The heat produced it used to evaporate water which turns turbines on a generator.
Steam from the heat of the reactor.
Electrical energy
A power plant generator
If you mean energy produced by nuclear reactors, then "heat" and "light" would be the answers (Just think of the sun)
the controlled release of nuclear energy in a reactor is accomplished
A car engine, a coal or petroleum power plant, a nuclear reactor.
You could for instance convert the nuclear energy to mechanical or electrical energy and use it to pump water up into a high reservoir, where it will have potential energy.
The latest PWR designs can produce 1600MW electrical from one reactor.
An artificial nuclear reactor is a nuclear reactor that is created by man to utilize a nuclear reaction for energy, as opposed to natural nuclear reactors.
You can transform thermal energy to electrical energy in a power plant, chemical energy to mechanical energy in an internal combustion engine, or nuclear energy into thermal energy in a nuclear reactor. These are just three examples.
An Ark reactor as currently describe in comic is very much like a Nuclear Fuel Cell. Possibly convert energy from Nuclear reaction to power. Possibly a plasma nuclear fusion reactor. I believe in the future it could be made. See the link and compare the similarity of fusion reactor and Ark reactor.
In the core.