Abstract: A method for sequestering radioactive waste materials against dissolution and migration into the biosphere during prolonged storage is disclosed. The method comprises incorporating the waste materials as oxides into a mass of molten glass, and subsequently casting the homogeneous molten mass in an inert chemically durable glass container supported by a mold. The container is then sealed and permitted to cool, thereby forming a solid mass having an outer layer or cladding of non-radioactive glass. The glass used for the container preferably is a leach resistant soda-lime-alumina-silica glass similar to conventional bottle glass, and the coefficient of expansion thereof should be sufficiently close to that of the contents to avoid excessive stress at the interface upon cooling.