Chapter 13: Nuclear Energy – Fission and Fusion Another major form of energy is nuclear energy, the energy that is trapped inside each atom. One of the laws of the universe is that matter and energy can't be created nor destroyed

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Chapter 13: Nuclear Energy – Fission and Fusion

Another major form of energy is nuclear energy, the energy that is trapped inside each atom. One of the laws of the universe is that matter and energy can't be created nor destroyed. But they can be changed in form.

Matter can be changed into energy. The world's most famous scientist, Albert Einstein, created the mathematical formula that explains this. It is:

This equation says: formula

E [energy] equals m [mass] times c2 [c stands for the velocity or the speed of light. c2 means c times c, or the speed of light raised to the second power — or c-squared.] depiction of atom

Scientists used Einstein's famous equation as the key to unlock atomic energy and also create atomic bombs.

The ancient Greeks said the smallest part of nature is an atom. But they did not know 2,000 years ago about nature's even smaller parts.

As we learned in the last unit, atoms are made up of smaller particles -- a nucleus of protons and neutrons, surrounded by electrons which zoom around the nucleus in specific electron clouds. Nuclear Fission

An atom's nucleus can be split apart. When this is done, a tremendous amount of energy is released. The energy is both heat and light energy. Einstein said that a very small amount of matter contains a very LARGE amount of energy. This energy, when let out slowly, can be harnessed to generate electricity. When it is let out all at once, it can make a tremendous explosion in an atomic bomb. drawing of fuel rod assembly

A nuclear power plant (like Diablo Canyon Nuclear Plant shown below) uses uranium as a "fuel." Uranium is an element that is dug out of the ground many places around the world. It is processed into tiny pellets that are loaded into very long rods that are put into the power plant's reactor.

The word fission means to split apart. Inside the reactor of an atomic power plant, uranium atoms are split apart in a controlled chain reaction.

In a chain reaction, particles released by the splitting of the atom go off and strike other uranium atoms splitting those. Those particles given off split still other atoms in a chain reaction. In nuclear power plants, control rods are used to keep the splitting regulated so it doesn't go too fast. nuclear power plant 8786550

If the reaction is not controlled, you could have an atomic bomb. But in atomic bombs, almost pure pieces of the element Uranium-235 or Plutonium, of a precise mass and shape, must be brought together and held together, with great force. These conditions are not present in a nuclear reactor.

The reaction also creates radioactive material. This material could hurt people if released, so it is kept in a solid form. The very strong concrete dome in the picture is designed to keep this material inside if an accident happens.

This chain reaction gives off heat energy. This heat energy is used to boil water in the core of the reactor. So, instead of burning a fuel, nuclear power plants use the chain reaction of atoms splitting to change the energy of atoms into heat energy.

This water from around the nuclear core is sent to another section of the power plant. Here, in the heat exchanger, it heats another set of pipes filled with water to make steam. The steam in this second set of pipes turns a turbine to generate electricity. Below is a cross section of the inside of a typical nuclear power plant. nuclear power plant drawing

Power plant drawing courtesy Nuclear Institute Nuclear Fusion

nuclear fusion drawing

Another form of nuclear energy is called fusion. Fusion means joining smaller nuclei (the plural of nucleus) to make a larger nucleus. The sun uses nuclear fusion of hydrogen atoms into helium atoms. This gives off heat and light and other radiation.

In the picture to the right, two types of hydrogen atoms, deuterium and tritium, combine to make a helium atom and an extra particle called a neutron.

Also given off in this fusion reaction is energy! Thanks to the University of California, Berkeley for the picture.

Scientists have been working on controlling nuclear fusion for a long time, trying to make a fusion reactor to produce electricity. But they have been having trouble learning how to control the reaction in a contained space.

What's better about nuclear fusion is that it creates less radioactive material than fission, and its supply of fuel can last longer than the sun.


Nuclear Fission

Nuclear Fusion


Fission is the splitting of a large atom into two or more smaller ones.

Fusion is the fusing of two or more lighter atoms into a larger one.

Natural occurrence of the process:

Fission reaction does not normally occur in nature.

Fusion occurs in stars, such as the sun.

Byproducts of the reaction:

Fission produces many highly radioactive particles.

Few radioactive particles are produced by fusion reaction, but if a fission "trigger" is used, radioactive particles will result from that.


Critical mass of the substance and high-speed neutrons are required.

High density, high temperature environment is required.

Energy Requirement:

Takes little energy to split two atoms in a fission reaction.

Extremely high energy is required to bring two or more protons close enough that nuclear forces overcome their electrostatic repulsion.

Energy Released:

The energy released by fission is a million times greater than that released in chemical reactions; but lower than the energy released by nuclear fusion.

The energy released by fusion is three to four times greater than the energy released by fission.

Nuclear weapon:

One class of nuclear weapon is a fission bomb, also known as an atomic bomb or atom bomb.

One class of nuclear weapon is the hydrogen bomb, which uses a fission reaction to "trigger" a fusion reaction.

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