Ruthenium: Nuclear's Volatile Problem

Ru是一种裂变产物，具有两种寿命相对较长的稳定同位素：Ru-103(半衰期=39.8天)和Ru-106(半衰期=1年)。这两种同位素都存在于英国的乏燃料中，因此必须在燃料的后处理或处置过程中进行解释。在乏燃料处理的多个阶段，Ru可能暴露在高硝酸、高温条件下，可能导致其以四氧化二Ru的形式转移到气相中。两个这样的阶段是在后处理开始时将乏燃料溶解到浓硝酸中，以及在后处理发生后将Ru玻璃化成玻璃废料。应避免挥发，因为生成的气相Ru可能会重新沉积在工厂其他地方的金属管道内，然后必须进行净化。然而，Ru的挥发发生在出人意料的低温下。虽然在900摄氏度以下，RuO2不会挥发，但在低至150摄氏度的温度下，Ru在硝酸中的溶液中可以析出气态Ru氧化物，这使得Ru在后处理和玻璃化过程中的管理变得困难。因此，由于Ru的挥发性和高比放射性，Ru对核工业有效地管理其消减提出了强大的挑战。关键的挑战是充分了解高度复杂的溶液/固态化学物质，这些化学物质不仅在与溶解器、蒸发器和玻璃化工厂相关的条件下获得，而且在其清理过程中使用的去污染方法中也是如此。使用化学、分析和工程方法的组合，我们将在这个博士学位中寻求解决这些挑战。PHD的具体目标将是：1)开发重量、质谱学、电化学和光谱分析方法，以提高对高硝酸环境中Ru形态和氧化/热处理过程中Ru形态相互转化的理解。2)使用这些方法，建立Ru(III)到Ru(IV)和Ru(VIII)和Ru(IV)到Ru(Viii)之间相互转化的动力学。3)确定Ru(III)络合对这些相互转化的影响以及RuO2在支持或抑制挥发方面的作用。4)建立其他裂变产物金属离子如Ce(IV)可能被氧化从而潜在地挥发Ru(III)的机制。5)研究关键的NOx物种，如NO和HNO2可能对Ru(III)直接氧化或抑制Ce(IV)驱动的Ru(III)氧化的作用。

Ruthenium is a fission product possessed of two relatively long lived stable isotopes: Ru-103 (half life = 39.8 days) and Ru-106 (half life = 1 year). Both isotopes are present in UK spent fuel and so have had to be accounted for during the reprocessing or disposal of that fuel. At a number of stages during the processing of spent fuel, ruthenium can be exposed to high nitric acid, high temperature conditions that may lead to its transfer into the gas phase as ruthenium tetroxide. Two such stages are the dissolution of spent fuel into concentrated nitric acid at the start of reprocessing, and the vitrification of ruthenium into a glass waste form after reprocessing has occurred.Volatilisation is to be avoided as the resultant gas phase ruthenium may then redeposit within metal pipework elsewhere in the plant which will then have to be decontaminated. However, ruthenium volatilisation occurs at unexpectedly low temperatures. Whilst RuO2 is not seen to volatilise below 900oC, gaseous ruthenium oxides have been seen to evolve from solutions of Ru in nitric acid at temperatures as low as 150oC - making the management of ruthenium difficult during reprocessing and vitrification.Thus, given its volatile nature and high specific radioactivity ruthenium presents a strong challenge to the nuclear industry in effectively managing its abatement. Key challenges are to fully understand the highly complex solution/solid state chemistries that obtain not only under conditions relevant to dissolvers, evaporators and vitrification plants, but also in the decontamination methods used in its clean up. Using a combination of chemical, analytical and engineering approaches, we shall seek to address these challenges in this PhD. The specific objectives of the PhD will be to:1) Develop gravimetric, mass spectroscopic, electrochemical and spectroscopic analytical methods that will improve the understanding of ruthenium speciation in high nitric acid environments and oxidation state interconversion during oxidative / thermal treatment of same.2) Using these methods, to establish the kinetics of interconversion between ruthenium species, most especially Ru(III) to Ru(IV) and Ru(VIII) and Ru(IV) to Ru(VIII), and the resultant product distributions of these processes.3) To establish the influence that Ru(III) complexation may have on these interconversions and the role that RuO2 may have in supporting or inhibiting volatilisation.4) Establish the mechanism by which other fission product metal ions such as Ce(IV) may oxidise and thus potentially volatilise ruthenium.5) Investigate the role that key NOx species such as NO and HNO2 may have on oxidising Ru(III) directly or inhibiting the putative Ce(IV)-driven oxidation of Ru(III).