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.

Since the 2004 Energy Act, nuclear fission has rapidly grown, and continues to grow, in significance in the UK's Energy and Net Zero Strategies. Government's Nuclear Industrial Strategy states clearly that the nuclear sector is integral to increasing productivity, driving growth across the country and meeting our Net Zero target. Nuclear is, and will continue to be, a vital part of our energy mix, providing low carbon power now and into the future, and the safe and efficient decommissioning of our nuclear legacy is an area of world-leading expertise. In order for this to be possible we need to underpin the skill base. The primary aim of SATURN is to provide high quality research training in the science and engineering underpinning nuclear fission technology, focussed on three broad themes: Current Nuclear Programmes. Decommissioning and cleanup; spent fuel and nuclear materials management; geological disposal; current operating reactors (AGRs, Sizewell B, propulsion); new build reactors (Hinkley C, Sizewell C, possibly Wylfa Newydd; Future Nuclear Energy: Advanced nuclear reactors (light water reactors, including PWR3, gas cooled reactors, liquid metal cooled reactors, other concepts); advanced fuel cycles; fusion (remote handling, tritium); Nuclear Energy in a Wider Context: Economics and finance; societal issues; management; regulation; technology transfer (e.g. robotics, sensors); manufacturing; interaction of infrastructure and environment; systems engineering. It has become clear that skills are very likely to limit the UK's nuclear capacity, with over half of the civil nuclear workforce and 70% of Subject Matter Experts due to retire by 2025. High level R&D skills are therefore on the critical path for all the UK's nuclear ambitions and, because of the 10-15 year lead time needed to address this shortage, urgent action is needed now. SATURN is a collaborative CDT involving the Universities of Manchester, Lancaster, Leeds, Liverpool, Sheffield and Strathclyde, which aims to develop the next generation of nuclear research leaders and deliver underpinning (Technology Readiness Level (TRL) 1-3), long term science and engineering to meet the national priorities identified in Government's Nuclear Industrial Vision. SATURN also provides a pathway for mid technology level research (TRL 4-6) to be carried out by allowing projects to be based partly or entirely in an industrial setting. The consortium partners have been instrumental in a series of highly successful CDTs, Nuclear FiRST (2009-2013), NGN (Next Generation Nuclear, 2013-2018) and GREEN (Growing skills for Reliable, Economic Energy from Nuclear, 2018-2023). In collaboration with an expanded group of key nuclear industry partners SATURN will create a step-change in PhD training to deliver a high-quality PhD programme tailored to student needs; high profile, high impact outreach; and adventurous doctoral research which underpins real industry challenges.