NUclear Fission REactor Thermal-Hydraulics (NUFRETH)

核电一直是英国能源结构的重要组成部分，提供的基本负荷电力约占英国总供应量的21%，是低碳电力的最大单一来源。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大幅增加，同时也需要对一系列其他能源使用进行脱碳处理。核能创新和咨询委员会（NIRAB）建议制定核能计划，以提供至少一半的公司低碳电力，并且核电可以为其他能源部门的脱碳做出贡献。NIRAB的愿景是实现核产品开发的三个流程。大型轻水反应堆（LWR），目前可用，用于基本负荷发电。小型模块化反应堆（SMR），基于相同的技术，增加了灵活性，以满足当地的能源需求。具有更高工作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。在轻水核反应堆技术中，对热工水力学的透彻理解是必不可少的。事实上，水冷核反应堆的设计和安全运行的关键是热量的有效传递，这是通过与冷却水的对流换热来实现的。在一个基本的物理水平上，对流换热的过程是极其复杂的，目前只有部分理解，尽管几十年的广泛研究。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的安全边际，以弥补对热工水力现象的有限理解。热工水力学领域对核反应堆技术至关重要，其中特别需要高分辨率数据来推进基本理解，包括以下方面：1)流动沸腾和两相流：关键的核反应堆技术，在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，并任意外推到瞬态运行条件；2)共轭传热：对于一般的对流传热和结构部件的热疲劳预测至关重要；流动与固体结构之间热耦合的高分辨率研究仍然局限于实验室规模的系统，主要是单相流动；高分辨率的数据在反应堆的代表性尺度上是不可用的；3)流致振动：对于核电站的燃料耐久性和盈利运行至关重要，因为在水冷反应堆中观察到的大部分燃料泄漏是由流致振动引起的微动磨损造成的；很少有文献研究同时测量棒的机械振动和它们周围的流场，没有在反应堆代表的规模和操作条件下；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，但无论是单相传热还是两相传热，都无法在反应堆代表规模上获得高分辨率数据；这些都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.