Abstract: Radioactive waste materials are converted into solid form by mixing the radioactive waste with a novel polymeric formulation which, when solidified, forms a solid, substantially rigid matrix that contains and entraps the radioactive waste. The polymeric formulation comprises, in certain significant proportions by weight, urea-formaldehyde; methylated urea-formaldehyde; urea and a plasticizer. A defoaming agent may also be incorporated into the polymeric composition. In the practice of the invention, radioactive waste, in the form of a liquid or slurry, is mixed with the polymeric formulation, with this mixture then being treated with an acidic catalyzing agent, such as sulfuric acid. This mixture is then preferably passed to a disposable container so that, upon solidification, the radioactive waste, entrapped within the matrix formed by the polymeric formulation, may be safely and effectively stored or disposed of.