Leaching of americium-241, plutonium-238 and matrix elements from perovskite-based ceramics
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Leaching of americium-241, plutonium-238 and matrix elements from perovskite-based ceramics A.V. Ochkin,1 S.V. Chizhevskaya,1 N.E. Archakova (Cherniavskaya),1 A.O. Merkushkin,1 I.A. Petukhova,1 N.P. Mikhailenko,2 S.V. Stefanovsky2 1 2
D. Mendeleev University of Chemical Technology, Miusskaya sq. 9, Moscow 125047 RUSSIA SIA Radon, 7th Rostovskii per. 2/14, Moscow 119121 RUSSIA, [email protected]
ABSTRACT Perovskite-based ceramics ABO3 (A = La or Gd; B = Al or Fe) and a pseudobinary system: LaAlO3 + CaZrTi2O7 are promising matrices for immobilization of actinide fraction of HLW. The ceramic samples containing 241Am, 238Pu or 147Pm were prepared by cold pressing in pellets at 100-300 MPa and sintering at 1300-1500 0C. Leach rates of radionuclides and matrix elements (La, Gd, Al and Fe) from powders were measured using Soxhlet unit. Sintered ceramics in the series: LaAl1-xFexO3 were composed of perovskite phase. Ceramics in the compositional series xLaAlO3 + CaZrTi2O7 (0.4 ≤ x ≤ 6) consisted of perovskite, zirconolite, and baddeleyite at x = 0.4 and x = 0.7, and perovskite and baddeleyite at higher x values. Leach rate of radionuclides and matrix elements from all the ceramics were lower than 10-8 g·cm-2·day. INTRODUCTION Perovskite is one of the Synroc phases and serves as a host for strontium and rare earths, mainly lanthanides as well as minor actinides [1]. In the frame of high level waste (HLW) partitioning concept rare earths and actinides are separated from Cs/Sr fraction to be conditioned into a ceramic waste form. One of the possible process schemes provides for a separation of Am, Cm, minor U, Np and Pu, and rare earths but another partitioning scheme yields the fraction containing Zr [2]. The Zr free fraction may be immobilized in perovskite ceramics but incorporation of the Zr-bearing fraction in ceramics requires an additional zirconolite or pyrochlore phase. In our previous works [3-5], we described results on development and examination of the perovskite-based ceramics. Special attention was paid to development of synthesis method using a mechanical treatment/activation because production of the perovskite ceramics requires higher temperatures as compared to zirconolite ceramics due to higher melting point of perovskite (1960 0C [6]) than zirconolite (1525 0C [7]. It has been demonstrated that the perovskite-based ceramics are high leach resistant [3-5] and the samples prepared using the mechanical activation of source oxide mixtures have after sintering strong mechanical integrity [4]. In the present work we describe new results on phase composition and leach testing of ceramics in the systems: La2O3 – Al2O3, La2O3 – Fe2O3, and La2O3 – Al2O3 - Fe2O3 doped with 241 Am, 238Pu, and 147Pm and pseudobinary system LaAlO3 – CaZrTi2O7. EXPERIMENTAL Ceramic samples with various La2O3 to Al2O3 and La2O3 to Fe2O3 ratios were produced from intermixed oxide powders mechanically treated/activated in an apparatus with a rotating
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magnetic field - Linear Inductive Rotator LIV-0.5E (Russian design)
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