Sintered zirconolite ceramics for immobilization of actinide-containing radioactive waste

Ceramic samples based on uranium containing zirconolite 5, 10 and 20 wt% of UO2 we prepared by cold pressing and sintering at 1300 deg. C. Initial oxide mixtures were mechanically activated. Examination of these samples by X-ray diffraction, optical and electron microscopy has shown that the main phase in all samples is zirconolite (up to ∼80% of total bulk) existing in two varieties with different uranium content. Minor phases of zirconolite and rutile were also present. In the samples produced by cold pressing and sintering as in hot-pressed and inductively-melted samples studied elsewhere, uranium enter zirconolite in zirconium sites in the tetravalent state. (author)