Morphological change in cold cap by dibutyl phosphate: The influence of zirconium and molybdenum in high-level liquid waste

Abstract Dibutyl phosphate (DBP) is a problematic compound in reprocessing plants, affecting not only the extraction processes of U and Pu, but also the vitrification of high-level liquid waste (HLLW). Previous full-scale glass melter tests indicated that even a minor amount of DBP in simulated HLLW altered the cold-cap morphology, making it larger and thicker. In this study, small-scale melter tests revealed that the influence of DBP on cold-cap morphology is related to the Zr/Mo concentration ratio in HLLW. When the Zr/Mo ratio was high, a tall wall composed of calcined waste components formed around the cold cap, and a thick waste layer developed at its bottom. These DBP-induced changes were mitigated by lowering the Zr/Mo ratio; the cold cap then adopted a flatter morphology similar to that observed in the absence of DBP. Graphical abstract