what device in a nuclear power plant creates nuclear energy?

Answer 1

The origin of the energy is the reactor core. Control rods are pulled out of the core to start the reactor, and a controlled chain reaction begins and is maintained. Neutrons released in fissions create other fissions to keep the chain alive. The fissions release energy, much of which is heat energy. The heat is transferred out of the core into the reactor coolant. The coolant transfers the heat into steam generators, and the heat creates steam which is then piped to steam turbines. The turbines drive generators to create electricity, which is then put on the power grid.