乏燃料后处理中的辐射化学问题 Ⅱ.水溶液和稀释剂的辐射分解

    Radiation Chemistry in Spent Fuel Reprocessing Ⅱ. Radiolysis of Aqueous Solution and Diluent

    • 摘要: 由于乏燃料具有强辐射性的特点,辐射化学伴随在乏燃料后处理每个过程中。尽管α和γ等电离辐射对于萃取剂本身的直接效应一般不大,但是它们通过与水相和油相中的溶剂相互作用产生的自由基,一方面可以攻击萃取剂的配位基团,另一方面溶剂辐解产生的活性粒种可能与金属离子反应改变其氧化态,从而降低其萃取效率或分配比。水相中硝酸辐解产生的亚硝酸对于金属离子的氧化态会产生重要影响,产生的自由基如•NO3 等也会与萃取剂反应使其劣化。在先进核能系统中,随着燃耗的提高,放射性更强,而且用于溶解乏燃料的硝酸浓度也增高,因而,对于先进核燃料循环中的辐射化学研究既是良好机遇也是重大挑战。本文重点对近十年来国内外在乏燃料后处理(溶剂萃取)方面有关辐射化学研究,特别是硝酸的辐射分解、锕系水溶液的辐射化学、稀释剂的辐射分解等方面进行综述与讨论。

       

      Abstract: Due to the strong radioactivity of spent nuclear fuel, radiation chemistry is accompanied in spent fuel reprocessing. Although the direct effects of ionizing radiation on the extractant itself are usually not significant, the reactive radicals generated by the interaction of ionizing irradiation with the solvent molecules in water or oil phases, may attack the extractant. The transient species produced by solvent radiolysis may react with metal ions and change their oxidation state, resulting in the decrease of their extraction efficiencies or partition ratios. The nitrous acid produced by nitric acid radiolysis in the aqueous phase has an important influence on the oxidation state of the metal ion, and other radicals such as •NO3 also can deteriorate the solvent. In advanced nuclear energy systems, the radioactivity is stronger because of the higher burnup of the nuclear fuel. The concentration of nitric acid used to dissolve spent fuel also increases. Therefore, it is now a good opportunity to carry out radiation chemistry studies for advanced fuel cycles, but obviously with great challenge. This review aims to discuss radiation chemistry related to researches on reprocessing(solvent extraction) in the past decade, especially the radiolysis of nitric acid, the radiation chemistry of actinide aqueous solutions and the radiolysis of diluent.

       

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