Nuclear Fission: Fragmentation is a word that refers to the splitting or disintegration of something into smaller pieces. Nuclear fission in this context refers to the split or fission of a larger parent atom into two or more daughter atoms. Technically speaking, these small atoms are light in weight. A large amount of energy is released when the nuclear fission process breaks down, proving that it is an exothermic process.
Nuclear Fusion: The merging of two or more objects is called a "fuse". The process by which two or more atoms combine to form a larger atom is called nuclear fusion. Since it takes energy to fuse two atoms, the nuclear fusion process is endothermic. Consider connecting or fusing the two train bogies using a magnet.
Therefore,
When atoms are separated, they release energy, whereas when atoms are linked, they release energy. The fusion reaction produces more energy than the fission reaction.
Fusion, unlike fission, does not produce hazardous long-term radioactive waste as a byproduct. Fusion requires more energy to complete than fission.