\mathrmReO_4^- 和Cs+在完整北山花岗岩中的迁移特性

    Migration Properties of \mathrmReO_4^- and Cs+ in Intact Beishan Granites

    • 摘要: 深地质处置是国内外普遍认可的高放废物处置方法。关键核素在处置库围岩介质中的迁移参数的获取是深地质处置安全评价的重要组成部分。本工作以北山新场地区的花岗岩为研究对象,采用改进的电迁移装置研究了Cs+和\mathrmReO_4^- 在北山花岗岩中的扩散和吸附特性(在研究核素的迁移特性时,铼常被用作锝的替代物),获取不同电压条件下Cs+和\mathrmReO_4^-在完整北山花岗岩中的穿透曲线。此外,建立了基于一级吸附动力学的对流-弥散模型以更精确地解释实验数据。采用新模型估算的\mathrmReO_4^- 和Cs+在完整北山花岗岩中的有效扩散系数 D_\mathrmm^\mathrme 分别为(4.68±0.15)×10−13 m2/s和(4.85 ± 0.94)×10−14 m2/s,与文献报道的结果相近,吸附分配系数Kd分别为(9.92±0.07)×10−7 m3/kg和(5.52±0.2)×10−5 m3/kg,表明铼在北山花岗岩上几乎不吸附。

       

      Abstract: Deep geological disposal is a widely recognized method for the disposal of high-level radioactive waste both domestically and internationally. The acquisition of migration parameters for key nuclides in the host rock medium of disposal repositories is a crucial component of safety assessments for deep geological disposal. Traditional experimental methods suffer from drawbacks such as lengthy testing periods and the need to crush rock samples. The electro-migration method employed in this study enables ions to rapidly migrate toward the opposite direction of the electrodes under the influence of an electric field, allowing for the rapid acquisition of breakthrough curves for ions in intact granite, thereby effectively addressing the shortcomings of traditional experimental methods. In the model processing, this study employs first-order kinetic adsorption advection-dispersion modeling. While considering the effects of electro-migration, electro-osmosis, and diffusion—three important mechanisms—the model also incorporates the influence of dynamic adsorption, resulting in more accurate experimental results. This study focuses on granite from the Beishan Xinchang region, using an improved electro-migration device to investigate the diffusion and adsorption characteristics of Cs+ and \mathrmReO_4^- in Beishan granite(rhenium is often used as a substitute for technetium when studying the migration characteristics of nuclides). During the experiments, we utilized the i-t mode of the electrochemical workstation to precisely control the voltage applied to the rock samples(±0.001 V) and continuously recorded the current flowing through the apparatus. The electrolyte solutions in the anode and cathode chambers were pumped to an external container via a peristaltic pump for mixing, then added dropwise to the cathode and anode chambers, respectively, to prevent short circuits and overflow in the device. We added a small amount of sodium bicarbonate to the background solution to provide \mathrmHCO_3^- and \mathrmCO_3^2- ion buffers, maintaining the stability of the pH gradient in the background solution and adjusting its pH to weakly alkaline(pH=7.8) to simulate the actual groundwater environment of Beishan. We used the electro-migration method to obtain the penetration curves of Cs+ and \mathrmReO_4^- in intact Beishan granite under different voltage conditions. First-order kinetic adsorption advection-dispersion modeling was employed to more accurately interpret the experimental data. Using the new model, the effective diffusion coefficients D_\mathrmm^\mathrme of \mathrmReO_4^- and Cs+ in intact Beishan granite under the absence of an electric field were estimated to be (4.68±0.15)×10−13 m2/s and (4.85±0.94)×10−14 m2/s, which are consistent with previously reported results. The adsorption distribution coefficients(Kd) were (9.92±0.07)×10−7 m3/kg and (5.52±0.2)×10−5 m3/kg, respectively, indicating that rhenium is barely adsorbed on Beishan granite.

       

    /

    返回文章
    返回