高放废物包装容器铁基材料的Cl吸附腐蚀微观机理研究

Corrosion mechanism of iron-based materials adsorption Cl in high level radioactive waste packaging containers

铁基材料的Cl吸附腐蚀行为研究对高放废物包装容器选材具有指导意义。基于密度泛函第一性原理,构建了Fe(100)表面对Cl的单独吸附和共吸附模型,通过对吸附过程中的吸附能、Fe−Cl键长和电子结构等参数的研究,重点分析了水辐射分解产物(O、H和OH自由基)对Cl吸附的稳定性影响。结果表明:表面缺陷和自由基均会引起Fe−Cl键长的缩短,4种共吸附体系Fe/(Cl−H2O)、Fe/(Cl−H)、Fe/(Cl−OH)、Fe/(Cl−O)的吸附能依次减小,Bader电荷转移数依次增大。表明辐射环境中的缺陷Fe表面对Cl的吸附更稳定,H_(2)O的辐射分解产物促进了缺陷Fe(100)表面对Cl的吸附,揭示了辐射-含氯地下水耦合环境中铁基材料腐蚀的微观机理。

[Background]The packaging container is critical to the safe disposal of high-level radioactive waste.The study of Cl adsorption and corrosion behavior of iron-based materials is of guiding significance for the selection of packaging materials for high-level radioactive waste.[Purpose]This study aims to clarify the effect of Cl adsorption on the corrosion of iron-based materials in radiation environment.[Methods]Based on the first principle of density functional theory,the separation and co-adsorption models of Cl on Fe(100)surface were constructed.Parameters,such as ariations of adsorption energy,Fe−Cl bond length and electronic structure,etc.,in the process of Cl adsorption were studied by using Medea-VASP code.Effects of water radiation decomposition products(O,H and OH free radicals)on the stability of Cl adsorption were analyzed emphatically.[Results]The calculation results show that the length of Fe−Cl bond is shortened by the absence of surface atoms and the existence of free radicals.In the four co-adsorption systems,the adsorption energies of Fe/(Cl−H_(2)O),Fe/(Cl−H),Fe/(Cl−OH)and Fe/(Cl−O)decrease successively,while the charge transfer number of Bader increase successively.[Conclusions]Adsorption of Cl on the defect Fe surface is more stable in the radiation environment,and the radiation decomposition products of H2O promote the adsorption of Cl on the defect Fe(100)surface,revealing the microscopic mechanism of corrosion of iron-based materials in the radiation-chlorine-containing groundwater coupling environment.