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Phase Compositions and Elements Partitioning in Two-Phase Hosts for Immobilization of a Rare Earth-Actinide High-Level Waste Fraction

Published online by Cambridge University Press:  10 February 2011

S.V. Stefanovsky ,
S.V. Yudintsev ,
B.S. Nikonov ,
A.V. Ochkin ,
S.V. Chizhevskaya  and
N.E. Cherniavskaya
S.V. Stefanovsky
Affiliation:
SIA Radon, 7th Rostovskii per., 2/14, Moscow119121 RUSSIA, itbstef@cityline.ru
S.V. Yudintsev
Affiliation:
Institute of Geology of Ore Deposits, Russian Academy of Sciences, Staromonetni 35, Moscow RUSSIA
B.S. Nikonov
Affiliation:
Institute of Geology of Ore Deposits, Russian Academy of Sciences, Staromonetni 35, Moscow RUSSIA
A.V. Ochkin
Affiliation:
D. Mendeleev University of Chemical Technology, Miusskaya, 9, Moscow RUSSIA
S.V. Chizhevskaya
Affiliation:
D. Mendeleev University of Chemical Technology, Miusskaya, 9, Moscow RUSSIA
N.E. Cherniavskaya
Affiliation:
SIA Radon, 7th Rostovskii per., 2/14, Moscow119121 RUSSIA, itbstef@cityline.ru
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Abstract

In two-phase matrices based on pyrochlore-oxide, perovskite-oxide, and pyrochlore-zirconolite assemblages as much as 40 wt.% of the product can consist of an incorporated rare earth - actinide fraction of high level wastes (HLW). In zirconolite, with a nominal stoichiometry of AVIIIBVICV-VI2O7 the actmide and rare earth ions occupy VIII- and VII-fold coordinated sites. Charge compensation is achieved by replacement of Ti4+ with lower valence ions such as Al3+, Fe2+/3+. Mg2+, etc, that have similar radii. The highest lanthanide incorporation (45 wt.% σREE2O3) was exhibited by a calcium free zirconolite containing 8 wt.% A12O3 or 0.7 formula units (f.u.). In pyrochlore (AVIII2BVI2O7−x) actinides and rare earths occupy A-sites. Their incorporation does not require simultaneous ionic substitution in the B-sites, for example Al3+ or Fe 2+/3+ for TI4+, to achieve charge compensation; this simplifies the required composition of the system. Pyrochlore ceramics are suitable for immobilization of wastes with relative elevated actinide content. For a high zirconia, waste ZrO2-based or two-phase pyrochlore-dioxide, perovskite-dioxide or pyrochlore-zirconolite ceramics are preferable. All these wasteforms may be produced via melting

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 608: Symposium QQ – Scientific Basis for Nuclear Waste Management XXIII , 1999 , 407
Copyright
Copyright © Materials Research Society 2000

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References

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