Synthesis and Study of 239 Pu-Doped Gadolinium-Aluminum Garnet
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ABSTRACT Garnet solid solutions, Y3A15O 12-Gd 3A15O 12-Gd 3Ga5 O12 (YAG-GAG-GGG), are being considered as prospective durable host phases for the immobilization of actinide-containing waste with complex chemical compositions. Garnet samples with the suggested simplified formula: (Gd,Ce .... )3(AI,Ga,Pu,. )5012 containing from 3.4 to 5.3 wt.% 2 39 Pu and 3.6-5.5 wt.% Ce have been synthesized through melting of oxide starting materials in air using a hydrogen torch. Calcium and Sn were added to increase the Pu incorporation into the garnet lattice through ion charge and size compensation for Pu 4 +. Polycrystalline materials obtained in the experiments consist of garnet, perovskite and other phases and were studied by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). Our results confirmed that the use of compensating elements such as Ca and Sn allow for significant incorporation of Pu and Ce (not less than a few wt.%) into the garnet structure. The preliminary conclusions thus so far indicate that garnet solid solution compositions may incorporate simultaneously trivalent and tetravalent actinides in significant quantities because they occupy different positions in the garnet structure.
INTRODUCTION Plutonium waste residues originate from nuclear weapons production and may contain more than 50 % of chemical impurities including such elements as Am, Al, Mg, Ga, Fe, La, Na, Mo, Nd, Si, Ta, Ce, Ba, W, Zn, C and Cl. While for some of these residues, direct conversion to traditional glass or ceramic waste forms may be difficult, ceramic waste forms based on durable actinide host-phases are preferred for Pu, Am and other actinide immobilization. Previous work has demonstrated that gamet/perovskite ceramics (Y,Gd,. ..)3(AI,Ga,...) 5 0 12/(Y,Gd,...)(AI,Ga,...)O3 are prospective durable materials which may allow the incorporation of Pu, Am and most elements listed above in the form of solid solution [1-4]. Under the same synthesis conditions without the addition of compensating elements (i.e., ion size and charge), GGG incorporates up to 6 wt.% Ce, but less than 0. 1 wt.% U. Pure YAG incorporates not greater than 0.5 wt.% Ce [2]. Also, it has been demonstrated that the use of Sn and Ca as compensating (of ion size and charge) admixtures significantly increases the incorporation of U into garnet lattice [3]. However, Ce as well as U can not be considered as acceptable surrogates for Pu. Therefore, experimental studies of garnet and perovskite host-phases for Pu incorporation using Pu and not surrogate elements are required. The main goal of this work was to confirm the possibility of obtaining garnet solid solution with significant amounts of Pu through melting in air of oxide starting materials.
419 Mat. Res. Soc. Symp. Proc. Vol. 608 © 2000 Materials Research Society
EXPERIMENTAL To reduce the cost of experiments with Pu, we opted to make small samples of 0.5-1.0 gram of starting materials and using melting the oxide reagents in air as the synthesis method. In order to carry out melting of the cold p
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