Massive amounts of destructive energy are released when a nuclear fission bomb exploded. Where does that energy come from?

Nuclear fission : it a process in which large unstable nucleus splits into stable smaller stable nuclei. During this spilling large amount of energy is released.

The massive amounts of destructive energy is released during nuclear bomb explosion. The source of this energy, is the splitting of larger nucleus into smaller nuclei which releases large amount of energy.

chain reaction occurs when uranium atoms split