Final answer:
Nuclear power plants harness energy from the process of fission, which involves splitting the nucleus of a heavy atom. This releases a large amount of energy that is used to generate electricity.
Step-by-step explanation:
Nuclear power plants harness energy from the process of fission. This involves splitting the nucleus of a heavy atom, such as uranium or plutonium, into two smaller nuclei, releasing a large amount of energy in the process. This energy is then used to heat water and produce steam, which drives a turbine and generates electricity.