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3.66: Nuclear Fusion

Difficulty Level: At Grade Created by: CK-12
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What causes the sun to glow so brightly? The answer is nuclear fusion. Nuclear fusion is a type of nuclear reaction, and it releases a huge amount of energy.

What Is Nuclear Fusion?

In nuclear fusion, two or more small nuclei combine to form a single, larger nucleus. You can see an example in the Figure below. In this example, nuclei of two hydrogen isotopes (tritium and deuterium) fuse to form a helium nucleus. A neutron and a tremendous amount of energy are also released.  

Nuclear Fusion

The Power of Stars

Nuclear fusion of hydrogen to form helium occurs naturally in the sun and other stars. It takes place only at extremely high temperatures. That’s because a great deal of energy is needed to overcome the force of repulsion between the positively charged nuclei. The sun’s energy comes from fusion in its core, shown in the Figure below. In the core, temperatures reach millions of degrees Kelvin. The video at the following URL relates nuclear fusion to energy and high temperatures in the sun.

http://www.youtube.com/watch?v=nCXx1yCg6dY

The Sun

Q: Why doesn’t nuclear fusion occur naturally on Earth?

A: Nuclear fusion doesn’t occur naturally on Earth because it requires temperatures far higher than Earth temperatures.

Using Nuclear Fusion

Scientists are searching for ways to create controlled nuclear fusion reactions on Earth. Their goal is develop nuclear fusion power plants, where the energy from fusion of hydrogen nuclei can be converted to electricity. You can see how this might work in the Figure below. In the thermonuclear reactor, radiation from fusion is used to heat water and produce steam. The steam can then be used to turn a turbine and generate electricity.

The use of nuclear fusion for energy has several pros. Unlike nuclear fission, which involves dangerous radioactive elements, nuclear fusion involves just hydrogen and helium. These elements are harmless. Hydrogen is also very plentiful. There is a huge amount of hydrogen in ocean water. The hydrogen in just a gallon of water could produce as much energy by nuclear fusion as burning 1,140 liters (300 gallons) of gasoline! The hydrogen in the oceans would generate enough energy to supply all the world’s people for a very long time.

Unfortunately, using energy from nuclear fusion is far from a reality. Scientists are a long way from developing the necessary technology. One problem is raising temperatures high enough for fusion to take place. Another problem is that matter this hot exists only in the plasma state. There are no known materials that can contain plasma, although a magnet might be able to do it. That’s because plasma consists of ions and responds to magnetism. You can learn more about research on nuclear fusion at the URL below.

http://www.youtube.com/watch?v=3C5hFQeZCT4&feature=related

Summary

  • In nuclear fusion, two or more small nuclei combine to form a single larger nucleus, a neutron, and a tremendous amount of energy.
  • Nuclear fusion of hydrogen to form helium occurs naturally in the sun and other stars. It takes place only at extremely high temperatures.
  • Scientists are searching for ways to create controlled nuclear fusion reactions in order to produce safe nuclear power. Fusion involves only harmless, plentiful elements but requires extremely high temperatures.

Vocabulary

  • nuclear fusion: Fusing of two or more small nuclei to form a single, larger nucleus.

Practice

Watch the video about nuclear fusion at the following URL, and then answer the questions below.

http://www.youtube.com/watch?v=pusKlK1L5To

  1. On Earth, we use energy from the sun for several purposes. List three uses of solar energy.
  2. The sun’s energy comes from nuclear fusion. Explain why nuclear fusion releases energy.
  3. In what form is the energy of nuclear fusion released? How does this energy reach Earth?

Review

  1. What is nuclear fusion?
  2. Where does nuclear fusion occur naturally? Why does it occur only at extremely high temperatures?
  3. Nuclear fusion results in a huge release of energy, yet it doesn’t involve the use of dangerous radioactive elements. Why isn’t it used to produce power?

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    Vocabulary

    nuclear fusion

    Fusing of two or more small nuclei to form a single, larger nucleus.

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    Difficulty Level:
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    Date Created:
    Nov 14, 2012
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    Sep 13, 2016
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