Although atoms are tiny, they hold a massive amount of energy
between the bonds of their nuclei. This energy can be harvested
through what is called nuclear fission, or the splitting of bonds
between atoms. By splitting apart chemical bonds holding the atoms
together chemical energy is released in the form of thermermal
energy or heat. The heat energy released can then be used to
generate electricity throughout the power plant.
Certain isotopes (different forms of an element) of certain elements
can be more easily fissioned and harvested. For example,
Uranium-235, or U-235, is the most common isotope used in nuclear
power plants. Since the uranium atom is quite big in comparison to
others it is relatively easier to go though the process of Fission.
During fission, the U-235 atom will absorb loose neutrons causing
the U-235 to become unstable and split apart into two lighter atoms
called fission products, energy in the form of heat, as well as two
to three more neutrons at high velocity. These new neutrons will
proceed to crash into more atoms causing a chain reaction.