Figure 3
Source publication
Corroding waste tanks at select U.S. Department of Energy's nuclear waste facility have leaked highly alkaline tank waste solutions containing radionuclides and other contaminants into subsurface sediments. These tank wastes react with subsurface sediments to form secondary mineral phase(s) (feldspathoids), which may play key role in the transport...
Citations
... Various options have been considered for the immobilization of the Tc removed from off-gas. One is to extract the Tc from the off-gas condensates and add it to HLW melter feed either in the form of pertechnetate or in the form of durable minerals, such as spinel or sodalite [21][22][23]. In this work, we pursued the option of adding potassium perrhenate (a nonradioactive surrogate for pertechnetate) to a HLW melter feed at a relatively high concentration of $1 mass% Re in the glass. ...
We investigated volatilization of rhenium (Re), sulfur, cesium, and iodine during the course of conversion of high-level waste melter feed to glass and compared the results for Re volatilization with those in low-activity waste borosilicate glasses. Whereas Re did not volatilize from high-level waste feed heated at 5 K min-1 until 1000°C, it began to volatilize from low-activity waste borosilicate glass feeds at ∼600°C, a temperature ∼200 °C below the onset temperature of evaporation from pure KReO4. Below 800°C, perrhenate evaporation in low-activity waste melter feeds was enhanced by vigorous foaming and generation of gases from molten salts as they reacted with the glass-forming constituents. At high temperatures, when the glass-forming phase was consolidated, perrhenates were transported to the top surface of glass melt in bubbles, typically together with sulfates and halides. Based on the results of this study (to be considered preliminary at this stage), the high-level waste glass with less foaming and salts appears a promising medium for technetium immobilization.
