Study Of The Interaction Of Polystyrene-polyacrylic Acid Micelles With Radionuclides

The safe disposal of high level radioactive waste（HLRW）is one of the prominent issues facing the use of nuclear technology and the development of nuclear energy worldwide.Deep geological disposal is today the most recognized and feasible solution for high level waste disposal,burying high level waste in a stable geological body several hundred metres deep underground to achieve long-term safe isolation of high-level waste from the biosphere.However,factors such as weathering,geology and warfare may lead to the leakage of radionuclides from deep geological repositories and their migration with groundwater to the near and far fields,threatening the ecological environment and human health.Natural organic matter is widely found in geological media,rich in carboxyl and phenolic groups and other active functional groups,can exist in the form of stable environmental colloids,which will inevitably influence and change the fate and transport behaviour of radionuclides.Therefore,it is necessary to investigate the interaction mechanism between radionuclides and organic matter colloids in depth.The main findings of this thesis are as follows:（1）The interaction of xanthate（FA）colloids with uranyl carbonate（UC）was simulated using quasi-monodisperse flat-head polystyrene-polyacrylic acid（PS-b-PAA）micelles.Given the sensitivity of X-rays to heavy metals,the effect of uranyl carbonate on the structure and stability of PS-b-PAA micelles was characterised using mainly synchrotron X-ray small angle scattering（SAXS）techniques.It was shown that with increasing UC concentration（0～0.5mg/m L）,the PAA molecular chains gradually contracted and the lining of the PAA shell layer increased by a factor of 5.Various techniques showed that UC anions and electronegative PS-b-PAA could form stable carrier colloids（surface potential of about-40 m V）,and on average one PS-b-PAA micelle could adsorb 1200 UC;in the highly mineralized Gansu Beishan groundwater,the adsorption of UC by the carrier colloids decreased slightly,but still could be stable in the near-neutral environment The adsorption of UC by the carrier colloids was slightly reduced in the highly mineralized groundwater of the northern mountains of Gansu,but still stable in a near-neutral environment.The column migration experiments showed that the PS-b-PAA-UC colloid has good mobility and can migrate in porous media.（2）Thorium dioxide（Th O₂）colloidal suspensions with an average diameter of 2.5 nm were synthesised using a hydrothermal method and were only stable in strongly acidic solutions,with Th O₂ colloidal particles beginning to aggregate and settle at p H>5.In near-neutral aqueous solutions,Th O₂ colloidal particles can form complex colloids with PS-b-PAA or FA with good stability（surface potential of-50 m V）.SAXS core-shell and multi-layer structure model fitting analysis shows that as the concentration of Th O₂ particles increases（0～0.01mg/m L）,the PS-b-PAA micelles The intensity of the oscillation peak gradually increased,and the Th O₂ nanoparticles were enriched in the PAA shell layer in the form of aggregated states,and on average one PS-b-PAA micelle could adsorb about 30 Th O₂ nanoparticles.Column migration experiments confirmed that the organocolloids could carry Th O₂ nanoparticles in porous media and no desorption of Th O₂ nanoparticles occurred.The above studies show that the presence of organic matter significantly increases the migration risk of radionuclides.The study methodology and results are important for predicting the transport behaviour of radionuclides in deep geological disposal environments,and may provide new technical approaches for an in-depth understanding of the mechanisms of actinide（ionic and colloidal）-organocolloid interactions in solution.