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For this study, ion-eroded cement was prepared from the cement required for construction of middle- and low-level radioactive waste repositories in caves. The properties for adsorption of 137Cs on cement before and after ion erosion were investigated. XRF, XRD, SEM–EDS and BET were used to analyse various cement materials. The effects of reaction time, solid–liquid ratio, initial radioactivity and different ions on adsorption were studied by static batch experiments. When the initial radioactivity was 1114.5 Bq L−1 and the solid–liquid ratio was 5 g L−1, the adsorption equilibrium time was 12 h. Adsorption of 137Cs on ion-eroded cement was more effective than that on untreated cement. The adsorption process was consistent with the pseudosecond-order kinetic model and the Freundlich isotherm model, and the process involved multilayer chemisorption. This study provides basic research data for construction of a disposal repository. [ABSTRACT FROM AUTHOR]

The adsorption behavior and mechanism of Cs+ on surrounding granite of nuclear waste repository under the groundwater environment were investigated by batch experiments and characterization methods. Results indicate that the adsorption under groundwater environment is inhibited for the presence of other ions, and the adsorbed Cs+ by crushed granite are distributed in the area where K+ is deficient, proving that Cs+ can be captured by granite through ion exchange with K+. This study can provide a key reference for the safety assessment of the repository. [ABSTRACT FROM AUTHOR]

Groundwater is the most important factor contributing to the diffusion and migration of radionuclides in the repository. In this paper, the characteristic parameters of granite in a repository are obtained from static and dynamic experiments to simulate a three-dimensional geological model of the repository with the help of a groundwater modeling system (GMS). It was shown that the longest distances of 137Cs and 60Co migrations for 500 a were 146.66 m and 145.04 m, respectively. This work could be of great significance to ensure the long-term safe operation of this type of waste repository. [ABSTRACT FROM AUTHOR]

Stable mineral colloids play a role in the mobilization of actinide contaminants in the environment. In this paper we present a method to isolate and identify colloids released from high surface area sorbents associated with a proposed clay mineral barrier in a nuclear waste repository. The mineral colloids, which have a strong tendency to remain dispersed in solution, were separated from Al 13 - or (Ce Al)-pillared clay sediment, adsorbed on glass together with hydrolyzed vanadium(IV) species and studied by a variety of techniques including grazing-incidence X-ray scattering (GIXS), small-angle X-ray scattering (SAXS), Fourier transform-infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). We show that the clay platelets are dimensionally orientated in the continuous, transparent 100 nm thick film until the onset of vanadium oxides above 350 °C. Organic matter and the secondary mineral quartz limit the swelling capacity of the platelets, an indication that the stable colloids originate from a part of the native clay that could not be intercalated by aluminum cations. X-ray scattering from oriented clay films intercalated by aluminum- and mixed cerium/aluminum oxo-hydroxy cations are also investigated by the GIXS technique. Unlabelled Image • A continuous, vanadium hydroxide/clay-colloid thin film was self-assembled on glass. • Clay nanoplates dimensionally orient within the 100 nm thick film. • Platelet orientation is preserved until the onset of vanadium oxides above 350 °C. • The platelets are potentially useful for actinide/clay-colloid transport studies. [ABSTRACT FROM AUTHOR]

The Alxa region (Inner Mongolia, China) is one of the areas preselected for use as a geological repository of high-level radioactive waste in China. Radioactive waste produces radioactive rays during long-term storage, and the cumulative absorbed dose in 1000 years can significantly exceed the maximum of 0.7 MGy, thereby challenging the long-term adsorption stability of clay. This study employed 60Co gamma (γ)-rays to irradiate clay in air under a dose rate of 10 kGy/h. The changes in the internal structure and mechanisms of clay under different gamma radiation doses (1, 2, and 3 MGy) were investigated. Additionally, the adsorption properties of irradiated clay for U(Ⅵ) were tested under different conditions. The clay samples underwent minimal structural changes following high-dose irradiation, and the interlayer spacing was altered due to the fractured framework, dehydroxylation, and radiolysis of water. After irradiation, the Fe (Ⅱ) content in clay was significantly increased, unlike Fe (Ⅲ) content. The adsorption mechanisms of clay before and after the experiments were verified, revealing that the adsorption capacity of irradiated clay to U(Ⅵ) is reduced. [Display omitted] • Gamma irradiation caused H 2 O radiolysis and skeleton fracture in clay samples. • The Fe (Ⅱ) content in clay significantly increased after gamma irradiation. • The uranium adsorption capacity of clay decreased after gamma irradiation. • Uranium adsorbed on clay mainly in the form of UO 2 2+. [ABSTRACT FROM AUTHOR]