Study of Environmental Chemical Species and Underground Migration Behavior of TRU

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In order to know underground migration of transuranium elements (TRU) which is important for the safety assessment of geologic disposal of high level radioactive wastes, their adsorption behavior onto rocks and hydrolysis reactions were investigated in the present study.(1) For the adsorption behavior of radionuclides onto rocks, experiments were performed with some adsorbates(CsィイD1+ィエD1, SrィイD12+ィエD1, BaィイD12+ィエD1, EnィイD13+ィエD1, AmィイD13+ィエD1, etc. )and typical adsorbents (quartz, rganite, etc. )to study the applicability of the electric double layer model to adsorption reactions of TRU. The measured data were well analyzed by the model and the obtained thermodynamic equilibrium constants were discussed from a systematic point of view for predicting the unknown values.(2)For the improvement of thermodynamic data on hydrolysis and complexation of actinide ions, the solubility measurement and the time-resolved laser induced fluorescence measurement were performed of U(VI) in alkaline solutions, and the hydrolysis constant for UoィイD22ィエD2(OH)ィイD32-(/) 4ィエD3was newly determined, and the coordination properties of U(VI) hydrolysis species were discussed.(3)Furthermore, the hydrolysis constants of actinide ions were analyzed by using an improved hard sphere model in which the effective charges of actinide ions were considered. In addition to ordinary electrostatic interactions, non-electrostatic interactions were found to contribute to the stability of the hydrolysis species of these ions.