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Defiant of a deadline presented by the West, Iran inaugurated a heavy water plant on August 26, 2006. The plant will supply heavy water to a nuclear reactor that will be completed in 2009. Iran has once again stated that its nuclear program poses no threat to any country. The West, however, suspects the facility will be used in the production of nuclear warheads.
Heavy Water
Heavy water is a term used to refer to deuterium oxide or D2O. Deuterium is an isotope of hydrogen. While hydrogen contains only one proton in its nucleus, deuterium contains an additional neutron as well. Deuterium oxide is very similar to light water (H2O); the only difference is that the two hydrogen atoms in the heavy water molecule have an extra neutron in them. The substitution alters the bond energy in the hydrogen-oxygen bond. This leads to alteration of the physical, chemical, and biological properties of heavy water when compared to light water.
Deuterium was first discovered in 1931 by Harold Urey at Colombia University. The discovery was later supplemented in 1932 by the discovery of the extra neutron by James Chadwick from Cambridge. Ever since then, scientists have been interested in deuterium because of its special properties. Research on its application in different fields has captured the attention of the scientific community.
Heavy water is not radioactive, and it occurs naturally in water. It is usually found in water at a proportion of about one molecule in 5,000. When talking about producing heavy water, this actually refers to extraction of the heavy water from the vast quantity of water. It may be by fractional distillation (similar to the process used in crude oil distillation) or by electrolysis with no nuclear transfer needed. These methods can be expensive, however, and require huge amounts of energy. The cheaper option is by using the chemical method. The most important chemical method for producing heavy water is the Girdler Sulfide process, developed by the US.
Use in Nuclear Reactors
There are normally two types of nuclear reactors. The first type runs on enriched uranium and is moderated by normal water. The second type uses natural uranium but requires heavy water as a moderator. Normal water cannot be used with natural uranium because water tends to absorb neutrons, making it possible to use it only with enriched uranium.
Heavy water is one of the two principal moderators that allow a nuclear reactor to operate with natural uranium as fuel. The other moderator is reactor-grade graphite (graphite containing less than 5 parts per million boron and with a density exceeding 1.50 gm/cm3).
Heavy water production reactors can therefore be used to transform natural uranium into bomb-grade plutonium. This is done without the need of enrichment facilities and all the related sophisticated infrastructure. Several countries have used heavy water production reactors for this purpose, including India, Pakistan, Israel, and the US. It is this use that has the West worried about Iran's heavy water reactor. They allege that the new nuclear reactor being built can produce enough plutonium for one nuclear bomb annually, using heavy water for moderation.
Heavy water can also be used to produce tritium, which is another hydrogen isotope but with two extra neutrons. Tritium is radioactive and is an important element in thermonuclear weapons.
Pharmaceutical Uses
Aside from the production of weapons of mass destruction (WMD), heavy water has several pharmaceutical uses.
Deuterium oxide's low toxicity towards mammals in general allows it several medicinal uses. Perhaps the most widespread use for heavy water is for measuring water spaces in humans and other animals to determine cases of water retention. Another use is for measuring the metabolic rate of an organism over a period of time. This is done by a method called the doubly-labeled water.
Heavy water is also used with cancer patients. It can be used both in diagnosis and treatment where it can decrease genotoxicity, which is the DNA damage resulting from certain anticancer drugs.
Deuterium is also used in the diagnosis of AIDS, and is used in research to determine the metabolism of drugs and toxic substances inside humans and animal bodies.
Toxicity
Experiments on rats, cats, and dogs show that toxicity usually starts at a degree of 25 percent deuteration. This manifests in the form of sterility in both sexes. At higher concentrations of 90 percent, it causes death in fish and flatworms. However, toxicity in humans is so unlikely that it is practically disregarded. This is because very large amounts of pure heavy water would need to be ingested before toxicity levels above 25 percent are reached.
Commercial Use
Several countries have heavy water production plants. The biggest and most important one in the world is the Bruce Heavy Water Plant in Ontario, Canada, operated by Ontario Hydro. The Ontario Hydro is the biggest commercial producer of heavy water in the world. India is the world's second largest producer of heavy water through its Heavy Water Board, but production has recently been troubled with accidents.
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