The Release of Technetium from Defense Waste Processing Facility Glasses

Abstract

AbstractLaboratory tests are being conducted using two radionuclide-doped Defense Waste Processing Facility (DWPF) glasses (referred to as SRL 131A and SRL 202A) to characterize the effects of the glass surface area/solution volume (SN) ratio on the release and disposition of Tc and several actinide elements. Tests are being conducted at 90°C in a tuff ground water solution at S/V ratios of 10, 2000, and 20,000 m−1 and have been completed through 1822 days. The formation of certain alteration phases in tests at 2000 and 20,000 m−1 results in an increase in the dissolution rates of both glasses. The release of Tc parallels that of B and Na under most test conditions and its release increases when alteration phases form. However, in tests with SRL 202A glass at 20,000 m−1, the Tc concentration in solution decreases coincidentally with an increase in the nitrite/nitrate ratio that indicates a decrease in the solution Eh. This may have occurred due to radiolysis, glass dissolution, the formation of alteration phases, or vessel interactions. Technetium that was reduced from Tc(VII) to Tc(IV) may have precipitated, though the amount of Tc was too low to detect any Tc-bearing phases. These results show the importance of conducting long-term tests with radioactive glasses to characterize the behavior of radionuclides, rather than relying on the observed behavior of nonradioactive surrogates.