Abstract: The composition of radionuclide in high-level radioactive waste is complex resulting in an issue of strong selectivity in ceramics solidification. In this study, a novel method was proposed to simultaneously immobilize fission products and actinides in a simple process. Based on the ceramizable geopolymer design theory, a high-level radioactive liquid waste multiphase ceramics-based form was prepared by mixing simulated high-level radioactive liquid waste with metakaolin, slag, silica fume and nano-zirconia as main raw material and 1.5-modulus potassium water glass as activator. After mixing of high-level radioactive liquid waste, raw materials and activator, and curing at room temperature for 7 d, the hardened cement waste form was transformed into a geopolymer-based multiphase ceramics high-level radioactive liquid waste form by heat treatment at 1 100 ℃. The leaching resistance properties of waste form were tested by static leaching method. XRD, SEM-EDS, XPS and other analytical techniques were employed to explore the mechanism of geopolymer ceramization conversion process, nuclide immobilization mechanism and Ce element oxidation status. The results show that the immobilization mechanisms of simulated nuclides are both chemical and physical forms. Large amounts of the simulated nuclide transfer into the crystal structure of leucite (cubic), zirconia (cubic), zircon lattice or form ceramic phases. Small amounts of nuclide are wrapped in glass phases. Cs and Sr are uniformly distributed, and Ce and Nd are enriched in the glass phase. Leaching results show that the geopolymer-based multiphase ceramics high-level radioactive liquid waste form has excellent leaching resistance property for immobilizing simulated nuclide of various valences and radii. The 28 d normalized element leaching rates of Cs and Sr are 10-2g/(m2·d), and those of Nd and Ce are 10-4~10-5 g/(m2·d). This paper provides a design and preparation method of high-level radioactive waste form that can simultaneously solidify multiple nuclide by combining cement, glass and ceramics solidification methods with simple process, which casts a new light on the effective solidification of high-level radioactive waste.
Key words: geopolymer, leaching rate, multiphase ceramics, high-level radioactive liquid waste, simultaneous solidification, immobilization mechanism
Declaration: This article is provided by CERADIR™ users or obtained from Internet, the content does not represent the position of CERADIR™. We are not responsible for the authenticity/accuracy of the article, especially the effects of the products concerned. This article is for study only, it does not constitute any investment or application advice. For reprinting, please contact the original author. If it involves the copyright and/or other issues, please contact us and we will deal with it asap! CERADIR™ has the interpretation of this declaration.
