Abstract
Self-propagating high-temperature synthesis (SHS) of mineral-like matrices based on pyrochlore (Y2Ti2O7) and zirconolite (CaZrTi2O7) phases for immobilization of actinide-containing wastes (HLW) was studied. Thermodynamic analysis of the systems Ti-ZrO2-CaO-Y2O3-MenOm (Me = Mo, Fe, Ni, Cr, Mn, Cu) was performed. The possibility of preparing matrices based on the structure of titanium pyrochlore Y2Ti2O7 enriched in zirconium was demonstrated. The dependences of the formation and ratio of crystalline phases in SHS products on the charge composition and HLW concentration were revealed. The HLW components do not form intrinsic crystalline phases and are incorporated as isomorphous impurities in the crystal lattices of pyrochlore, zirconolite, and perovskite. The advantages of using Fe2O3 as oxidant were demonstrated. It prevents possible loss of HLW elements, associated with high-temperature evaporation of the oxidant. A matrix material consisting of two phases: (1) titanate pyrochlore Y2Ti2O7 containing HLW elements and enriched in zirconium and (2) Fe metal was prepared. The total content of lanthanides in separate pyrochlore crystals varies from 0.9 to 1.6 at. %, with 27 to 31% replacement of Ti atoms by Zr atoms. The study was performed with simulated HLW.
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