Tc-99 and Cs-137 Volatility from the DWPF Production Melter During Vitrification of the First Macrobatch of HLW Sludge at the Savannah River Site

Abstract

Technetium-99 and cesium-137 are two radionuclides in high level waste (HLW) that can volatilize from high temperature melters during the immobilization of the HLW into a borosilicate glass. At Savannah River Site (SRS) the authors have obtained data that indicate that this volatilization is small from the full scale production melter in the Defense Waste Processing Facility (DWPF). These data were obtained during the vitrification of the first HLW macrobatch at SRS. This campaign lasted approximately 2.5 years and produced approximately 9 hundred metric tons of glass from approximately 1.6 million liters of HLW. Losses of Tc-99 and Cs-137 were determined by comparing their measured concentrations in the glass with their respective predicted concentrations based on the composition of the HLW being vitrified. For three glass samples taken during the campaign, the measured and predicted concentrations agreed within 7 percent or better indicating a small loss of either radionuclide. The DWPF melter operates with a cold cap on the surface of the melt. This cold cap could enhance the radionuclide retention, especially Tc-99.