PNNL

Abstract

This study examines the use of boron nitride (BN) and coke dust as alternative reductants for low-activity waste vitrification in scaled melter systems, intended to enhance operational flexibility at the Hanford Waste Treatment and Immobilization Plant. The baseline reductant, sucrose, while effective in controlling foam and glass redox, produces challenging off gas emissions during processing. Early crucible-scale testing indicated that BN and coke effectively control foaming and glass redox, while significantly reducing acetonitrile emissions. Both real tank waste and simulant waste melter feeds were tested with BN and coke in this study. Rheological properties for melter feeds with both reductants were within operational limits, although the particle size of coke should be controlled and sufficient agitation is necessary to ensure smooth operations. While promising for handling and reduction of emissions, both simulant melter feeds demonstrated lower average glass production rates in the melter system compared with sucrose. In the radioactive system, the rates were more comparable to previously measured low activity waste feeds on the order of 1100 kg m2 day -1 for BN and 1700 kg m-2 day for coke. Further scale-up testing is required to interpret the processing rates in the context of the full scale melter systems and evaluate the cost-benefit impact of these reductants on efficiency and sustainability.