Effect of water vapor and thermal history on nuclear waste feed conversion to glass

Abstract

AbstractWater affects the glass melting process by interacting with the foam layer at the glass melt surface and by influencing the batch conversion reactions. Nuclear waste aqueous slurry feed maintains a high water vapor pressure in the melter atmosphere. To investigate to what extent water vapor affects the foaming during vitrification of nuclear waste in joule‐heated cold‐top melters, a series of feed expansion experiments were performed under humid and dry atmospheres using samples of low‐activity waste (LAW) melter feed simulants. Melting of feed pellets in the presence of water vapor slightly decreased the temperature of primary foam onset for an extensively foaming feed, but did not significantly affect the feed volume expansion by foaming or the foam‐collapse temperature. Sets of feed expansion experiments and evolved gas analyses were also performed to check the effect of thermal history on conversion behavior of LAW feed samples. The thermal history was varied by testing feed samples prepared as direct slurry, loose powder, and slow‐ and fast‐dried pellets. The sample preparation methods and the sample shape were not found to influence foaming parameters, except for the direct slurry where the low‐temperature swelling prevented the foam onset and collapse temperatures to be determined.