(11c) Modeling of Cold-Cap Reactions for Vitrification of Nuclear Waste Glass Based On Simultaneous Differential Scanning Calorimetry–Thermogravimetry (DSC-TGA)

Chun, J., Pacific Northwest National Laboratory
Pokorny, R., Institute of Chemical technology in Prague
Hrma, P., Pohang University of Science and Technology

During the waste-glass vitrification, multiple and overlapping gas-evolving reactions called cold-cap reactions take place, leading to the feed-to-glass conversion. The cold-cap reactions involve mass losses and foaming which significantly influence the mass and heat transfers, and eventually affect the melting rate in the vitrification. We studied the cold-cap reactions of a representative waste glass feed using DSC-TGA and developed a kinetic model. The model is based on the assumption that the reactions are nearly independent and can be approximated by an nth order kinetic equation. To separate the reaction heat from both the heat associated with the heat capacity of the feed and experimental artifacts, we employed the run/rerun method, which enabled us to define the degree of conversion based on the reaction heat and to estimate the heat capacity of the reacting feed. We obtained the kinetic parameters using the Kissinger method combined with least squares analysis. The resulting mathematical simulation of the cold-cap reactions provides a key element for the development of an advanced cold-cap model.