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.