Synroc/glass composites were designed for simulated Hanford HLW sludges containing U (the current “All-Blend” formulation). The composite contained ∼ 50 wt% of simulated HLW (oxide equivalent), to which ∼ 6, 10, 10, and 24 wt% of CaO, Al2O3, TiO2 and SiO2 were added, and melted under an argon atmosphere at 1350°C. The phase assemblage consisted of zirconolite, perovskite, spinel, nepheline, whitlockite and glass as major phases. Seven-day PCT tests yielded values of < 0. 1 g/m2 for all elements studied. The PCT results were tolerant to changes of ∼ 20% of the inventories of the additives, and to variations in redox conditions.
Technetium separated out during decontamination of liquid Hanford wastes can be incorporated as metal in hot-pressed Synroc prepared under reducing conditions, and its leach resistance is good (∼ 10∼3 g/m2/day at 70°C), and can be improved by alloying with iron group metals. With a choice of “neutral” (P(O2) ∼ 10−4 atm., near the Ni/NiO buffer) hot-pressing conditions, Tc can also be incorporated as Tc4+, substituting for Ti4+ in the ceramic phases, and in this form, it should be highly leach resistant also.