A reactor core is the central part of a nuclear reactor where nuclear fission occurs. It contains fuel rods, typically made of enriched uranium or plutonium, which undergo a reaction to produce heat. This heat is used to generate steam, which drives turbines to produce electricity. The core is surrounded by a containment structure to prevent the release of radiation. Control rods, made of materials like boron or cadmium, are inserted or removed to regulate the fission process and maintain safety. Proper cooling systems are also essential to remove excess heat and ensure the reactor operates safely and efficiently.