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

通过核能满足25%的电力需求是英国政府到2050年实现安全和净零能源部门战略的支柱之一。在不久的将来，增加核能装机容量将依赖于建造新的水冷裂变反应堆，该反应堆已占全球运营机队的90%。水冷反应堆依靠沸腾来有效地传递堆芯中产生的大量热量，并为汽轮机发电提供动力。“临界热流密度”(CHF)是对反应堆中可安全产生的最大功率的限制。如果超过，蒸汽的产生速度非常强烈，可能会覆盖受热面(例如，反应堆堆芯中的燃料棒)，从而影响系统的热传递能力。温度可以上升到受热面的融化，使CHF成为反应堆完整性和其放射性库存安全遏制的主要风险。然而，我们对沸腾物理的了解仍然有限，因此我们被迫依赖多年前从全面、昂贵的实验CHF测量中发展出来的经验关联式，以评估反应堆的热极限。由于这些模型的经验性，采用了过于保守的工程裕度，迫使反应堆以预测的CHF极限的~75%的功率运行。在这个项目中，我们将开发基于物理原理的更高保真度的创新沸腾计算模型，并能够实现高精度。有了这些模型，反应堆热限制将以不那么保守的方式建立，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、可靠和无碳的电力。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(~16兆帕)运行条件下CHF的预测，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战略。由于加热和冷却应用约占全球二氧化碳排放量的40%，通过沸腾改善热传递将使许多其他领域受益，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.