]] 
  }}
| Section7 = {{Chembox Hazards
|   ExternalMSDS = [http://ptcl.chem.ox.ac.uk/MSDS/DE/deuterium_oxide.html External MSDS] 
|   MainHazards =  
|   NFPA-H = 0 
|   NFPA-F = 0 
|   NFPA-R = 0 
  }}
| Section8 = {{Chembox Related
|   Function = [[solvent]]s 
|   OtherFunctn = [[acetone]]; [[methanol]] 
|   OtherCpds = [[water vapor]]; [[ice]]}}
}}
'''Heavy water''' is [[water (molecule)|water]] which contains a higher proportion than normal of the [[isotope]] [[deuterium]], as '''deuterium oxide''', D<sub>2</sub>O or ²H<sub>2</sub>O, or as '''deuterium protium oxide''', HDO or ¹H²HO.<ref>{{GoldBookRef|title=heavy water|file=H02758}}</ref> Its physical and chemical properties are somewhat similar to those of [[Water (molecule)|water]], H<sub>2</sub>O. Heavy water may contain as much as 100% D<sub>2</sub>O, and usually the term refers to water which is highly enriched in deuterium. The isotopic substitution with deuterium alters the [[bond energy]] of the hydrogen-oxygen bond in water, altering the physical, chemical, and especially biological properties of the pure or highly-enriched substance to a larger degree than is found in most isotope-substituted chemical compounds. 

Heavy water should not be confused with [[hard water]] or with [[tritiated water]].

== Other meanings ==
===Semiheavy water===
'''Semiheavy water''', HDO, exists whenever there is water with hydrogen-1 (or [[Hydrogen atom|protium]]) and deuterium present in the mixture. This is because hydrogen atoms (hydrogen-1 and deuterium) are rapidly exchanged between water molecules. Water containing 50% H and 50% D in its hydrogen actually contains about 50% HDO and 25% each of H<sub>2</sub>O and D<sub>2</sub>O, in [[dynamic equilibrium]].
Semiheavy water, HDO, occurs naturally in regular water at a proportion of about 1 molecule in 3,200 (each hydrogen has a probability of 1 in 6,400 of being D). Heavy water, D<sub>2</sub>O, by comparison, occurs naturally at a proportion of about 1 molecule in 41 million (i.e., 1 in 6,400<sup>2</sup>). This makes semiheavy water actually far more prevalent than 'normal' heavy water.

=== Heavy-oxygen water ===
A common type of heavy-[[oxygen]] water H<sub>2</sub><sup>18</sup>O is available commercially for use as a non-radioactive isotopic tracer (see [[doubly-labeled water]] for discussion), and qualifies as "heavy water" insofar as having a higher density than normal water (in this case, similar density to deuterium oxide). At higher expense (due to the greater difficulty in separation of O-17, a less common heavy isotope of oxygen), water is available in which the oxygen is enriched to varying degrees with <sup>17</sup>O. However, these types of heavy-isotope water are rarely referred to as "heavy water", as they do not contain the deuterium which gives D<sub>2</sub>O its characteristically different nuclear and biological properties. Heavy-oxygen waters with normal hydrogen, for example, would not be expected to show any toxicity whatsoever (see discussion of toxicity below).

==Physical properties (with comparison to light water)==
{| class="wikitable"
|-
! align="left" | Property || D<sub>2</sub>O (Heavy water) || H<sub>2</sub>O (Light water)
|-
| Freezing point (°C) ||align="center"| 3.82 ||align="center"| 0.0
|-
| Boiling point (°C) ||align="center"| 101.4 ||align="center"| 100.0
|-
| Density (at 20°C, g/[[millilitre|mL]]) ||align="center"| 1.1056 ||align="center"| 0.9982
|-
| Temp. of maximum density (°C) ||align="center"| 11.6 ||align="center"| 4.0
|-
| Viscosity (at 20°C, [[millipascal|mPa]]·[[second|s]]) ||align="center"| 1.25 ||align="center"| 1.005
|-
| Surface tension (at 25°C, [[microjoule|μJ]])<!--- 1 dyn-cm = 0.1 μJ = 100 nJ ---> ||align="center"| 7.193 ||align="center"| 7.197
|-
| Heat of fusion ([[calorie|cal]]/[[mole (unit)|mol]]) ||align="center"| 1,515 ||align="center"| 1,436
|-
| Heat of vaporisation (cal/mol) ||align="center"| 10,864 ||align="center"| 10,515
|-
| pH (at 25°C)  ||align="center"| 7.41 (sometimes "pD") ||align="center"| 7.00
|-
|}

No physical properties are listed for "pure" semi-heavy water, because it cannot be isolated in bulk quantities. In the liquid state, a few water molecules are always in an [[Self-ionisation of water|ionised state]], which means the hydrogen atoms can exchange among different oxygen atoms. A sample of hypothetical "pure" semi-heavy water would rapidly transform into a dynamic mixture of 25% light water, 25% heavy water, and 50% semi-heavy water.

''Physical properties obvious by inspection:'' Heavy water is 10.6% more dense than ordinary water, a difference which is nearly impossible to notice in a sample of it (which otherwise looks and tastes exactly like normal water). One of the few ways to demonstrate heavy water's physically different properties without equipment, is to freeze a sample and drop it into normal water. Ice made from heavy water ''sinks'' in normal water. If the normal water is ice-cold this phenomenon may be observed long enough for a good demonstration, since heavy-water ice has a slightly higher melting-temperature (3.8&nbsp;°C) than normal ice, and thus holds up very well in ice-cold normal water. <ref>{{cite web |url=http://www.popsci.com/popsci/how20/a07160a72252c010vgnvcm1000004eecbccdrcrd.html |title=How 2.0 |accessdate=2008-01-21 |last=Gray |first=Theodore |coauthors= |date=2007 |work= |publisher=Popular Science}}</ref>

==History== 
[[Harold Urey]] discovered the isotope [[deuterium]] in [[1931]] and was later able to concentrate it in water.<ref>{{cite journal
 | author = H. C. Urey, Ferdinand G. Brickwedde, G. M. Murphy
 | title = A Hydrogen Isotope of Mass 2
 | journal = Physical Review
 | year = 1932
 | volume = 39
 | pages = 164–165
 | doi = 10.1103/PhysRev.39.164
 }}</ref> Urey's mentor [[Gilbert Newton Lewis]] isolated the first sample of pure heavy water by [[electrolysis]] in [[1933]].<!--
{{cite journal
 | author = Lewis
 | title =  The Isotopes of Hydrogen
 | journal = Journal of the American Chemical Society 
 | year = 1933 
 | volume = 55 
 | pages = 1297  
 | doi = 10.1021/ja01330a511
  }}
{{cite journal
 | author = Washburn and Urey
 | title = Concentration of the H2 Isotope of Hydrogen by the Fractional Electrolysis of Water
 | journal = Proc. Nut. Acad. Sci.,  
 | year = 1932
 | volume = 18 
 | pages = 496 
 | url =  http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1076263&blobtype=pdf
 }}--> [[George de Hevesy]] and Hoffer 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. The history of large-quantity production and use of heavy water in early nuclear experiments is given below.<ref>{{cite paper
  | title =An Early History of Heavy Water
  | author =Chris Waltham
  | publisher =Department of Physics and Astronomy, University of British Columbia
  | date = [[20 June]] [[2002]]
  | url =http://arxiv.org/pdf/physics/0206076.pdf
  | format =PDF
}}</ref>

==Effect on biological systems==
Heavy isotopes of chemical elements have very slightly different chemical behaviors, but for most elements the differences in chemical behavior between isotopes are far too small to use, or even detect. For hydrogen, however, this is not true. The larger chemical isotope-effects seen with deuterium and [[tritium]] manifest because bond energies in chemistry are determined in quantum mechanics by equations in which the quantity of [[reduced mass]] of the nucleus and electrons appears. This quantity is altered in heavy-hydrogen compounds (of which deuterium oxide is the most common and familiar) far more than for heavy-isotope substitution in other chemical elements. This isotope effect of heavy hydrogen is magnified further in biological systems, which are very sensitive to small changes in the solvent properties of water.

Heavy water is the only known chemical substance which affects the period of [[circadian rhythm|circadian oscillations]], consistently increasing them. The effect is seen 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'' |authors= Pittendrigh, C. S.; Caldarola, P. C.; Cosbey, E. S. |journal= [[Proc. Natl. Acad. Sci. USA]] |volume= 70 |issue= 7 |month= July |year= 1973 |pages= 2037–2041 |pmid= 4516204 }}</ref>

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 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]] formation 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.

== Effect on animals ==
Experiments in mice, rats, and dogs<ref name="k">{{cite journal |pmid=10535697 |title=Pharmacological uses and perspectives of heavy water and deuterated compounds |author=D. J. Kushner, Alison Baker, and T. G. Dunstall |journal=Can. J. Physiol. Pharmacol. |volume=77 |issue=2 |pages=79–88 |year=1999 |quote=used in boron neutron capture therapy ... D2O is more toxic to malignant than normal animal cells ... Protozoa are able to withstand up to 70% D20. Algae and bacteria can adapt to grow in 100% D2O | doi = 10.1139/cjpp-77-2-79 <!--Retrieved from CrossRef by DOI bot-->}}</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 kills [[fish]], [[tadpole]]s, [[flatworm]]s, and [[drosophila]]. Mammals such as [[rat]]s given heavy water to drink die after a week, at a time when their body water approaches about 50% deuteration. 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 due to deuterium's action in generally inhibiting cell division. Deuterium oxide is used to enhance [[boron neutron capture therapy]].<ref name="k"/> It is more toxic to malignant cells than normal cells but the concentrations needed are too high for regular use.<ref name="k"/> As in chemotherapy, deuterium-poisoned mammals die of a failure of bone marrow (bleeding and infection) and intestinal-barrier functions ([[diarrhea]] and fluid loss).

Notwithstanding 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"/> Full replacement with heavy atom isotopes can be accomplished in higher organisms with other non-radioactive heavy isotopes (such as carbon-13, nitrogen-15, and oxygen-18), but this cannot be done for the stable heavy isotope of hydrogen.

== Toxicity in humans ==
Because it would take a very great deal of heavy water to replace 25% to 50% of a human being's body water (which in turn is 70% of body weight) with heavy water, accidental or intentional [[poison]]ing with heavy water is unlikely to the point of practical disregard. For a poisoning, large amounts of heavy water would need to be ingested without significant normal water intake for many days to produce any noticeable toxic effects (although in a few tests, volunteers drinking large amounts of heavy water have reported dizziness, a possible effect of density changes in the fluid in the inner ear). For example, a 70 kg human containing 50 kg of water and drinking 3 liters of pure heavy water per day, would need to do this for almost 5 days to reach 25% deuteration, and for about 11 days to approach 50% deuteration. Thus, it would take a week of drinking nothing but pure heavy water for a human to begin to feel ill, and 10 days to 2 weeks (depending on water intake) for severe poisoning and death. In the highly unlikely event that a human were to receive a toxic dose of heavy water, the treatment would involve the use of intravenous water replacement (due to possible [[intestinal dysfunction]] and problems with absorption of fluids). This would be done via 0.9% (normal physiologic) saline solution with other salts as needed, perhaps in conjunction with [[diuretics]].

Oral doses of heavy water in the multi-gram range, along with heavy oxygen <sup>18</sup>O, are routinely used in human metabolic experiments. See [[doubly-labeled water]] testing. Since 1 in every 6400 hydrogen atoms is deuterium, a 50 kg human containing 32 kg of body water would normally contain enough deuterium (about 1.1 gram) to make 5.5 grams 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 --->

== Confused report of a "heavy water" contamination incident ==
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 the employee water cooler. 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 which could induce heavy water toxicity per se, 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) |accessdate=2007-09-10}}</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 was left with the impression that heavy water is normally radioactive and more severely toxic than it 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 employees would be expected to get as much as 25% of their daily drinking water from such a source.<ref>
{{cite web  
|url=http://nl.newsbank.com/nl-search/we/Archives?p_product=DN&s_site=philly&p_multi=PI{{!}}DN&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
|title=Radiation Punch Nuke Plant Worker Charged With Spiking Juice
|publisher=[[Philadelphia Daily News]]
|date=[[March 6]], [[1990]]
|accessdate=2006-11-30
|author=[[Associated Press]]
}}
</ref>

==Production==
On [[Earth]], semiheavy water, HDO, occurs naturally in regular water at a proportion of about 1 molecule in 3200. This means that 1 in 6400 hydrogen atoms is deuterium, which is 1 part in 3200 by weight (hydrogen weight). The HDO may be separated from regular water by [[distillation]] or [[electrolysis]] and also by various chemical exchange processes, all of which exploit a [[kinetic isotope effect]].  (For more information about the isotopic distribution of deuterium in water, see [[Vienna Standard Mean Ocean Water]].)

The difference in mass between the two hydrogen isotopes translates into a difference in the [[zero-point energy]] and thus into a slight difference in the speed at which the reaction proceeds. Once HDO becomes a significant fraction of the water, heavy water will become more prevalent as water molecules trade hydrogen atoms very frequently. To produce pure heavy water by distillation or electrolysis requires a large cascade of stills or electrolysis chambers, and consumes large amounts of power, so the chemical methods are generally preferred. The most important chemical method is the [[Girdler sulfide process]].

==={{USA}}===
In 1953, the United States began using heavy water in [[plutonium]] production reactors at the [[Savannah River Site]].  The first of the five heavy water reactors came online in 1953, and the last was placed in cold shutdown in 1996. The SRS 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 Plant, South Carolina in 1952.  The SRP was operated by [[DuPont]] for the USDOE until [[April 1]], [[1989]] at which time the operation was taken over by [[Westinghouse Electric Company|Westinghouse]].

==={{NOR}}===
In [[1934]], [[Norsk Hydro]] built the first commercial heavy water plant at [[Vemork]], [[Tinn]], with a capacity of 12 tonnes per year. From [[1940]] and throughout [[World War II]], the plant was under [[Nazi Germany|German]] control and the allies decided to destroy the plant and its heavy water to inhibit German development of nuclear weapons. In late [[1942]], a raid by [[United Kingdom|British]] [[paratrooper]]s failed when the gliders they were in crashed. All the raiders were killed in the crash or shot by German army troops. But in the night of [[27 February]] [[1943]] [[Operation Gunnerside]] succeeded. Norwegian commandos managed to demolish small but key bits of the electrolytic cells, dumping the accumulated heavy water down the factory drains. Arguably{{Clarifyme|couldn't find what this refers to|date=March 2008}} (see below) this prevented Germany from building a nuclear reactor (German nuclear weapons would not have automatically followed the reactor for many reasons{{Clarifyme|date=March 2008}}). The Norsk Hydro operation is one of the great commando/sabotage operations of the war.

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 ''M/F&nbsp;Hydro'' carrying the heavy water across [[Lake Tinn]], at the cost of 14 Norwegian civilians, and most of the heavy water was presumably lost. A few of the barrels were only half full, and therefore could float, and may have been salvaged and transported to Germany. (These events were dramatized in the 1965 movie, ''[[The Heroes of Telemark]]''.)

However, 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</sub>O. Despite the apparent size of shipment, the total quantity of pure heavy water was quite small, most barrels only containing between 1/2–1% pure heavy water.  The Germans would have needed a total of about 5 tons of heavy water to get a nuclear reactor running.  <!--reference: documentary on Nova / Hitlers Sunken Treasure--> The manifest clearly indicated that there was only half a ton of heavy water being transported to Germany.  The Hydro was carrying far too little heavy water for even one reactor, let alone the 10 or more tons needed to make enough plutonium for a nuclear weapon. The Hydro shipment on [[20 February]] [[1944]] was probably destined for an experimental reactor project.

==={{CAN}}===
As part of its contribution to the [[Manhattan Project]], Canada built and operated a 6 tonnes per year electrolytic heavy water plant at [[Trail, British Columbia|Trail, BC]], which started operation in 1943. 

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|Glace Bay]] (by Deuterium of Canada Limited) and [[Port Hawkesbury, Nova Scotia|Port Hawkesbury]], [[Nova Scotia]] (by General Electric Canada). These plants proved to have significant design, construction and production problems and so AECL built the Bruce Heavy Water Plant, 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 to be unnecessary.

The Bruce Heavy Water Plant in [[Ontario]] was the world's largest heavy water production plant with a capacity of 700 tonnes per year. 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 8 [[CANDU reactor]]s which provided heat and power for the heavy water plant. The site was located at [[Douglas Point]] in [[Bruce County]] on [[Lake Huron]] where it had access to the waters of the [[Great Lakes (North America)|Great Lakes]].

The Bruce plant was commissioned in [[1979]] to provide heavy water for a large increase in Ontario's nuclear power generation. The plants proved to be significantly more efficient than planned and only three of the planned four units were eventually commissioned. In addition, the nuclear power programme was slowed down and effectively stopped due to a perceived oversupply of electricity, later shown to be temporary, in [[1993]]. Improved efficiency in the use and recycling of heavy water plus the over-production at Bruce left Canada with enough heavy water for its anticipated future needs. Also, the Girdler process involves large amounts of [[hydrogen sulfide]], raising environmental concerns if there should be a release. The Bruce heavy-water plant was shut down in [[1997]], after which the plant was gradually dismantled and the site cleared.

[[Atomic Energy of Canada Limited]] (AECL) is currently researching other more efficient and environmentally benign processes for creating heavy water. This is essential for the future of the CANDU reactors since heavy water represents about 20% of the capital cost of each reactor.

======
[[India]] is the world's second largest producer of heavy water through its [http://www.heavywaterboard.org/ Heavy Water Board].

==={{IRN}}===
On [[August 26]], [[2006]], Iranian President [[Ahmadinejad]] inaugurated an expansion of the country's heavy-water plant near [[Arak, Iran|Arak]].  Iran has indicated that the heavy-water production facility will operate in tandem with a 40 MW research reactor that has a scheduled completion date in [[2009]].<ref>{{cite news |url=http://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]]|accessdate=2007-09-10}}</ref>
In an interview which aired on the Iranian News Channel (IRINN) on [[August 27]], [[2006]], Iranian Nuclear Chief Mohammad Sa'idi claimed that heavy water could be used to treat AIDS and cancer. Daily consumption was recommended.<ref>"[http://memri.org/bin/articles.cgi?Page=archives&Area=sd&ID=SP127506 Iranian Nuclear Chief Mohammad Sa'idi Explains Why Iran Produces Heavy Water: Drinking It Helps Fight Cancer and AIDS]" aired on the Iranian News Channel (IRINN) on [[August 27]], [[2006]].</ref>

===Other countries===
{{ARG}} is another declared producer of heavy water, using an ammonia/hydrogen exchange based plant supplied by Switzerland's Sulzer company.

{{ROM}} also produces heavy water at the Drobeta Girdler Sulfide plant and has exported from time to time.

 operated a small plant during the 1950s and 1960s.

{{UK}} The Department of Atomic Energy built a station at [[Loch Morar]] in 1947, possibly investigating using the loch as a source of heavy water.<ref>[http://www.kcl.ac.uk/lhcma/pro/p-ab16b.htm Liddell Hart Centre for Military Archives Nuclear History Database]</ref>

==Applications==
===Nuclear magnetic resonance===
Deuterium oxide is used in [[nuclear magnetic resonance spectroscopy]] when the solvent of interest is water and the [[nuclide]] of interest is hydrogen. This is because the signal from the water solvent would interfere with the signal from the molecule of interest. Deuterium has a different [[magnetic moment]] from [[hydrogen]] and therefore does not contribute to the NMR signal at the hydrogen resonance frequency.

===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 can react with the [[uranium]] in the reactor.  
The [[CANDU reactor]] uses this design. Light water also acts as a moderator but because light water absorbs more [[neutrons]] than heavy water, reactors using light water must use [[enriched uranium]] rather than natural uranium, otherwise [[Critical mass|criticality]] is impossible.  The use of heavy water essentially increases the efficiency of the nuclear reaction.

Because of this, [[heavy water reactor]]s will be more efficient at breeding [[plutonium]] (from [[uranium-238]]) or [[uranium-233]] (from [[thorium-232]]) than a comparable light-water reactor, leading them to be of greater concern in regards to [[nuclear proliferation]].  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.  Heavy water moderated research reactors or specifically-built plutonium breeder reactors have been used for this purpose by most, if not all, states which possess [[nuclear weapon]]s, although historically the first nuclear weapons were produced without it. (Pure carbon may be used as a moderator, even in unenriched uranium nuclear reactors. Thus, in the U.S., the first experimental atomic reactor (1942), as well as the [[Manhattan Project]] Hanford production reactors which produced the plutonium for the [[Trinity test]] and [[Fat Man]] bombs, all used pure carbon neutron moderators and functioned with neither enriched uranium nor heavy water).

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 for military production of fissile materials.  In states which do not already possess nuclear weapons, the nuclear material at these facilities is under [[IAEA]] safeguards to discourage any such diversion.

Due to its potential for use in [[nuclear weapons]] 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 through chemical supply dealers, and directly commercial companies such as the world's former major producer [[Ontario Hydro]], without special license. Current (2006) cost of a kilogram of 99.98% reactor-purity heavy water, is about $600 to $700. Smaller quantities of reasonable purity (99.9%) may be purchased from chemical supply houses at prices of roughly $1 per gram.

===Neutrino detector===
The [[Sudbury Neutrino Observatory]] (SNO) in [[Greater Sudbury|Sudbury]], [[Ontario]] uses 1000 tonnes of heavy water on loan from [[Atomic Energy of Canada Limited]]. The [[neutrino detector]] is 6800 feet underground in a deep mine, in order to shield it from [[muons]] produced by [[cosmic rays]]. 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 [[Čerenkov radiation]] in the water from high-energy electrons produced from electron-type [[neutrino]]s as they undergo reactions with [[neutron]]s in [[deuterium]], turning them into protons and electrons (only the electrons move fast enough to be detected in this manner). SNO also detects the same radiation from neutrino↔electron scattering events, which again produces high energy electrons. These two reactions are produced only by electron-type neutrinos. 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 |accessdate=2007-09-10}}</ref> may be detected in a third type of reaction, neutrino-disintegration, in which a neutrino of any type (electron, muon, or tau) scatters from a deuterium nucleus ([[deuteron]]), transferring enough energy to break up the loosely-bound deuteron into a free [[neutron]] and [[proton]]. This event is detected when the free neutron is absorbed by <sup>35</sup>Cl<sup>−</sup> present from NaCl which has been 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 Čerenkov 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 testing in physiology/biology===
Heavy water is employed as part of a mixture with H<sub>2</sub><sup>18</sup>O for a common and safe test of mean metabolic rate in humans and animals undergoing their normal activities. This metabolic test is usually called the [[doubly-labeled water test]].

===Space-based non-toxic cooling systems===
Heavy water (D<sub>2</sub>O) has a similar high heat of fusion to regular water, but freezes at a slightly higher temperature.  It has been proposed as a non-toxic heatsink for space based cooling applications, where D<sub>2</sub>O ice acts as a heatsink to remove water vapor in air, but without danger that the water vapor will freeze to water-ice, because D<sub>2</sub>O ice maintains temperatures too high for this to occur. See {{US patent|5246061}}. Such a system has not yet been tested.

===Tritium production===
[[Tritium]] is an important material in [[nuclear weapon design]] for [[boosted fission weapon]]s and initiators, and also has civilian industrial applications. Some is created in [[heavy water moderated reactor]]s when deuterium captures a neutron.  This reaction has a small [[Neutron cross-section|cross-section]] and produces only small amounts of tritium, although enough so that cleaning tritium from the moderator may be desirable after several years to reduce the risk of tritium escape and radiation exposure.

Production of large amounts 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 tritium production from [[lithium-6]] (the present method of tritium production), where only chemical separation is needed.

Deuterium's absorption cross section for [[thermal neutron]]s is .52 milli[[barn (unit)|barn]]s, while [[oxygen-16]]'s is .19 millibarns and [[oxygen-17]]'s  is .24 barn. <sup>17</sup>O makes up .038% of natural [[oxygen]], which has an overall absorption cross section of .28 millibarns. Therefore in D<sub>2</sub>O with natural oxygen, 21% of [[neutron capture]]s are on oxygen, a proportion that may rise further as <sup>17</sup>O accumulates from neutron capture on <sup>16</sup>O. Also, <sup>17</sup>O emits an [[alpha particle]] on capture, producing radioactive [[carbon-14]].

==See also==
{{portalpar|Water|Drinking water.jpg}}
* [[Norwegian heavy water sabotage]]
* [[Cold fusion]]
* [[Vienna Standard Mean Ocean Water]]
* [[Deuterium]]

==References==
{{reflist|2}}

== External links ==
*[http://twt.mpei.ac.ru/TTHB/HEDH/PropertiesLiquidHeavyWater.html - Thermodynamic Properties of liquid heavy water]
*[http://www.fas.org/nuke/intro/nuke/heavy.htm Federation of American Scientists article] on the production of heavy water
*[http://www.cns-snc.ca/Bulletin/A_Miller_Heavy_Water.pdf Heavy Water: A Manufacturer’s Guide for the Hydrogen Century] (PDF)
*[http://www.straightdope.com/mailbag/mheavywater.html Straight Dope Staff Report: Is "heavy water" dangerous?]
*[http://alsos.wlu.edu/qsearch.aspx?browse=science/Heavy+Water Annotated bibliography for heavy water from the Alsos Digital Library for Nuclear Issues]
*[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]

[[Category:Forms of water]]
[[Category:Nuclear materials]]
[[Category:Neutron moderators]]

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