Immobilization of technetium and rare earth-actinide fraction in crystalline matrices using self-sustaining high-temperature synthesis
The development of nuclear power engineering aggravates the problem of managing radioactive waste, including high-level waste (HLW). These HLW are immobilized in glasses now. However, this material manifests a rather low durability, which becomes still worse after glass crystallization. Therefore, glass cannot provide safe isolation of long-lived actinides and fission products in the underground repositories of HLW. Searching matrices for actinide immobilization was considered in a great number of papers that were mainly devoted to plutonium-containing waste of nuclear weapon production. Lately, essential attention is being paid to the investigation of matrices for waste fractions obtained from the separation of liquid HLW upon spent fuel reprocessing. One of the fractions contains a high amount of actinides and lanthanides, sometimes Zr and other admixtures. Less attention is paid to the isolation of long-lived fission products, 99Tc being one of the most hazardous among them. This is related to its long half-life time, a high content in fission products, high water solubility of Tc7+ compounds and the ability to migrate in the form of TcO4-. The paper analyzes the possibility of incorporating the rare earth and actinide fraction as well as Tc in matrices of pyrochlore, perovskite, rutile, and metallic alloy using the self-sustaining high-temperature synthesis.