METHODOLOGY OF SELECTING CEMENT MATRIX COMPOSITION FOR IMMOBILIZATION OF IRRADIATED URANIUM-GRAPHITE FUEL

The Impulse Graphite Reactor (IGR) is a unique nuclear facility in the world. The core of the research reactor is a stack of uranium-graphite blocks (fuel elements) enriched to 90 wt. % in 235 U isotope. As part of the project on conversion of the IGR reactor to low-enriched uranium fuel, the specialists of the Institute of Atomic Energy (IAE) studied the possibility of immobilizing the first core in a cement matrix. Research into the immobilization process included both the formation of technical requirements for the uranium-graphite fuel matrix, determined by the conversion conditions, international and national standards, and the selection of the composition and ratios of the matrix components. The paper presents the results of an analysis of modern achievements in the field of immobilization of radioactive waste and irradiated graphite, the formation of matrix acceptability criteria for the immobilization of highly enriched IGR fuel, and methods for determining whether the matrix properties correspond to the established criteria. The matrix compositions for immobilization of the irradiated fuel of the IGR reactor were selected experimentally, based on such characteristics of the cement slurry as bleed water, viscosity, setting time, uniformity of volume change, homogeneity and strength of the samples. To determine the above characteristics, the methods used to determine the characteristics of cement slurries were used and improved. They have proven their suitability. The requirements used to select the composition of matrices for immobilization of spent uranium-graphite fuel of the IGR reactor turned out to be applicable and sufficiently constructive, and can also be recommended for solving issues of selecting the consistency of matrices for immobilization of other types of RW.