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Title: Reactions during melting of low-activity waste glasses and their effects on the retention of rhenium as a surrogate for technetium-99

Volatile loss of radioactive 99Tc to offgas is a concern with processing the low-activity waste (LAW) at Hanford site. We investigated the partitioning and incorporation of Re (a nonradioactive surrogate for 99Tc) into the glass melt during crucible melting of two simulated LAW feeds that resulted in a large difference in 99mTc/Re retention in glass from the small-scale melter tests. Each feed was prepared from a simulated liquid LAW and chemical and mineral additives (boric acid, silica sand, etc.). The as-mixed slurry feeds were dried at 105°C and heated to 600–1100°C at 5 K/min. The dried feeds and heat treated samples were leached with deionized water for 10 min at room temperature followed by 24-h leaching at 80°C. Chemical compositions of the resulting solutions and insoluble solids were analyzed. Volume expansion measurement and X-ray diffraction were performed on dried feeds and heat treated samples to characterize the progress of feed-to-glass conversion reactions. It was found that the incorporation of Re into glass melt virtually completed during the major feed-to-glass conversion reactions were going on at ≤ 700°C. The present results suggest that the different composition of the salt phase is responsible for the large difference in Re incorporation into glassmore » melt during early stages of glass melting at ≤ 700°C. Additional studies with modified and simplified feeds are underway to understand the details on how the different salt composition affects the Re incorporation.« less
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Resource Type:
Journal Article
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Journal Name: Journal of Non-crystalline Solids, 425:28-45
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
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Country of Publication:
United States
low-activity waste; borosilicate glass; technetium; rhenium; vitrification; retention, volatilization