A nuclear reactor is a facility that generates energy through a process called nuclear fission. In this process, the nuclei of certain heavy atoms, like uranium or plutonium, are split apart, releasing a large amount of heat. This heat is used to produce steam, which then drives turbines to generate electricity. Nuclear reactors are designed with safety features to control the fission reaction and prevent accidents. They typically include a containment structure to protect against radiation leaks and systems to cool the reactor core. Overall, nuclear reactors play a significant role in providing a stable source of energy for many countries.