Development of versatile liquid metal testing facility for lead-cooled fast reactor technology

液态金属冷却核反应堆是一种先进的核反应堆设计，其中主冷却剂是液态金属，如钠、铅或铅铋混合物。液态金属优良的传热特性，以及在常温和高温下运行液态金属反应堆的可能性，是液态金属冷却堆相对于水冷堆设计的主要优点。这些优势导致了更小、更安全的反应堆设计，特别适合小型模块化结构。液态金属冷却核反应堆最初是为船舶推进而开发的，目前正在研究用于发电。特别是，在第四代国际论坛确定的六种核反应堆设计中，目前正在研究短期商业应用的两种是液态金属反应堆：钠冷却快堆和铅冷却快堆。目前的研究重点是铅冷快堆技术。铅冷却的核反应堆将部署在小型模块化装置中，具有长寿命的预制堆芯，在更换之前可以运行数年，因此这些反应堆也适用于不打算建造自己的核基础设施的新兴和发展中国家。液态铅优良的传热能力，加上其高沸点，保证了反应堆关闭后的衰变热可以完全被动地消散，从而产生了特别安全的核反应堆设计。铅也非常致密，因此可以很好地屏蔽伽马辐射，这对保护操作人员和环境是一个额外的好处。钠与空气接触会燃烧，与水接触会爆炸，而铅与空气或水都不会发生明显反应，这使得系统设计更简单、成本更低，工厂运行更安全。目前，铅冷却核反应堆技术的主要缺点是，在核反应堆运行的代表温度下，暴露在液态铅中的材料的侵蚀和腐蚀的知识非常有限。这是本研究旨在解决的知识差距：将在核反应堆运行条件下在液态铅中进行侵蚀和腐蚀试验，以确定最有希望实现反应堆结构部件的材料。实验装置的高保真CFD模拟将首先协助实验设施的设计，然后提供关于局部流场和热场的缺失信息，这对于充分理解实验数据的含义以及将实验结果更广泛地应用于铅冷堆的腐蚀/侵蚀分析是必要的。此外，本研究还将开发一种基于超声波的成像技术，用于检查反应堆运行过程中的内部。事实上，液态金属是不透明的，因此传统的成像技术不适用。对反应堆内部进行定期检查的可能性对于安全和有益的运行是必不可少的。

Liquid-metal-cooled nuclear reactors are advanced nuclear reactor designs where the primary coolant is a liquid metal, such as sodium, lead or a lead-bismuth mixture. The excellent heat transfer properties of liquid metals, and the possibility to operate liquid metal reactors at ambient pressure and very high temperature, are the main advantages of liquid metal cooled reactors with respect to water-cooled reactor designs. These advantages result in smaller and much safer reactor designs, particularly suited for small-modular construction.Originally developed for marine propulsion, liquid-metal-cooled nuclear reactors are currently being investigated for power production. In particular, two out of the six nuclear reactor designs identified by the Generation IV International Forum and currently being researched for near-term commercial application are liquid metal reactors: the sodium-cooled fast reactor and the lead-cooled fast reactor.The present research study, in particular, is focused on the lead-cooled fast reactor technology. Lead-cooled nuclear reactors will be deployed in small and modular units featuring long-life, pre-manufactured cores that can run for several years before being replaced, thus making these reactors also suitable for emerging and developing countries that do not plan to build their own nuclear infrastructure. The excellent heat transfer capabilities of liquid lead, together with its high boiling point, assure that decay heat after reactor shutdown can be safely dissipated with entirely passive means, thus resulting in a particularly safe nuclear reactor design. Lead is also very dense and therefore a good shield against gamma radiations, which is a bonus for protecting the operators and the environment. Unlike sodium that burns in contact with air and that can explode in contact with water, lead does not react significantly with either air or water, allowing simpler and cheaper system design and a safer plant operation.Currently, the main drawback of the lead-cooled nuclear reactor technology is the very limited knowledge of erosion and corrosion of materials exposed to liquid lead at temperatures representative of nuclear reactor operation. This is the knowledge gap that the present research aims to address: erosion and corrosion tests will be carried out in liquid lead at nuclear reactor operating conditions to identify the most promising materials to realize the reactor structural components. High-fidelity CFD simulations of the experimental setup, will first assist with the design of the experimental facility and then provide the missing information on the local flow and thermal fields, necessary to fully understand the implications of the experimental data and apply the experimental findings more widely to corrosion/erosion analysis of lead-cooled reactors.Additionally, the present research will also develop an imaging technology based on ultrasounds to inspect the reactor internals during operation. Liquid metals, in fact, are opaque and conventional imaging techniques therefore not applicable. The possibility to periodically inspect the reactor internals is essential for safe and profitable operation.