NUclear Fission REactor Thermal-Hydraulics (NUFRETH)

核电一直是英国能源结构的重要组成部分，提供的基荷电力约占英国总供应量的21%，是最大的单一低碳电力来源。英国政府承诺到2050年实现净零碳排放，这将导致电力需求的逐步增加，以及一系列其他能源使用的脱碳需求。核能创新和咨询委员会（NIRAB）建议，核能计划至少提供一半的公司低碳电力，而且核能可以促进其他能源部门的脱碳。NIRAB的愿景是核产品开发的三个流。目前可用于基荷发电的大型轻水反应堆。小型模块化反应堆（SMR），基于相同的技术，具有更大的灵活性，以满足当地的能源需求。具有更高运行温度的先进模块化反应堆（AMR）也有助于其他能源部门的脱碳。全面了解热工水力学对于轻水核反应堆技术至关重要。事实上，水冷核反应堆的设计和安全运行的关键是有效的传热，这是通过与冷却剂水的对流传热来实现的。在基本的物理水平上，对流传热过程极其复杂，尽管进行了数十年的广泛研究，但目前仅部分了解。因此，即使是已建立的反应堆技术也需要在其设计中纳入惩罚性安全裕度，以弥补对热工水力现象的有限理解。对核反应堆技术至关重要的热工水力学领域，其中特别需要高分辨率数据来推进基本的理解，包括以下内容：1）流动沸腾和两相流：关键的核反应堆技术，这里的基本理解是如此有限，以至于分析和建模仍然严重依赖于低分辨率的经验相关性，从稳态数据中提取并任意外推到瞬态操作条件; 2）共轭热传递：对于一般对流热传递和结构部件的热疲劳预测至关重要;流动和固体结构之间的热耦合的高分辨率研究仍然限于实验室规模的系统，主要是单相流动;在反应堆代表性规模上没有高分辨率数据;3）流动诱导振动：对于核电站的燃料耐久性和盈利性操作至关重要，因为由流动引起的振动导致的微动磨损是水冷反应堆中观察到的大多数燃料泄漏的原因;很少有文献记载的研究既测量棒的机械振动又测量棒周围的流场，没有一项研究是在反应堆代表性的规模和操作条件下进行的; 4）自然对流被动冷却回路：被动冷却在核反应堆技术中至关重要，但在反应堆代表性尺度上，无论是单相还是两相传热，都没有高分辨率的数据;这些是本研究旨在解决的知识差距。

Nuclear power has been a vital part of the UK's energy mix, providing baseload electricity at around 21% of the UK's total supply, the largest single source of low carbon power. The UK government's commitment for net zero carbon emissions by 2050 will lead to a step increase in electricity demand, as well as the need to decarbonise a range of other energy uses. The Nuclear Innovation and Advisory Board (NIRAB) advises to plan for nuclear energy to provide at least half of the firm low carbon electricity and also that nuclear power can contribute to the decarbonisation of other energy sectors. NIRAB's vision is for three streams of nuclear product development. Large-scale Light Water Reactors (LWR), currently available, for baseload electricity generation. Small Modular Reactors (SMR), based on the same technology for additional flexibility to meet local energy needs. Advanced Modular Reactors (AMR), with higher operating temperatures, to also contribute to the decarbonisation of other energy sectors.A thorough understanding of thermal-hydraulics is essential in light-water nuclear reactor technology. In fact, key to the design and safe operation of water-cooled nuclear reactors is the effective transfer of heat, which is achieved by convective heat transfer to and from the coolant water. At a fundamental physical level, the process of convective heat transfer is extremely complex and only partially understood at present, despite decades of extensive investigations. As a consequence, even established reactor technologies need to incorporate penalizing safety margins into their design, in order to compensate for the limited understanding of thermal-hydraulics phenomena. Thermal-hydraulics areas crucial to nuclear reactor technology where high-resolution data are particularly needed to advance the fundamental understanding include the following:1) Flow boiling and two-phase flow: Crucial nuclear reactor technology, here the fundamental understanding is so limited that the analysis and modelling still heavily rely on low-resolution empirical correlations, distilled from steady-state data and arbitrarily extrapolated to transient operating conditions;2) Conjugate heat transfer: Crucial for convective heat transfer in general and for thermal fatigue prediction in structural components; the high-resolution investigation of the thermal coupling between flows and solid structures is still restricted to laboratory-scale systems and mainly to single-phase flows; high-resolution data are not available at a reactor-representative scale;3) Flow-Induced vibration: Crucial for fuel durability and profitable operation of nuclear power stations, because the fretting wear that results from flow-induced vibration is responsible of the majority of fuel leaks observed in water-cooled reactors; very few documented studies measure both the mechanical vibration of the rods and the flow field around them, none at reactor-representative scale and operating conditions;4) Natural convection passive cooling loops: Passive cooling is of vital importance in nuclear reactor technology, yet high-resolution data are not available at a reactor-representative scale, either for single phase or two-phase heat transfer;These are the knowledge gaps that the present research aims to address.