Two infamous nuclear disasters happened in Pennsylvania in 1979 and Ukraine in 1986. Today, nuclear reactors are:

Atoms are tiny building blocks that make up all matter in the Universe. Atoms may be tiny, but they hold an extraordinary amount of energy in their core, or nucleus. This energy can be released when atoms are split apart, producing nuclear power. Nuclear power plants split atoms of a certain kind of uranium to release huge amounts of heat. In turn, this heat drives a generator that produces electricity.
Two infamous nuclear disasters happened in Pennsylvania in 1979 and Ukraine in 1986. Today, nuclear reactors are:
just as dangerous
built only in remote areas
relatively safe
Nuclear reactors today are more closely monitored and use safer technologies. However, reactors do produce dangerous radioactive waste that must be safely contained for thousands of years.
Nuclear reactors split apart atoms of a certain kind of uranium to release energy. This process is called:
fission
friction
fusion
In nuclear fission, atoms are split apart to form smaller atoms. The opposite is fusion, in which atoms are combined to form larger atoms. Both processes release energy. Nuclear power plants use fission.
Nuclear reactors release large amounts of carbon dioxide and other air pollutants.
Nuclear reactors don't release any carbon dioxide or other air pollutant. But, the mining and processing of uranium do cause pollution.
Since uranium is a common metal found in rocks, nuclear plants have an unlimited amount of fuel.
Uranium is a common metal, but nuclear reactors can use only a specific kind called uranium-235. It is quite rare and could one day run out.
Definition: the energy released by splitting apart an atom
Carbon Dioxide Emissions: none (except during uranium mining and processing)
Cost: expensive (vs. other energy sources)
Location: only in a few countries (including the U.S.), as permitted by international agreements
Current Use: almost 15% of the world's energy
Cool Fact: A single pellet of uranium can generate as much electricity as 150 gallons of oil!