The Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences (IGEM RAS)

N. P. Laverov, Academican, Vice President of RAS

T. S. Livshits, Senior Researcher

S. V. Yudintsev, Leading Researcher, Corresponding Member of RAS, e-mail: syud@igem.ru

B. I. Omelyanenko, Leading Researcher

B. S. Nikonov, Senior Researcher

The following specialists participated in these researchings: S. V. Stefanovskiy, N. S. Mikhaylenko, A. V. Mokhov, A. A. Lizin, A. N. Lukinykh, O. I. Stefanovskaya, S. V. Tomilin, Dzh. Dzhang, R. Yuing.

New synthetic minerals — complex cubic oxides with the pyrochlore- or garnet-type structure have been suggested as matrices for immobilization of long-lived actinides and REEactinide fraction derived from the high level liquid waste (HLW) after spent nuclear fuel reprocessing. The choice of these compounds is based on the existence of two (in the pyrochlore structure) or three (in the garnet lattice) different structural sites for cations with coordination number equal to 6 and 8 (pyrochlore) or 4, 6 and 8 (garnet). The selection of optimal confinement matrices composition considered strong correlations between cation’s dimensions in the different structural positions. From the maximal HLW components loading point of view the phases which octahedral sites are filled by cations of the IV group of the Periodical system with radii from 0,61 (Ti⁴⁺) to 0,72 (Zr⁴⁺) Angstroms are the most preferable among the pyrochlore-structure materials. The ferrite garnets in which all the tetrahedral and, at least, part of the octahedral sites are occupied by Fe³⁺ are also promising phases for this goal. These matrices accommodate the highest amounts of the elements of actinide or REE-actinide fractions varied from 30 wt.% in garnets up to 60 wt.% in pyrochlores. Another important parameter at selection of the materials for actinide waste immobilization is their response to radiation connected with radioactive decay. It was shown from experiments on heavy ion bombardment and doping of the promising materials with short-lived isotope Cm-244 that stability (dose of amorphization) of the ferrite garnet structure at irradiation is close to data for the titanate pyrochlore, but it is significantly (2–3 times) lower than values for aluminate garnets and especially stannate or zirconate pyrochlores. Amorphization (lattice disordering) of the matrices due to actinide decay may influence solubility in the underground water and confinement properties in respect of the radioactive waste as well. Analysis of the problem is a main object of our further research.

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