The Hanford Site contains 177 underground tanks with radioactive waste that will be vitrified, i.e., immobilized by converting it to glass in electric melters. After pretreatment, the waste slurry will be mixed with glass-forming minerals, and the resulting feed will be charged into the melter. For each waste composition, the glass must be formulated to possess acceptable processing and product behavior defined in terms of physical properties that guarantee that the glass is easily made and resists environmental degradation. On heating, the feed undergoes complex reactions. The large variability of waste compositions presents numerous technological challenges: undesirable insoluble solids and molten salts may segregate; foam may hinder heat transfer and slows down the process; and on cooling, the glass may precipitate crystalline phases.