The electrochemistry of Ag(II) and its application in spent fuel dissolution

为了最大限度地发挥近零碳核能的效益，封闭式核燃料循环可能需要在英国或本世纪晚些时候在其他地方实施。封闭式燃料循环是指从使用过的核燃料中回收锕系元素，再循环为先进反应堆的新燃料。在英国，这种回收是通过PUREX（钚-铀氧化还原提取）工艺进行的。这涉及几个阶段：（i）头端阶段，涉及将乏燃料溶解在硝酸中;和（ii）分离阶段，其中通过溶剂萃取将锕系元素从酸溶液中分离出来。(iii)分离出的锕系元素转化为纯铀和钚产品的最后阶段。封闭循环具有最大限度地减少高放射性废物和最大限度地利用天然铀资源的潜在优势。联合王国正在寻求开发先进的燃料循环，在分离过程中提供进一步的优势，提高经济、安全、防扩散、可持续性和灵活性方面的标准。这就产生了“先进PUREX”工艺的概念，该工艺可以通过再循环传统的氧化铀基燃料-尽管操作时铀的使用量较高或“燃耗”较高-和/或新的铀/钚混合氧化物燃料来生产混合（铀、钚）和纯铀产品。然而，溶解使用过的高钚含量燃料（例如高燃耗UO 2和MOX基燃料）的一个关键问题是存在不溶性富钚颗粒，这需要在头端阶段采用比单独使用硝酸更积极的溶解方法。一种这样的方法涉及使用强力氧化剂如银（II）来氧化溶解燃料的富钚区域。该项目与英国国家核实验室（NNL）合作，将提供实验证据来支持这种燃料溶解过程，主要重点是了解氧化物质（如银（II）或臭氧）如何溶解燃料，以及不溶性裂变产物的存在如何影响燃料溶解（例如Ru、Pd、Pt、Rh、Mo）作为氧化溶解过程中的潜在干扰物。使用新的、先进的真实的燃料模拟物（所谓的SIMFUEL），实验工作将主要在兰开斯特的UTGARD（铀-钍β-伽马活性研发）实验室进行，其结果将为在NNL中央实验室进行的真实的乏燃料研究提供信息和补充。

To maximise the benefits of near-zero carbon nuclear energy, closed nuclear fuel cycles may need to be implemented in the UK or elsewhere later this century.Closed fuel cycles are those in which actinides are recovered from used nuclear fuel for recycling into new fuels for advanced reactors. In the UK, this recovery was effected by the PUREX (Plutonium-Urananium Redox EXtraction) process. This involves several stages:(i) The headend stage, involving the dissolution of the spent fuel in nitric acid; and (ii) The separations stage where the actinides are separated from the acid solution by solvent extraction.(iii) The finishing stage where the separated actinides are converted to pure U and Pu products.Closed cycles offer the potential advantages of minimising high level wastes and maximising use of natural uranium resources. The UK is seeking to develop advanced fuel cycles that offer further advantages in separation processes with enhanced standards in economics, safety, proliferation resistance, sustainability and flexibility. This has led to the concept of an "Advanced PUREX" process that can produce a mixed (U,Pu) and a pure U product by recycling either conventional uranium oxide-based fuels - albeit operated to higher uranium usage or "burnup" - and/or new uranium/plutonium mixed oxide (MOX) fuels to. However, a key issue in the dissolution of used high plutonium content fuels - such as high burnup UO2 and MOX based fuels - is the presence of insoluble plutonium rich particles that require more aggressive dissolution methods at the headend stage than those offered by nitric acid alone. One such method involves the use of powerful oxidising agents such as silver(II) to oxidatively dissolve the Pu-rich regions of the fuel. This project, a collaboration with the UK's National Nuclear Laboratory (NNL), will provide experimental evidence to support such a fuel dissolution process, with the main focii being on understanding how oxidising species such silver(II) or ozone dissolve fuel, and how this may be impacted upon by the presence of insoluble fission products (e.g. Ru, Pd, Pt, Rh, Mo) as potential interferrants in the oxidative dissolution process. Using new, advanced simulants for real fuels (so-called SIMFUELs), experimental work will be conducted primarily in Lancaster's UTGARD (Uranium-Thorium beta-Gamma Active R&D) Lab, with results informing and complementing studies on real spent fuel conducted at NNL's Central Laboratory.