Nuclear energy is energy that comes from a nucleus, the core of an atom. Atoms are particles that make up every object; and there exists a lot of energy (binding forces) which holds these atoms together. Nuclear energy can be used to make elecricity, but for this to happen the energy has to be released from atoms.
There are two ways energy can be released from an atom: nuclear fusion or nuclear fission (which are exact opposites). Nuclear fusion means that atoms combine to fuse into a larger atom (which is how the sun produces energy). Nuclear fission means that the atom splits into smaller atoms releasing energy.
Nuclear power plants use nuclear fission to create electricity. The fuel that nuclear power plants use for nuclear fission is uranium. Unlike solar power and wind energy, uranium is a non-renewable resource. Inside the nuclear reactor, where fission takes place, a particle called a neutron hits the uranium atom, which then splits the uranium atom releasing a great amount of energy as heat and radiation.
In a boiling-water reactor (BWR) heat is used to boil water, produce steam and the steam then turns a turbine. So nuclear power plants use the heat during the fission process to produce electricity. In a pressurized-water reactor (PWR) the water passing through the reactor is not transformed to steam as it is kept under intense pressure. It remains liquid. The PWR has a steam generator on the side and channels its radioactive water to this steam generator.
The uranium fuel produced is formed into ceramic pellets the size of a capsule but each one produces the same amount of energy as 675 litres of oil. Nuclear energy is highly efficient but also has highly toxic waste as a byproduct, however nuclear power plants do not release any CO2 emissions.
Although nuclear energy provides 30% of electricity in Europe, the general movement against nuclear comes from a fear of a possible nuclear accident (such as Chernobyl), nuclear radiation, nuclear proliferation and nuclear waste, plus destruction of the environment through mining of uranium. The anti-nuclear lobby would much prefer more focus on solar power and wind energy to address the world's current and future energy needs