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好处，英国或其他地方可能需要在本世纪末实施封闭式核燃料循环。封闭式燃料循环是指从用过的核燃料中回收吖系元素，再循环为先进反应堆的新燃料的循环。在英国，这种回收是通过Purex(钚-铀氧化还原提取)过程实现的。这涉及几个阶段：(I)前端阶段，包括乏燃料在硝酸中的溶解；以及(Ii)分离阶段，即用溶剂萃取法从酸性溶液中分离放线元素。(Iii)精炼阶段，将分离出的元素转化为纯铀和钚产品。闭合循环具有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。英国正在寻求开发先进的燃料循环，以在经济、安全、防扩散、可持续性和灵活性方面提高标准，在分离过程中提供进一步的优势。这导致了“高级纯铀”工艺的概念，它可以通过循环使用传统的以铀为基础的燃料和/或新的铀/钚混合氧化物(MOX)燃料来生产混合(U、Pu)和纯U产品。然而，使用过的高钚燃料--如高燃耗UO2和基于MOX的燃料--溶解的一个关键问题是存在不溶的富钚颗粒，这需要在前端阶段采用比仅由硝酸提供的更激进的溶解方法。其中一种方法涉及使用强大的氧化剂，如银(II)，以氧化方式溶解燃料的富钚区域。该项目与英国国家核实验室(NNL)合作，将提供支持这种燃料溶解过程的实验证据，主要目的是了解氧化态物种，如银(II)或臭氧如何溶解燃料，以及作为氧化溶解过程中潜在干扰物的不溶性裂变产物(例如，Ru、Pd、铂、Rh、Mo)的存在可能如何影响这一点。使用新的、先进的真实燃料模拟器(所谓的SIMFUELs)，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，结果将通报和补充在NNL中心实验室进行的真实乏燃料研究。

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.