Combined truex-srex extraction/recovery process.

The United States Department of Energy Hanford site defense complex has the largest volume of stored nuclear waste in the US. The complex has been in existence for nearly fifty years, and the varied chemical operations over this time period have generated a wide variety of wastes. The aqueous wastes, both high-level and TRU (transuranic), are stored in underground single-shell and double-shell tanks. Because the aqueous wastes are made alkaline (pH ∼14) to prevent corrosion of the carbon steel liners of the tanks, the uranium, TRUs and 90Sr, together with most of the fission products, are largely concentrated in the insoluble sludge formed by the hydroxides, phosphates, and silicates of metal ions such as aluminum, iron, zirconium, and bismuth. Fission products cesium and technetium are largely concentrated in the supernatant solution.