Change of structure and properties of vitrified radioactive wastes during long-time storage in an experimental repository

Abstract

Scanning electron microscopy, x-ray phase analysis, and infrared spectroscopy are used to study samples selected from a near-surface zone of glass blocks of vitrified radioactive wastes from nuclear power plants after they have been in storage in an experimental repository for 17 years. It is shown that only a thin surface layer of the glass blocks undergoes any changes due to environmental factors, and quartz-like and alumosilicate embryos are found on this layer.The world regards the vitrification of high-and medium-level wastes as one of the most promising methods of isolating such wastes from the biosphere, but this method has only limited application at the present time [1,2]. This is due to the problems associated with the operation of high-temperature melters (corrosion resistance of structural materials and electrodes, volatilization of the components of the wastes), and the uncertainty in the behavior of vitrified wastes during long-term storage in different geological media for periods up to several thousands of years. The main methods for evaluating the stability of the vitrified wastes are:• leaching samples under conditions simulating the medium in the repository or under more stringent conditionsin corrosive media at high temperature and pressure, which make it possible to predict the change of the structure and the properties over long periods of time; • tests in underground laboratories or at sites approximating real conditions of long-time storage; • study of the natural analogs and archeological data. Accelerated methods of determining the corrosion resistance of solidified forms of radioactive wastes, including vitrified wastes, make it possible to achieve changes of their structure and properties over relatively short times and make comparative estimates as a function of the composition and synthesis parameters. As a rule, the conditions under which testing (temperature and radiation fields, leaching medium) is performed, differ substantially from the real conditions in a repository and, correspondingly, the data obtained on the corrosion resistance of solidified wastes can be too high or too low. The known natural analogs (obsidian, tektites, basaltic glasses) and archeological artifacts have very different chemical compositions from real vitrified wastes, so that the data on the changes occurring in these materials can be transferred to vitrified wastes only with great care.The best method for evaluating and predicting the behavior of vitrified wastes under the conditions of long-time storage is experimental storage under test area conditions (underground laboratories and near-surface or deep repositories) with Britain. periodic sampling of the material being tested. In the case of vitrified high-level wastes, the interaction of the products of radiolysis of water with the surface of the glass has a large effect on the glass matrix, while this effect is negligible for vitrified medium-level wastes.The glasses were placed in an experimental repository in Canada, Sweden, France, USA, Belgium, ...

Phosphate-Mediated Remediation of Metals and Radionuclides

“…Chemical and physical methods, including excavation and soil capping [21,22], pump and treat technologies [23,24], mineral adsorption [25][26][27], mineral precipitation [28,29], complexation [30][31][32], adsorption to permeable zero-valent iron and hydroxyapatite reactive barriers [33][34][35], cement solidification [36,37], and vitrification [38,39], have all demonstrated efficacy in mitigating contaminant transport in situ. Remediation methods that depend upon chemical transformations for in situ sequestration of contaminants must first consider local geochemical parameters that include local geology, concentrations of soluble anions and cations, pH, and redox state.…”