[en] Methods are being developed to immobilize Savannah River Plant (SRP) wastes in high-integrity glass forms. The waste forms will be suitable for storage in an on-site facility or for shipment to an off-site repository. Alkaline wastes produced in SRP separations plants are currently stored in large, carbon-steel tanks. These wastes consist of a water-soluble fraction (salt cake and supernatant liquor) and an insoluble sludge. The water-soluble fraction contains most of the ¹³⁷Cs and the insoluble sludge contains most of the ⁹⁰Sr, waste actinides, and other fission products. ⁹⁰Sr and ¹³⁷Cs are the most hazardous radionuclides in aged waste. A conceptual solidification process has been developed from laboratory tests with both actual and simulated waste. Engineering design studies are in progress. First, wastes are removed as a slurry from the waste tanks. The sludge is separated from the supernate, and then ¹³⁷Cs is removed from the clarified supernate by ion exchange. The resulting decontaminated supernate is evaporated to a salt for bulk storage. In the second part of the process, ¹³⁷Cs is mixed with sludge and the mixture is calcined and then solidified in borosilicate glass. Off-gas from the calciner and glass melter is treated to ensure that no hazardous materials are released to the atmosphere