Fission and fusion are both atomic nuclear reactions. Atomic means they involve individual atoms and nuclear means that the reaction is in the nucleus of the atoms. Reaction means that an interaction takes place that causes a change. Nuclear reactions, like all reactions, can take energy or release energy.

The reactions we are most familiar with are chemical reactions. When we burn wood or fossil fuel to release energy we are dealing with a chemical reaction. A chemical reaction is different from a nuclear reaction in the level at which the changes take place. In a chemical reaction molecules are taken apart and put together in a different arrangement. The atoms themselves are unchanged

Nuclear reactions differ from chemical reactions in that they take place at the atomic nuclear level. Atomic nuclei are made up of protons and neutrons. Nuclear reactions change the configuration of the protons and neutrons within the nucleus of the atom. This type of reaction can release much more energy than a chemical reaction.

And, this is is the level where the difference between fission and fusion come in.

Fission is the splitting of atomic nuclei into two or more parts. To help understand the terminology we might consider the source of the word "fission". It comes from the same root as the more familiar word "fissure" which refers to a split in something. Fission involves taking apart the nucleus of an atom.

Fusion is the combining of two or more atomic nuclei into one. The root word for "fusion" is related to the common word "fuse" which means to combine. Fusion involves putting together nuclei of atoms.

Most reactions require an input of energy to occur. To start a chemical reaction we might use a match to start a piece of paper burning. In the case of burning paper, once the reaction is started it releases enough energy to continue the reaction in other parts of the paper and also releases energy in the form of heat and light.

Some chemical reactions occur spontaneously. Many molecules are unstable and will change their molecular structure with little or no input of energy. Some atomic nuclei are also unstable and will undergo fission with little or no input of energy. These are the radioactive elements like uranium that, over time, break down into simpler elements.

The fission reactions which we use to generate energy in nuclear power plants usually require an input of energy to start. The most common reaction is the splitting of the nucleus of specific

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