As of 2015, there are more than 400 nuclear power plants in operation around the world. Public opinion on the plants is mixed, with some decrying them as dangerous and citing the Chernobyl and Fukushima disasters. Others see them as a promising symbol of a future that runs on clean, efficient energy. The plants produce electricity through a process called fission. Inside a reactor, elements such as uranium-235 split into smaller atoms during fission, releasing energy that heats nearby water and turns it into steam. The steam causes a turbine connected to an electric generator to rotate, thereby producing electricity.