In school, I remember chemistry being easy to comprehend. Not to oversimplify the science but we mixed chemicals which we could smell and see and voila! You get some totally different compound with hopefully some fire. After all, what is chemistry class without fire.
Chemistry reactions result as elections change positions with other electrons with other atoms or molecules. Physics reactions dive deeper. The world of physics is much harder to conceptualize because the reactions that define this science occur at the level of the atom. In broad terms (not entirely accurate), an atom looks something like this: Electrons orbiting around a nucleus of protons and electrons.
What is the particle that is responsible for nuclear reactions? It is called the NEUTRON. It resides inside the nucleus. It wasn't discovered in 1932. By 1942, it was used in the first nuclear chain reaction. Neutrons are very small. You could fit more than 66 TRILLION NEUTRONS end to end on a meter stick.
The force that holds this ultra-small particle in the center contains billions and billions of times MORE POTENTIAL ENERGY than everyday chemical reactions. Its even stronger than GRAVITY! This is what makes nuclear power so attractive.
Our mind has a difficult time quantifying these changes because these reactions don't occur in our macroscopic world we observe each day. it isn't until the byproducts of these reactions become a danger in our world we live in. Unfortunately, the potential meltdown of the nuclear reactors in Japan and the explosions on the news have provided the framework for observation and criticism for all of us not familiar with nuclear technology.
The fuel that is used in nuclear reactions, believe it or not, occurs in nature. Uranium is a naturally occurring radioactive element. It exists in several types. Uranium 235 and 238. The numbers indicate the number of NEUTRONS IN THE NUCLEUS.
In a nuclear reaction, the uranium is hit with a neutron. The collision create tremendous amounts of energy, other elements (Krypton-92 and Barium-141) and MORE NEUTRONS which feed the reaction further.
Remember that the amount of Uranium in a power plant is small compared to necessary amount of coal needed to produce the same amount of energy. One pound of uranium will provide the same amount of energy as burning 1,500 tons of coal. This is why a conversion to nuclear power has been desirable. Its very efficient.