Silicate Matrix of Actinide-Bearing Wastes

The development of nuclear energetics and fulfillment of military programs in Russia resulted in the accumulation of enormous radioactive wastes including the high level radioactive wastes (HLW). According to the existing concept, HLW should be enclosed into secure matrices for the subsequent burial in underground repositories. As a rule, HLW consist of various chemical elements with different half-life periods, and this hampers the choice of appropriate conserving matrices. The problem is simplified after the separation of elements into similar in properties groups of shortand long-living nuclides. By the present time, the methods of HLW separation into the Cs‐Sr and actinide fractions have been elaborated [1]. Elements, such as Zr and REE, may be extracted along with actinides. The extraction of actinides and REE was named as a TRUEX technology [2] by analogy with the PUREX technology (an extraction of Pu and U during the regeneration of irradiated fuel). Most rigorous requirements are placed upon the materials used for the conservation of actinides characterized by long half-life and high toxicity. One of feasible solutions consists in the application of crystalline phases with a high isomorphic capacity for these elements and a radiation and chemical stability [3‐6]. Another way to increase the safety of HLW burial is related to the creation of such waste forms, which would be in equilibrium with repository rocks. This approach was formulated as a principle of phase and chemical compliance of matrices and host medium [6]. Rocks proposed for HLW repositories consist of 95‐ 99% silicates. Therefore, it may be expected that the incorporation of wastes into Si-bearing phases will slow down the failure of matrices and removal of radionuclides from the repository. Results of the investigation on phases with garnet and apatite-britholite structures are reported in this communication. The choice of phases is based on their high capacity for waste components, as was established by the study of natural counterparts and supported by experiments [7‐10]. Samples were synthesized with an induction melt