Chemical fuels, such as oil or methane, release energy when the atoms in their molecules are rearranged into a lower energy configuration. The energies involved are those of molecular binding and are of the order of tens of MJ/kg. When the components of an atomic nucleus (protons and neutrons) are arranged into lower energy configurations, then the energy released is orders of magnitude larger (hundreds of TJ/kg) because of the much larger intra-atomic binding energies.
The internal structure of atoms can be changed in different ways1:
1. An atomic nucleus can be bombarded with a neutron, absorbing it. A different atom emerges.
2. An atom can spontaneously change by emitting either electrons (beta-rays) ...