When discussing negotiations with Iran on nuclear weapons, heavy water often is mentioned. What is it, and why is it important?
The element hydrogen has several forms. The form with we are most accustomed is found in the water that we drink (H2O). This is "light" water.
However, another form of hydrogen is in heavy water. This form (isotope) has an extra atomic particle (a neutron), and often is called deuterium. When this heavier hydrogen is linked to oxygen, a different type of water is created. It is called "heavy water" because the hydrogen atom is heavier.
Two types of nuclear reactors are in use today: light-water reactors; and heavy-water reactors.
Light-water reactors require the expensive heavily enriched uranium U-235 discussed in an earlier post. However, heavy-water reactors are able to use the much less expensive and much more readily available uranium U-238.
Moreover, and possibly more important with respect to Iran, heavy-water reactors produce significantly greater quantities of plutonium as a by-product. Why is plutonium a concern?
A nuclear weapon made just using enriched uranium is the type of "simple" atomic bomb developed by the United States and used at Hiroshima. A nuclear weapon made using plutonium is the type of more powerful atomic bomb the United States used at Nagasaki.