A new alkali-alumino tellurite glass composition was developed to immobilize highly-volatile technetium (Tc) wastes generated from the pyrochemical processing technology. Tellurite glass can incorporate up to 7 mass% of rhenium (Re, used as a surrogate for Tc) with an average retention of 86%. Normalized elemental releases evaluated by seven-day product consistency test (PCT) satisfied the immobilized low activity waste requirements of United States when concentration of Ca(ReO₄)₂ in the glass was < 12 mass%. Re ions form Re⁷⁺ and are coordinated with four oxygens to form ReO₄^- tetrahedra. These tetrahedra bond to modifiers such as Ca²⁺ or Na⁺ that are further connected to the tellurite glass network by Ca²⁺ (or Na⁺) – non-bridging oxygen bonds