The reactor core, where uranium or plutonium is converted to lighter elements with the production of much heat, heats gas or water that is used to cool the container. That "coolant" gas or water is recirculated and not released to the environment. The heated material is used to produce steam, and the steam passes through a turbine that drives an electric generator. The generator works the same way as a generator at a fuel-burning power plant or a hydrolectric dam.
