Effect of Synthesis Conditions and Actinide Contents on Phase Composition of Actinide Bearing Ceramics
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(IIHFWRI6\QWKHVLV&RQGLWLRQVDQG$FWLQLGH&RQWHQWVRQ3KDVH&RPSRVLWLRQRI $FWLQLGH%HDULQJ&HUDPLFV A.G. Ptashkin1, S.V. Stefanovsky1, S.V. Yudintsev2, S.A. Perevalov3 1 SIA Radon, 7th Rostovskii per., 2/14, Moscow 119121 RUSSIA 2 Institute of Geology of Ore Deposits, Staromonetnii per. 35, Moscow 109017 RUSSIA 3 Vernadsky Institute of Geochemistry and Analytical Chemistry, Kosygin st., 19, Moscow, RUSSIA $%675$&7 Pu-bearing zirconolite and pyrochlore based ceramics were prepared by melting under oxidizing and reducing conditions at 1550 0C. 239Pu content in the samples ranged between ~10 and ~50 wt.%. Phase composition of the ceramics and Pu partitioning were studied using X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive system (SEM/EDS). Major phases in the samples were found to be the target zirconolite and pyrochlore as well as a cubic fluorite structure oxide. Normally the Pu content in the Pu host phases was 10-12 wt.%. This corresponds to the Pu content recommended for matrices for immobilization of excess weapons plutonium. At higher Pu content (up to 50 wt.%) additional phases, such as a PuO2based cubic fluorite-structured solid solution, perovskite, and rutile were found. ,1752'8&7,21 Actinides are the most hazardous constituents of high level wastes (HLW) due to long halflifes and high radiotoxicity. Currently, significant volumes of Pu- and Am-containing sludges that need to be conditioned are being stored at Minatom of Russia and US DOE sites [1]. A great deal of work was performed on development and testing of immobilization forms for excess weapons plutonium during the last decade [1-3]. Both vitreous and ceramic forms were considered. The ceramic forms are more thermodynamically stable, leach and radiation resistant and they are believed to be preferable matrices for actinides, including plutonium [2,3]. The ceramics studied in the most detail are based on phases with fluorite-derived structure – pyrochlore and zirconolite. They have been proven to be the highest leach and radiation resistant among all the candidate phases [4] and matrices based on these phases have been selected as Pu immobilization forms [2,3]. Significant attention was paid to the selection of actinide waste form production technology. LLNL scientists have selected a cold pressing and sintering technology [5]. Alternative hot uniaxial or isostatic pressing have been proposed at ANSTO [6]. In Russia, several technologies are under consideration now prior to a final decision [1]. One of them is based on inductive melting in a cold crucible (IMCC) [7,8]. Extensive studies were performed on the IMCC of ceramics and glass ceramics containing uranium and various actinide simulants (lanthanides) [712], but melting tests with actual Pu were performed only for glasses [13]. A lab-scale unit based on the IMCC has been constructed by specialists of SIA Radon and the Vernadsky Institute of Geochemistry and Analytical Chemistry this year. This unit will be used for experiments with minor actual actinides.
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