How is Heavy Water Used in Nuclear Power Plants?

Nuclear power plants rely on nuclear reactions to produce the heat necessary to generate electricity. One type of nuclear reaction that can occur is called nuclear fission, which requires a specific type of fuel known as enriched uranium. However, enriched uranium is not the only fuel that can be used in nuclear reactors. Another option is to use natural uranium in conjunction with heavy water. But what exactly is heavy water and how is it used in nuclear power plants?

What is Heavy Water?

Heavy water has a similar chemical composition to regular water, with two hydrogen atoms and one oxygen atom. The difference is in the hydrogen atoms themselves. In regular water, each hydrogen atom contains one proton and one electron. In heavy water, each hydrogen atom contains one proton and one neutron. This makes the molecule heavier, hence the name "heavy water."

Heavy water is also known as deuterium oxide, since it contains a form of hydrogen called deuterium. While regular hydrogen makes up over 99% of the hydrogen on Earth, deuterium is a rare isotope that makes up only about 0.015% of natural hydrogen.

How is Heavy Water Produced?

Heavy water is produced through a process called isotopic exchange. This involves taking regular water and subjecting it to a reaction with hydrogen sulfide gas. The reaction causes the oxygen atoms in the water molecules to swap places with sulfur atoms, resulting in a new molecule called hydrogen sulfite. This molecule is then reacted with hydrogen gas, which causes the sulfur atoms to return to their original position and the hydrogen atoms to replace the oxygen atoms. The end result is heavy water.

Another method for producing heavy water involves distilling regular water and selectively removing the molecules that contain deuterium. This method is more expensive and less efficient than isotopic exchange, but it is still used in some situations.

How is Heavy Water Used in Nuclear Power Plants?

In nuclear power plants that use heavy water, the heavy water is used as a moderator. A moderator is a substance that slows down the neutrons produced during fission reactions, which makes them more likely to collide with other uranium atoms and continue the chain reaction. Without a moderator, the neutrons would move too quickly and escape the uranium fuel, causing the reaction to stop.

Heavy water is an effective moderator because its heavy hydrogen atoms slow down neutrons more effectively than regular hydrogen atoms. Additionally, heavy water does not absorb neutrons as readily as other moderators like graphite, which can be important for nuclear reactors that use natural uranium fuel.

Conclusion

While heavy water is not as commonly used as enriched uranium in nuclear power plants, it is still an important component of some reactors. Its unique properties as a moderator make it an effective alternative to other materials, and it can be produced using a variety of methods. Overall, heavy water is another example of the diverse and complicated technology used to generate electricity through nuclear power.