Approximately 130M L of sludge/supernate high-level radioactive waste is currently stored in underground carbon steel tanks at the Savannah River Site in Aiken, South Carolina. The Defense Waste Processing Facility (DWPF) began immobilizing these wastes in borosilicate glass in 1996. Currently, the radioactive glass is being produced as a sludge-only composition by combining washed high-level sludge with glass frit and melting. The glass is poured into stainless steel canisters that will eventually be disposed of in a permanent geological repository. The focus of this report is on frit development activities conducted solely on the basis of predictions generated by DWPF's PCCS glass property-composition models.