Feasibility of the use of frozen walls in molten salt fast reactors (MSFR-FW)

联合国目标7给出了未来能源供应的总体挑战：确保所有人都能获得负担得起、可靠、可持续和现代的能源，这是人类未来面临的主要挑战之一。研究理事会英国能源研究计划将这一问题描述为能源“三难困境”，包括减少排放、增强供应安全和降低成本的挑战。颠覆性创新似乎是解决能源“三难困境”的唯一途径。核反应堆技术有可能为这一挑战提供一个有前途的解决方案。然而，目前的核能系统主要是轻水反应堆，这对能源生产所需的增长来说并不理想，因为由于天然铀的使用不足，它们的长期运行是不可持续的。这些反应堆的乏核燃料在卸货并被进一步视为废物时，仍含有约95%的原始能量含量。通过关闭核燃料循环来利用乏燃料中剩余的能量含量，可以提供几乎无限的能源。此外，它还可以提供对钚储备的有前景的利用，这是一种未使用的能量资产，是英国首次尝试在核系统实现封闭燃料循环后遗留下来的。从经济角度来看，由于需要保障储存，钚储存被视为负担。PU的利用可以将这一仍然存在的能量资产转化为经济资产。本可行性研究的目的是评估冻壁技术在熔盐快堆上的适用性，这是这类高度创新的反应堆的关键技术。熔盐反应堆的堆芯设计成没有内部容器结构，燃料溶解在盐中达到临界质量。燃料通过许多外部热交换器泵送，以提取热量并转化为电能。少量的燃料盐不断地从反应堆进料和取出，以便在回收到堆芯之前将不需要的裂变产物从盐中分离出来。因此，由于燃料盐是液体，因此在使用前和使用后需要较少的处理，燃料和废物的现场库存也较少。一个3GWth(1-1.5GWE)反应堆被提议作为英国60多年核能发电积累的乏核燃料的直接燃烧器。因此，MSFR旨在作为一种负担得起、可靠和可持续的低碳电力供应，将经济和社会负担转化为经济资产。开发熔盐反应堆概念的关键技术挑战之一是，熔盐在反应堆预期的运行温度下腐蚀几乎所有材料。MSFR中预期的高中子通量也是众所周知的，它会使结构材料变脆。这项研究旨在确定使用冻壁技术是否是保护反应堆容器免受腐蚀侵蚀的可行方法，然后我们可以继续进行设计概念的进一步研究。为了评估冻壁技术的可行性，将3GWth反应堆容器的湍流热工水力学数值模型耦合到容器壁和中子输运的结构模型。耦合的模型将使我们能够观察到发电量对熔盐温度有贡献的区域，而熔盐温度反过来又会影响盐液相线和固相线界面的温度。我们将能够确定厚层和薄层冻膜深度的区域，以便具体说明维持盐膜以保护材料所需的冷却程度，并提出设计修改方案，以稳定流动并减少反应堆高度上预期的强烈温度梯度的影响。

The overall challenge for the future energy supply is given in UN Goal 7: Ensure access to affordable, reliable, sustainable and modern energy for all is one of the major challenges for the future of human being. The Research Councils UK Energy Research Program describes the problem as the energy 'trilemma' consisting of the challenges to reduce emissions, enhance security of supply, and reducing the cost. Disruptive innovation seems to be the only way to tackle the energy 'trilemma'.Nuclear reactor technologies have the potential to deliver a promising solution for this challenge. However, the current nuclear energy system is dominated by Light Water Reactors which are not ideal for the required growth in energy production, since their long term operation is not sustainable due to the insufficient use of the natural uranium. The spent nuclear fuel from these reactors still contains ~95% of its original energy content when it is unloaded and considered as waste further on. Making use of the energy content remaining in the spent fuel by closing the nuclear fuel cycle can provide an almost unlimited energy resource. In addition, it can provide a promising use of the Pu stockpile, an unused energetic asset, which is a leftover from the first attempt to achieve a closed fuel cycle in the nuclear system in UK. From an economic point of view, the Pu stockpile is seen as burden due to the requirement of safeguarded storage. Pu utilization could transform this still existing energetic asset into an economic asset.The objective of this feasibility study is to assess the applicability of frozen wall technology to molten salt fast reactors which is a key technology for this kind of highly innovative reactors. The core of molten salt reactors is designed such that there are no internal vessel structures and that the fuel dissolved in the salt to achieve a critical mass therein. The fuel is pumped through a number of external heat exchangers to extract the heat to be converted to electrical power. Small quantities of fuel salt are continuously fed and withdrawn from the reactor to allow the separation of unwanted fission products from the salt before being recycled into the core. Consequently, as the fuel salt is liquid, it requires less processing before and after use with smaller on site inventories of fuels and waste. A 3 GWth (1-1.5 GWe) reactor is proposed as a direct burner of the spent nuclear fuel accumulated from 60+ years of nuclear power generation in the UK. Thus, the MSFR is intended as an affordable, reliable and sustainable supply of low carbon electrical power that can convert an economic and social burden into an economic asset. One of the key technical challenges in developing molten salt reactor concepts is that the molten salt corrosively attacks almost all materials at the operating temperatures expected in the reactor. The high neutron flux expected in the MSFR is also known to embrittle structural materials. This study is intended to determine whether the use of frozen wall technology is feasible method of protecting the reactor vessel from corrosive attack, before we can proceed with further studies of design concepts.To assess the feasibility of frozen wall technology, numerical models of the turbulent thermal hydraulics of the 3 GWth reactor vessel will be coupled to structural models of the vessel wall and the neutron transport. The coupled models will enable us to make observations of regions where the power production contributes to the temperature of the molten salt, which in turn will influence the temperature at the interface between the salt liquidus and solidus interfaces. We will be able to determine regions of thick and thin frozen film depths in order to specify how much cooling is required to maintain the salt film to protect the materials and to propose design modifications that can stabilise the flow and reduce the influence of strong temperature gradients expected over the reactor height.