ZIRCONOLITE AS A MATRIX FOR IMMOBILIZATION OF HIGH-LEVEL RADIOACTIVE-WASTES

The term zirconolite embraces three polymorphic varieties of a mineral with composition (Ca, Na, REE, Th)(2)Zr-VIII(2)VII(Ti, Nb)(3)(VI)(Fe, Ti)O-V,IV(14) and orthorhombic (zirconolite-30), trigonal (zirconolite -3T), and monoclinic (zirconolite-2M) crystal lattices. The highest co ncentrations of isomorphic components in natural and synthetic zircono lites (as recalculated to oxides) are 20-25 wt % of actinides, 15-18 w t % of combined Nh and Ta, 12-15 wt % of REE, 11 wt % of Pu etc. The c ations with diverse charges (+1 to +5) and ionic radii (0.4 to 1.4 Ang strom) can be incorporated in the zirconolite structure. Such paramete rs are typical of most radionuclides that remain in the high-level rad ioactive wastes (HLW) after removal of Cs and Sr isotopes. High resist ance of zirconolite to radioactive and hydrothermal attacks, wide soli d solution limits, and well-developed production technology make this mineral the best waste form. for immobilisation of actinides of high-l evel radioactive wastes, as well as weapon plutonium.