The present invention relates to a high-level radioactive waste, for example a ceramic material for encapsulation of waste resulting from reprocessing of irradiated nuclear fuel. Future generation of waste streams due to power generation by the so-called Purex process (so-called improved Purex process) may not be suitable for containment by established vitrification techniques. The present invention provides a ceramic waste immobilization medium that contains waste derived from a reprocessed nuclear fuel combination and wherein waste ions from at least a fission product in the irradiated nuclear fuel are dissolved substantially in the form of a solid solution Wherein the ceramic waste immobilization medium has a matrix containing phases of hollandite, perovskite and zirconolite in a matrix in which the waste ions are dissolved, the wastes being derived from non-fuel components of the fuel combination It is made up of a considerable amount of material. The present invention also provides a method of immobilizing waste from a reprocessed nuclear fuel combination, the method comprising: contacting the liquid containing the waste with a precursor material comprising an oxide or oxide precursor of at least titanium, calcium and barium; Mixing to form a slurry; Drying the slurry; And calcining the dried slurry under a reducing atmosphere to form a powder, wherein the powder contains 30-65 wt% of waste.
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