Fission and fusion are different types of nuclear reactions in which
energy is released from the high-powered bonds between particles in the
atomic nucleus. The atomic nucleus is most stable when binding energies
between particles are strongest. This occurs with iron and nickel. For
lighter atomic nuclei, energy can be extracted by combining these
nuclei together, a process known as nuclear fusion. For nuclei heavier
than those of iron or nickel, energy can be extracted by splitting them
apart in a process called nuclear fission.
Because the binding force in the atomic nucleus contains enormous
energy, fission and fusion can both provide tons of power, in
principle. However, practical considerations make the exploitation of
nuclear power more difficult than something as simple as starting a
fire. For fission, highly purified feedstock, usually uranium or plutonium isotopes,
must be used. Isotopes are favored because their instability makes them
easier to break apart. The purification of these isotopes is extremely
expensive and requires multimillion-dollar centrifuges.
In fusion, an extremely high threshold energy must be reached to
combine atomic nuclei. In nature, the only place where this occurs is
in the core of a star. The temperature required is in the millions of
degrees. Superheated plasma and the focusing of laser power are two methods to achieve this threshold energy.
Because the matter that serves as the medium of fusion must be so
hot, it must be isolated from surrounding matter using powerful
magnetic fields or inertial containment. This is the principle behind
the Tokamak reactor. Still, fusion requires so much energy that no one has yet built a reactor that produces more than it consumes.
The downsides to fission power include both radioactive byproducts and its association with nuclear weapons and meltdowns. In the last decade or so, nuclear physicistshave developed safer ways of building reactors, including methods for
recycling the radioactive byproducts of fission. These advances have
caused the US government to begin advocating the construction of
nuclear reactors again.