Nuclear power plants utilize radioactive materials and the process of nuclear fission to generate the heat and steam needed to run electrical generators and produce electricity. Because nuclear power doesn't cause the air pollution associated with the burning of coal or petroleum products, this means of generating power is considered a viable alternative energy source. However, the toxic nature of the byproducts produced by the fission process creates serious problems of its own. No method of safely disposing of this toxic waste has been found, and the volatile nature of the fission reaction can lead to a meltdown of the reactor core if the reaction is not properly controlled. Because of these problems, the future of nuclear power is uncertain.