Leach rate studies on glass containing actual radioactive waste

Borosilicate glass containing radioactive wastes from the Savannah River Plant have been leached for 900 days. The International Standards Organization's (ISO) static leach test procedure was used on glass buttons in various leachants. Leach rates based on 90Sr and 137Cs analyses were similar: 2 x 10-8 to 3 x 10-8 g/(cm2)(d) in distilled water, 1 x 10-8 to 3 x 10-7 g/(cm2)(d) in pH 7 buffer, 3 x 10-7 to 7 x 10-7 g/(cm2)(d) in pH 9 buffer, and 7 x 10-6 to 8 x 10-5 g/(cm2)(d) in pH 4 buffer. Rates based on Pu analyses were the same as above in distilled water and pH 9 buffer, but were lower by an order of magnitude in pH 4 and pH 7 buffers. Almost all leach rates remained constant between 200 and 900 days of leaching. Increasing the concentration of the buffering agents had no effect on the leach rates at pH 7 (phosphate) and pH 9 (carbonate), but dramatically increased the rates at pH 4 (acetate). Leach rates did not differ significantly between high aluminum and high iron waste glasses