Department of Civil and Environmental Engineering, Vanderbilt University, Nashville, TN 37235, United States.
Department of Civil and Environmental Engineering, Vanderbilt University, Nashville, TN 37235, United States; Shanghai Shaanxi Coal Hi-tech Research Institute Co., Ltd., Shanghai 201613, China.
J Hazard Mater. 2023 May 5;449:131004. doi: 10.1016/j.jhazmat.2023.131004. Epub 2023 Feb 13.
Evaluation of the long-term retention mechanisms and potential release rates for the primary constituents of potential concern (COPCs) (i.e., Tc, I, Se, and nitrate) is necessary to determine if Cast Stone, a radioactive waste form, can meet performance objectives under near-surface disposal scenarios. Herein, a mineral and parameter set accounting for the solubility of I and Se in Cast Stone was developed based on pH-dependent and monolithic diffusion leaching test results, to extend a geochemical speciation model previously developed. The impact of oxidation and carbonation as environmental aging processes on the retention properties of Cast Stone for primary COPCs was systematically estimated. Physically, the effective diffusion coefficients of 4 COPCs in Cast Stone were increased after carbonation and/or oxidation, reflecting an increase in permeability to diffusion. Chemically, i) pH & pe conditions in the original Cast Stone were favorable for the stabilization of Tc, but not for I, Se, and N; ii) oxidation (with/without carbonation) of Cast Stone changed the pe & pH conditions to be detrimental for Tc stabilization; and iii) carbonation (with/without oxidation) of Cast Stone modified the pH & pe conditions to be beneficial for the stabilization of I (in system with Ag added) and Se.
评估潜在关注的主要成分（COPCs，即 Tc、I、Se 和硝酸盐）的长期保留机制和潜在释放率对于确定 Cast Stone（一种放射性废物形式）是否能够满足近地表处置场景下的性能目标是必要的。在此，基于 pH 依赖性和整体扩散浸出试验结果，开发了一种考虑 Cast Stone 中 I 和 Se 溶解度的矿物和参数集，以扩展先前开发的地球化学形态模型。系统地估计了氧化和碳化等环境老化过程对 Cast Stone 保留主要 COPC 的特性的影响。物理上，COPCs 的有效扩散系数在碳化和/或氧化后在 Cast Stone 中增加，这反映了扩散渗透性的增加。化学上，i）原始 Cast Stone 的 pH 和 pe 条件有利于 Tc 的稳定，但不利于 I、Se 和 N；ii）Cast Stone 的氧化（有/无碳化）改变了 pe 和 pH 条件，不利于 Tc 的稳定；iii）Cast Stone 的碳化（有/无氧化）改变了 pH 和 pe 条件，有利于添加 Ag 时 I 和 Se 的稳定。
