Nuclear reactors are facilities that initiate and control nuclear chain reactions to generate energy. They are primarily used in nuclear power plants to produce electricity, harnessing the immense energy released from nuclear fission, where atomic nuclei split apart. This process is highly efficient and can produce large amounts of energy from small amounts of fuel, typically uranium or plutonium. In addition to electricity generation, nuclear reactors are also used in research and medical applications. For instance, they can produce isotopes for medical imaging and cancer treatment. Safety measures and regulations are crucial in reactor design to prevent accidents and ensure the protection of both people and the environment.