Feed-to-glass conversion during low activity waste vitrification

The thermal history of the nuclear waste feed during melting has a strong effect on the rate of melting, thus strongly affecting the efficiency of the nuclear waste cleanup. Based on our previous work that addressed the high-level waste (HLW) cold-cap formation and structure, we studied the feed-to-glass conversion of low-activity waste (LAW) slurry, which has significantly different chemical composition and resultant physicochemical properties. To simulate the conditions during feed-to-glass conversion, samples were prepared by rapid water evaporation from the LAW slurry. The resulting cold-cap was more porous than a typical HLW cold-cap, and its heat conductivity was shown to be significantly lower. In addition, the presence of salts in the LAW, such as borax decahydrate, distinctly affected the slurry properties during boiling, possibly helping the LAW slurry spread across the melter and preventing build-ups of cold-cap leading to feeding interruptions.