镧锕分离用含氮软配体的辐射稳定性研究进展

    Radiolytic Stability of N-Donor Soft Ligands for Actinide(Ⅲ)/Lanthanide(Ⅲ) Separation

    • 摘要: 含氮软配体对次锕系元素(MA)配位能力强、选择性高,其在MA与镧系元素(Ln)分离中具有良好的应用前景。鉴于高放废液的强放射性和高硝酸浓度,为实现工艺长期运行的安全性和稳定性,体系中所有化学组分必须耐受强辐射环境。目前对于含氮软配体的辐射稳定性仍存在很大的争议。本文概述了近年来关于三嗪类单吡啶衍生物(BTP)、三嗪类双吡啶衍生物(R-BTBP)及三嗪类邻啡啰啉衍生物(R-BTPhen)等含氮软配体的γ辐射及α辐射稳定性相关研究,介绍了分子结构、剂量率、两相接触、氧含量等因素对配体γ辐射稳定性的影响。不同的辐射实验条件及辐射体系组成都可能导致不同的降解路径和降解率,且采用60Co源模拟辐射工况,可能会夸大或低估辐射效应的影响。总结了辐射稳定性研究中存在的问题,并展望了该领域的重点研究方向。

       

      Abstract: The waste from nuclear power plants worldwide has to be isolated from humans and his environment for about 100 000 years to equal the levels of natural uranium. If, however, the long-lived actinides could be separated from the spent fuel and transmuted, then the isolation time could be shortened to about 1 000 years. It is known that one class of N-containing soft ligands has excellent extraction ability and selectivity for minor actinides (MA), the separation of MA/lanthanides(Ln) from high level waste has been expected. One of the limiting points to ensure a safe and stable long-term operation is the resistance against radiation of all chemicals involved in the systems due to the highly radioactive field and high nitric acid concentration. Derivatives of 2,6-bis(1,2,4-triazine-3-yl)pyridine(BTP), 6,6'-bis(1,2,4-triazin-3-yl)-2,2'-bipyridine(R-BTBP) and 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline(R-BTPhen) were widely employed for trivalent minor actinoid and lanthanoid separation in the promising innovative Selective Actinide Extraction(i-SANEX) and Grouped Actinide Extraction(EURO-GANEX) processes. However, researches towards radiolytic stability of these N-donor ligands presented controversial results. Herein, researches on stability against γ-radiation or α-radiation of R-BTP, R-BTBP, R-BTPhen and 2,6-bis1H-1,2,3-triazol-4-yl-pyridine(PyTri) at different experimental conditions and solvent formulations are reviewed. In most cases, γ irradiations were performed using 60Co sources and α irradiation were performed using 241Am or 244Cm solution. The effects of molecular structure, dose and dose rate, contact between phases, oxygen content, different phase composition, acidity, diluent and phase modifier on the γ-radiation stability of these ligands are introduced. The performance and changes in the composition have been analyzed during the irradiation experiment by different techniques, such as Raman spectroscopy, HPLC-MS and ICP-MS, to determine the degradation of the organic or aqueous solvents. These data were used to provide critical insight into the fundamental radiolysis mechanisms responsible for the radiolytic stability of ligands. In general, degradation was slower in the presence of both organic and aqueous phases during irradiation for both the hydrophobic and hydrophilic ligands. However, different experimental conditions and solvent formulations may lead to different degradation paths and degradation rates, and these experimental results are not comparable. Moreover, it is generally accepted that simulate radiation conditions, usually 60Co, may exaggerate or underestimate the influence of radiation effects. The controversial results obtained demonstrate the importance of developing realistic irradiation experiments where different factors affecting the performance can be easily studied and isolated. The existing problems in the study of radiolytic stability are summarized, and the key research directions in this field are prospected.

       

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