Selection of Matrices for Immobilization of Actinide Fraction of HLW
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II3.29.1
SELECTION OF MATRICES FOR IMMOBILIZATION OF ACTINIDE FRACTION OF HLW A.V. Ochkin1, S.V. Stefanovsky2, S.I. Rovny3 1
D. Mendeleev University of Chemical Technology, Moscow, Russia; SIA Radon, Moscow, Russia; 3 PA Mayak, Ozersk, Chelyabinsk reg., Russia. 2
ABSTRACT HLW after the separation of U, Pu and Np contains two major radionuclide groups: fission products and TRU elements. The later ones are the most dangerous and should be separated in the special actinide fraction. This process has been realized at PA “Mayak”. The composition of the actinide fraction depends on a separation method: A. Radionuclides of Am and Cm with minor amounts of U, Np and Pu. B. Radionuclides of Am and Cm with minor amounts of U, Np and Pu and also REEs. C. Radionuclides of Am and Cm with minor amounts of U, Np and Pu and also REEs and perhaps some amount of Zr. The fraction with composition A can be burned off in fast reactors whereas the fractions with compositions B and C should be immobilized in stable matrices. Alpha-Activity of actinide fraction is subsequently determined by 244Cm, 241Am, 244Am, 239Pu and 242Pu during a long-term storage. The storage time depends on conditions and can reach several hundreds of thousands years. The main requirements to matrices are chemical and radiation resistances. The fraction with composition B can be incorporated in perovskite ceramics whereas in case of composition C the additional zirconolite and/or pyrochlore phases are necessary. INTRODUCTION High level waste (HLW) is well-known to be a complex mixture of more than 90 radionuclides of fission products, corrosion products, transuranic (TRU) elements, and process contaminants [1]. Currently HLW from spent fuel reprocessing is stored in stainless-steel tanks and only its small part is vitrified with production of borosilicate [2] or aluminophosphate glass [3]. However stability of glass can not be guaranteed for long periods necessary to decay actinide elements presenting in HLW. There are a lot of proposals what should be done with HLW. Among them the most promising are their incorporation in ceramics [4]. Special ceramic waste form named Synroc was designed in ANSTO, Australia [4]. However, Synroc is not appropriate matrix for immobilization of cesium (one of the most important fission products) and other alkali elements (process contaminants). This demonstrates that solidification of HLW as it is can not be considered as suitable route. Due to this circumstance a HLW partitioning concept has been proposed [5]. According to this concept HLW must be partitioned into short-lived Cs/Sr and long-lived (rare earth – actinide) fraction to be conditioned separately. In this paper we discuss a general approach to select matrices for immobilization of partitioned HLW taking into account HLW partitioning scheme implemented at PA “Mayak” [5].
II3.29.2
APPROACH AND DISCUSSION The problem of high level waste (HLW) management is determined by long-lived radionuclides with half-life periods more than 15 years. HLW after spent fuel reprocessing
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