7 Fission
Quite simply, fission is the splitting of the atom by a neutron to release energy. Some atoms split more readily than others.
Splitting uranium
[latex]^{1}_{0}n + ^{235}_{92}U \rightarrow ^{92}_{36}Kr + ^{141}_{56}Ba + ^{1}_{0}n + ^{1}_{0}n + ^{1}_{0}n[/latex]
Uranium is widely used as nuclear fuel for fission, but other TRUs can be split as well. Actually, any atom can be split, but the selection of the atom should be one such that the most energy could be released.
A straightforward calculation of the Q value shows that [latex]Q = 173.3 \; MeV[/latex]. In contrast, burning a carbon atom yields [latex]4 \; eV[/latex].
In the fission reaction for [latex]^{235}_{92}U[/latex] above, two fission products and three neutrons are released. This is not the same exact reaction every time, but fission product yields for a given atom are readily obtained.
Similarly, on average 2 to 3 neutrons are released. Again, the neutrons emitted per fission ([latex]\nu[/latex]) is also readily obtained.
This is the whole point of fission. With additional neutrons produced, a chain reaction of fission can be controlled, releasing large amounts of energy in order to generate electricity.
Additional notes