电场加速法用于核素迁移参数的获取研究进展

Research Progress on Application of Electric Field Acceleration Method for Acquisition of Nuclide Migration Parameter

  • 摘要: 获取放射性核素在深地质处置环境中的迁移参数是评价地质处置库安全性的核心任务之一。电场加速法(电迁移)可快速、高效获取核素迁移参数,且能与传统批式吸附法和恒定源扩散法等方法相互印证和补充,具有广阔应用前景。本文针对电迁移在核素迁移领域的应用,综述了电迁移获取核素迁移参数的研究进展,介绍了电迁移方法的原理和装置,探讨了电场加速条件下用于获取核素迁移参数的一维无限长柱状模型、栓流模型、对流-弥散模型和等温非线性吸附模型的应用,分析了未来电迁移法的研究方向,以期为全面、深入地应用电场加速法获取核素迁移参数提供理论参考。

     

    Abstract: Deep geological disposal is a feasible scheme for the disposal of high radioactive waste which is generally accepted in the world. The study on migration behaviors of radionuclides and acquisition of relevant parameters, such as distribution coefficient and diffusion coefficient, is one of the core tasks to evaluate the safety of the repository. Compared with batch experiments, the electric field acceleration method (electromigration) does not need to destroy or even crush the samples. Therefore, the obtained adsorption parameters are closer to reality because little chance to increase the solid-liquid contact area in the adsorption processes. Compared with through-diffusion method, the electromigration method can greatly shorten the experiment period for obtaining the diffusion coefficient. In this paper, aiming at the application of electromigration in the field of nuclide migration, the research progress of electromigration method to get nuclide migration parameters was summarized. The principle of electromigration method was comprehensively introduced including the electromigration, electro-osmosis, dispersion and adsorption associated with their mathematical expression, chemical reaction as well. In addition, the use of an electrochemical workstation instead of stabilized voltage supply to provide a constant electric field for the experimental samples was introduced. How to eliminate the influence of water electrolysis on pH of background electrolyte is described as well. Furthermore, the mathematical models for acquiring the migration parameters were also analyzed. The 1D infinite columnar model can get parameters by fitting the profile of nuclide concentration distribution in the sample, but this model requires precise cutting and digestion of the sample, which might increase exposure of researchers to radioactive environments in addition to the difficulty of slicing samples. The plug-flow model can obtain parameters by a linear regression of the late-time data of breakthrough curve of the source cell. Nevertheless, the difference of acquired value might be large due to human subjective factors (i.e., the value depends on how many late-time data are used for simulation). In order to reduce this effect, the advection-dispersion model and isothermal nonlinear adsorption model were developed. In these models, all experimental data would be utilized and the mechanism of electromigration, electro-osmosis, dispersion and adsorption were considered. Among them, the application range of isothermal nonlinear adsorption model is wider, and could elaborate the influence of nonlinear adsorption on breakthrough curves. It can also be regarded as the extension of the convective of the convection-dispersion model. However, at present, no experimental data become available, it is hard to certify that a more advanced model accounting for e.g., absorption kinetics or surface complexation should also be developed. Finally, the future investigations of electromigration method are illustrated on the basis of the current research status, including the experimental contents and model development. This paper potentially provides a fundamental theoretical basis for the sound and in-depth application of electric field acceleration method to obtain nuclide migration parameters.

     

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