Thermal evolution in molten salt conditioned waste drums

This paper presents an experimental and numerical investigation of the thermal evolution of a conditioned molten salt oxidation (MSO) residue contained within 100 L drums. Three types of binders were employed: (i) alkali-activated material (AAM) with a metakaolin precursor (AAM_MK), (ii) AAM with a blast furnace slag (BFS) precursor, and (iii) a blended cement mix, each with varying waste loadings. The study primarily involved isothermal and semi-adiabatic calorimetry experiments to develop a comprehensive dataset of hydration curves, which serve as direct inputs for a heat transfer model. Drum-scale experiments on the reconditioned MSO residue waste with metakaolin precursor were successfully designed and executed. Thermal evolution within the drum was monitored using thermal sensors strategically placed at various locations. A standard heat transfer model was employed for blind predictions of thermal evolution within the drum. Calorimetric measurements of the different waste forms indicated that the addition of MSO residue delayed hydration and geopolymerization in both the cementitious and alkali-activated matrices. The numerical model reasonably captured the primary features of thermal evolution, particularly the peak measured temperature data (> 80 ◦C) at the core of the drum conditioned with the AAM_MK binder, while also highlighting the uncertainty in the sensitive model parameters. It is anticipated that for typical drum sizes exceeding 200 L used in pre-disposal storage, peak temperatures could surpass 100 ◦C. Consequently, further studies on the long-term stability of reconditioned waste forms exposed to high early age temperatures are warranted.