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

联合国目标7：确保人人获得负担得起、可靠、可持续的现代能源是人类未来面临的主要挑战之一。英国能源研究计划研究委员会将这一问题描述为能源“三难困境”，包括减少排放、加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有前途的解决方案。然而，目前的核能系统由轻水反应堆主导，这对于能源生产所需的增长并不理想，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。这些反应堆的乏燃料在卸载后仍含有约95%的原始能量，并被视为废物。通过关闭核燃料循环来利用乏燃料中剩余的能量，可以提供几乎无限的能源。此外，它可以提供一个有前途的使用钚库存，一个未使用的能源资产，这是从第一次尝试实现封闭的燃料循环在英国的核系统。从经济角度来看，钚库存被视为负担，因为需要有保障的储存。钚的利用可以将这种仍然存在的能源资产转化为经济资产。本可行性研究的目的是评估冻结壁技术在熔盐快堆中的适用性，这是这种高度创新的反应堆的关键技术。熔盐反应堆的堆芯被设计成没有内部容器结构，并且燃料溶解在盐中以在其中达到临界质量。燃料被泵送通过一些外部热交换器，以提取热量并将其转化为电能。少量的燃料盐被连续地供给并从反应堆中取出，以允许在被再循环到堆芯之前从盐中分离出不需要的裂变产物。因此，由于燃料盐是液体，因此在使用之前和之后需要较少的处理，现场燃料和废物的库存较少。建议将3 GWth（1-1.5 GWe）反应堆作为英国60多年核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的，可靠的和可持续的低碳电力供应，可以将经济和社会负担转化为经济资产。发展熔盐反应堆概念的关键技术挑战之一是熔盐在反应堆中预期的操作温度下腐蚀几乎所有材料。MSFR中预期的高中子通量也已知会使结构材料脆化。这项研究的目的是确定是否使用冻结壁技术是可行的方法，保护反应堆容器免受腐蚀攻击，然后我们可以进行进一步的研究设计concepts.To评估冻结壁技术的可行性，湍流热工水力学的3 GWth反应堆容器的数值模型将耦合到容器壁和中子输运的结构模型。耦合模型将使我们能够观察到的区域，其中的电力生产有助于熔融盐的温度，这反过来又会影响盐液相线和固相线之间的界面处的温度。我们将能够确定厚和薄的冻结膜深度的区域，以指定需要多少冷却来保持盐膜以保护材料，并提出设计修改，以稳定流动并减少反应堆高度上预期的强温度梯度的影响。

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.