To accomplish government's plan of increasing the role of nuclear energy in the future low-carbon United Kingdom's energy sector, new reactors that increase the overall nuclear generating capacity will be built in the forthcoming decades. As obvious as it might sounds, it is of uttermost importance for these new reactors to reach the highest possible safety standards. The proposed piece of work aims at contributing to two of perhaps the most important safety-related areas of research while establishing strong research links with two esteemed overseas research groups active in the areas:

- As the recent events in Fukushima have demonstrated, there is an enormous benefit in being able to provide the necessary cooling of the plant even in absence of any active power. This can be achieved by relying on passive cooling methods that happens as a consequence of natural-occurring phenomena and does not require any active power intervention. In a nuclear plant, passive cooling can be safely and efficiently provided by natural convection. However, effectiveness and reliability of natural convection is significantly difficult to be predicted with accuracy. The research proposed aims at advancing accuracy and reliability of the methods we use to predict the effectiveness of passive cooling. This part of the work will be accomplished by actively collaborating with researchers from the Nuclear Reactors Group of Politecnico di Milano, in Italy.

- Almost all water cooled reactors exploit boiling as a very efficient cooling method. Boiling is a very efficient heat transfer mechanism as long as the heated surface remains wetted by water. Otherwise heat transfer deteriorates dramatically, eventually compromising the integrity of the fuel rods and the safety of the plant. This part of the work deals with our understanding and ability to predict one of the most relevant aspect of boiling flows, which is the behaviour of the bubbles in the bulk of the flow. Main objective is to further develop computational methods available and validate their predictions against bubbly flows as a fundamental step to increase our ability to predict boiling flows. Research will be accomplished by actively collaborating with researchers from the Institute of Fluid Dynamics at Helmholtz-Zentrum Dresden-Rossendorf, in Germany.

Potential Impact:
The present proposal takes advantage and extends research activities funded under the EPSRC UK-India Civil Nuclear Collaboration Phase 2 project "Thermal Hydraulics for Boiling and Passive Systems" (EP/K007777/1) and EPSRC UK-India Civil Nuclear Collaboration Phase 3 project "Grace Time" (EP/M018733/1). Therefore, a direct contribution to the impact envisaged for these two projects is to be expected. Main impact in both is expected from improvement of computational predictive methods available for the design and analysis of new nuclear plants. This will surely benefit from the additional research proposed here as well as from the collaboration with leading overseas groups that are involved in the same research fields. Under the UK-India activities, major contribution to the impact is expected from actively collaborating with researchers at Bhabha Atomic Research Centre (BARC) and engineers at Siemens PLM. Links with these collaborators will be strengthen further by additional excellent research collaborations established by this proposal and the research findings that will be generated and made available to them.

Overall, the availability of more advanced computational tools will increase the capability of designers and regulators to make reliable predictions of natural convection and gas-liquid two-phase flows in nuclear reactor thermal hydraulics. Natural convection directly impacts on passive post-accident cooling of the reactor, whereas gas-liquid bubby flows occur in many reactor flows, including boiling flows, and therefore cooling of fuel rods and other areas of the plant. Therefore, we can expect progress in these areas to directly impact on the ability to develop plants that are safer but at the same time more efficient and, therefore, cheaper and economically-viable in an increasingly competitive energy market.

Safer and cheaper nuclear plants will impact on energy security of the UK and economic prosperity as well through reduced electricity prices. Societal and environmental impact can also be expected from a greater acceptability of nuclear energy as a safe energy source, leading in turn to a reduction in CO2 emissions and the burning of fossil fuels.

Natural convection and bubbly flows are exploited in almost all industrial sectors and engineering applications. Some examples of particular relevance includes energy storage, oil and gas industry, and chemical and pharmaceutical processes such as separation and mixing in bubble columns. Therefore, the proposal carries an extremely high multidisciplinary potential and advances are expected to impact the design of more efficient equipment in these and others industrial and engineering sectors.

Lastly, one additional outcome of the present proposal would be the development of expertise and an increase of research skills in the field of nuclear reactor thermal hydraulics. This area, despite being key to the success of the UK government's nuclear plan, is experiencing a decline in available capabilities in recent decades. The development of individuals with the necessary skills to undertake such work, as well as progress in understanding and predicting key nuclear reactor thermal hydraulic phenomena, can only be enhanced by collaboration with esteemed overseas research groups active in the same areas.