Nuclear fission is essentially the opposite of nuclear fusion. Here, a single nucleus divides into two smaller nuclei. In the case of heavy atoms, this is often accompanied by the release of heat. For example, the radioactive decay of uranium-235 can be used to generate the heat used to drive turbines to generate electricity in nuclear power plants. The use of nuclear fission to harness energy for use by humans is typically considered the much more viable choice (as opposed to nuclear fusion).