Evaluation of glass as a matrix for solidification of Savannah River Plant waste

Laboratory tests using actual sludges collected from Savannah River Plant (SRP) waste tanks were performed to evaluate glass as a waste solidification matrix. Sludge was collected from three SRP waste tanks, washed to remove soluble salts, and then ground to a fine powder. From 25 to 40 wt percent of these sludges was vitrified into a borosilicate glass by melting at 11500C. Substitution of 4 wt percent Li2O for 4 wt percent Na2O in the glass mix allowed higher loading of a high-aluminum sludge. No problems with phase separation were encountered, and all sludge components, except mercury which volatilized, appeared to dissolve completely in the glass melt. Volatilization of radionuclides during melting was 0.3 percent for 137Cs, 2.9 percent for 106Ru, and less than or equal to 0.01 percent for other nuclides. Initial leachabilities of glass products were low: 10-6 to 10-5 g/(cm2-day) for 137 , 90Sr, and alpha activity. Leachabilities decreased to 10-8 to 10-7 g/(cm2- day) in approximately 2 weeks. Heating the glasses at 6000C for 1 month caused devitrification which increased leachability, but durable waste forms still remained. This work showed that vitrification of SRP high-level waste sludges in borosilicate glass is feasible. Further investigation of melting concepts, scale-up, cost, long-term stability, and other factors are planned as a part of the development program for long-term waste management. (auth)