Reliable computational modelling of boiling for high-void and the critical heat flux

核能满足25%的电力需求是英国政府到2050年实现安全和净零英国能源部门战略的支柱之一。在不久的将来，增加核装机容量将依赖于建造新的水冷裂变反应堆，这已经占全球运营船队的90%。水冷反应堆依靠沸腾来有效地传递堆芯产生的大量热量，并为蒸汽涡轮机提供动力发电。“临界热通量”（CHF）是对反应堆中可以安全产生的最大功率的限制。如果超过，则蒸汽产生的速率是如此强烈以至于其可以覆盖加热表面（例如，反应堆堆芯中的燃料棒），损害了系统的传热能力。温度可能会上升到加热表面熔化，使CHF成为反应堆完整性和放射性物质安全控制的主要风险。然而，我们的知识的物理沸腾仍然是有限的，因此，我们被迫依赖经验的相关性，开发多年前从全面的，昂贵的实验CHF测量，反应堆的热极限的评估。由于这些模型的经验性质，采用了过于保守的工程裕度，并且反应堆被迫在仅为预测CHF极限的~75%的功率下运行。在本项目中，我们将开发基于物理原理并具有高精度的更高保真、创新的沸腾计算模型。有了这些模型，反应堆的热极限将以更少的保守性建立，使反应堆能够在更高的功率水平下运行，并为我们未来的社会提供负担得起的，可靠的和无碳的电力。该项目将具体改进核反应堆热工水力学的两个关键领域：压水堆高压下CHF的预测（~ 16 MPa）的运行条件，以及核反应堆容器的外部被动冷却，这是缓解罕见但危险的反应堆事故进展的关键策略。加热和冷却应用占全球二氧化碳排放量的40%左右，通过沸腾传热的改进将有益于许多其它领域，例如高功率密度电子设备中的冷却和微冷却应用。在这些领域，设备和效率的进步和进一步改进将取决于该项目将开发的先进和可靠的建模能力的可用性。

Meeting 25% of the electricity demand by nuclear energy is one of the pillars of the UK government's strategy for a secure and net-zero UK energy sector by 2050. In the near future, increasing nuclear installed capacity will rely on building new water-cooled fission reactors, which already represents 90% of the worldwide operating fleet. Water-cooled reactors rely on boiling to efficiently transfer the large amount of heat produced in the core and power the steam turbine generating electricity. The "critical heat flux" (CHF) is a limit on the maximum amount of power that can be safely generated in the reactor. If exceeded, the rate of steam generation is so intense that it can blanket the heating surface (e.g., the fuel rods in the reactor core), compromising the heat transfer capabilities of the system. Temperatures can increase up to the melting of the heating surface, making CHF a major risk to the integrity of the reactor and the safe containment of its radioactive inventory. However, our knowledge of the physics of boiling is still limited, and we are therefore forced to rely on empirical correlations, developed years ago from full-scale, expensive experimental CHF measurements, for the assessment of the reactor thermal limits. Due to the empirical nature of these models, overly conservative engineering margins are adopted, and reactors are forced to operate at a power that is only ~75% of the predicted CHF limit.In this project, we will develop higher-fidelity, innovative computational models of boiling built from physical principles and capable of high accuracy. With these models, reactor thermal limits will be established with less conservatism, enabling reactors to operate at higher power levels and provide affordable, reliable and carbon-free electricity to our future society. The project will specifically improve two key areas of nuclear reactor thermal hydraulics: prediction of CHF at pressurized water reactor high pressure (~ 16 MPa) operating conditions, and external passive cooling of the nuclear reactor vessel, a key strategy to mitigate the progression of rare but dangerous reactor accidents.With heating and cooling applications responsible for around 40% of global CO2 emissions, improvements in heat transfer through boiling will benefit many other sectors, such as cooling and micro-cooling applications in high power density electronics. In these areas, advancement and further improvement of equipment and efficiency will be dependent on the availability of the advanced and reliable modelling capabilities that this project will develop.