Answer: These are called as nuclear chain reactions.
Explanation: Nuclear Fission reactions are the reactions in which one heavier nuclei produces two lighter daughter nuclei.
Nuclear chain reactions are defined as the chemical reactions when one neutron released in a fission reaction produces another fission reactions in other nucleus. The other nucleus again releases neutrons and a chain of reactions is formed.
These reactions are generally uncontrollable.
Hence, The continuous release of nuclear energy caused when on fission reaction triggers more nuclear reactions is a nuclear chain reaction.