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Phase and Chemical Stability of Murataite Containing Uranium, Plutonium and Rare Earths

Published online by Cambridge University Press:  21 March 2011

S.V. Yudintsev ,
S.V. Stefanovsky ,
B.S. Nikonov  and
B.I. Omelianenko
S.V. Yudintsev
Affiliation:
Institute of Geology of Ore Deposits, Staromonetny 35, Moscow 109017, Russia
S.V. Stefanovsky
Affiliation:
SIA "Radon", 7-th Rostovskii per., 2/14, Moscow 119121, Russia
B.S. Nikonov
Affiliation:
Institute of Geology of Ore Deposits, Staromonetny 35, Moscow 109017, Russia
B.I. Omelianenko
Affiliation:
Institute of Geology of Ore Deposits, Staromonetny 35, Moscow 109017, Russia
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Abstract

Murataite –a complex actinide (An)- and rare earth element (REE)-bearing oxide with a cubic fluorite-related lattice – is one of the promising host-phases for immobilization of Pu-containing waste. The murataite phase composition corresponds to the empirical formula:A4B2C7O22-x, where the A-sites are occupied by Ca, Mn, REE, and An (U); B sites – by Mn, Ti,Zr, and An (U); and C sites – by Ti, Al, and Fe. The total amount of the actinides (U) and REE (Ce, Gd) in the murataite may exceed 20 wt%. In contrast to the other prospective hosts for actinide waste immobilization (cubic zirconia and pyrochlore), murataite accommodates higher amounts of corrosion products(Al, Fe) along with the actinides. The authors compared murataite-based ceramics having similar compositions and produced by melting in a high-temperature resistance furnace or via inductive melting in a cold crucible. Eight samples of the murataite-based ceramics were produced and investigated in detail. Murataite was found to be the major phase in four of the samples – with a basic composition, in wt%, of: 5.0 Al2O3, 10.0 CaO, 55.0 TiO2, 10.0 MnO, 5.0 Fe2O3, 5.0 ZrO2, and 10.0 UO2. These samples were produced by melting in a resistive furnace and in the cold crucible and included Gd-bearing samples and one Pu-bearing sample. The extra phases were other titanates: (from more to less typical) rutile, pyrochlore, zirconolite, crichtonite, pseudobrookite, and perovskite (in the Pu-doped samples only). Three varieties of the murataite, with 3-, 5-, and 8-fold fluorite-type lattices, were observed. Addition of uranium and rare earth oxides stabilizes pyrochlore as the major phase, whereas addition of zirconia yields zirconolite. Plutonium stabilizes the perovskite-type phase, probably due to the formation of Pu3+. The maximum waste oxide content in the murataite for the elements studied was found to be 10% ZrO2, 12% CeO2, 13% Gd2O3, and 14% UO2. Waste element partitioning among the murataite and all the other phases with similar fluorite-related structure (pyrochlore and zirconolite) was analyzed. The uranium leach rate for the sample with maximum murataite content was measured using a procedure similar to MCC-3. This leach rate was close to10-5 g/(m2*day) in a½-day test and decreased by more than one order of magnitude in 28-day tests. Investigation of the stability of the murataite structure after irradiation byheavy ions is in progress.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 663: Symposium – Scientific Basis for Nuclear Waste management XXIV , 2000 , 357
Copyright
Copyright © Materials Research Society 2001

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References

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