Alternative Reductants for Foam Control During Vitrification of High-Iron High Level Waste (Hlw) Feeds

Foaming during vitrification of radioactive waste in Joule-Heated Ceramic Melters (JHCM) is exacerbated by trapping of evolving gases, such as CO 2 , NO x and O 2 , beneath a viscous reaction layer. Foaming restricts heat transfer during melting. Sucrose is employed as the baseline additive at the Hanford site in Washington State, USA to reduce foaming. Alternative carbon-based reductant additives were explored in simulated, inactive Hanford high-iron HLW-NG-Fe2 feeds, for both their effect on foaming and to give insight to the behaviour of multivalent species in glass melts under different redox conditions. Graphite, coke (93% C), formic acid and HEDTA additives were compared with sucrose, and a feed with no additive. Graphite and coke additions proved most effective in reducing the maximum foam volume by 51 ± 3% and 54 ± 2%, respectively, compared with 24 ± 5% for sucrose. Lower foaming could result in more efficient vitrification in JHCMs. Reductants also affected redox ratios in the multivalent species present in the feed. The order of reduction, Mn 3 + /Mn 2 + > Cr 6 + /Cr 3 + > Ce 3 + /Ce 4 + > Fe 3 + /Fe 2 + was as predicted on the basis of their redox potentials. There is less reduction overall, particularly in the Fe 3 + → Fe 2 + , than predicted by the calculations, attributed to the oxygenated atmosphere of the experiments.