A nuclear fusion reaction could produce a virtually limitless and clean source of energy. This occurs when two light atomic nuclei fuse to form a heavier nucleus. This releases a large amount of energy.
You probably mean nuclear fusion, using heavy water found in the oceans. This would not be absolutely limitless, ie not strictly renewable, but as far as human existence goes it would be virtually limitless
Nuclear fission
From the nuclear reaction of burning hydrogen!
A controlled nuclear chain reaction produces heat, driving steam turbines to produce energy.
We use nuclear fission in nuclear reactors to tap nuclear energy.
Probably Rutherford.
nuclear fusion
It is true that nuclear reaction produce huge amounts of energy by transforming tiny amounts of matter.
Nuclear Fusion
Nuclear reaction inside the Sun is fusing of Hydrogen to Helium and release out thermal energy.
All the nuclear fissions produce smaller elements from the larger element and few neutrons so that the fission reaction is continuously carried out.
A nuclear reactor contains a nuclear reaction, provides support for the control mechanisms for the reaction, and provides for the transfer of heat to machinery that will use it to produce electric power.