PS-2.6  Compare fission and fusion (including the basic processes and the fact that both fission and fusion convert a fraction of the mass of interacting particles into energy and release a great amount of energy).
Key Concepts:
Nuclear fission:  chain reaction, critical mass
Nuclear fusion  
Nuclear reactions result in changes in the nucleus of the atom, not in the electron structure as with chemical reactions.  I all nuclear reactions some quantity of mass within the nucleus of the atom is converted into energy. In nuclear fission reactions, large nuclei, such as Uranium nuclei, are split by high speed neutrons. When the nuclei are split some of the mass is converted to various forms of energy. Heat is one common form of energy released form fission reactions, this is why fission Reactions are used in nuclear power plants. In nuclear power plants, the heat released during the fission reaction is used to boil water to produce high pressure steam. The high pressure steam is then used to turn a turbine, which then turns an electric generator to produce electricity. Click HERE and you can see an animation showing how a nuclear power plant works.
A sustained fission reaction, such as those that occur in atom bombs, require that there be enough fissile material to sustain a chain reaction. If there is not enough fissile material the reaction will stop. The quantity of fissile material required to sustain the reaction is called the critical mass.
Fusion Reactions, or more specifically Thermonuclear Fusion Reactions,  are nuclear reactions that fuse small nuclei together to make larger nuclei. During the process extremely small amounts of matter ( mass) are converted into vast quantities of energy, usually in the form heat and light. It is a thermonuclear fusion reaction that fuels the Sun and other stars. In the core of our Sun or other stars, intense gravitational forces squeeze Hydrogen nuclei together to form larger Helium nuclei. Click HERE and you can see an animation of a fusion reaction. A nuclear bomb that uses a fusion reaction is called a hydrogen bomb.
E=MC2 : Energy equals mass times the speed of light squared. The significance of squaring the speed of light (2.99 x 108m/s) is that is increases the energy product of this equation drastically...A tiny bit of matter (mass) can be converted into a tremendous quantity of energy.  The mass of a single m&m candy is 0.88g.  Burning this M&M would release enough energy to bring about 10g of water to a boil. However, IF you could convert the total mass of a single M&M candy into energy E=MC2 = .088kg x (2.99 x 108m/s)2 = 7.9x1013 Joules. That's enough energy to run the average home for about 910 years.  If ALL the mass of 2 M&M's were released as energy it would be enough to put the space Shuttle in orbit. Click HERE and you can hear Einstein explain E=MC2 in his own words.
Click here to see a really nice video on Nuclear energy.