Computational modelling for nuclear reactor thermal hydraulics

Lead Research Organisation: University of Leeds
Department Name: Chemical and Process Engineering


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.

Planned 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.
Description The work funded allowed establishing research collaborations with Helmholtz-Zentrum Dresden-Rossendorf in Germany and Politecnico di Milano in Italy. These collaborations enabled joint research programs to be conceived and accomplished. Research work further developed and improved the digital software tools available to model bubbly flows and natural circulation in closed loops, areas in which the collaborating institutions bring world leading expertise. These are key to nuclear reactor thermal hydraulics and impact the safety and the performance of nuclear reactors under development or in operation. the tools developed will be available to engineers, designers and regulators responsible for the analysis and the assessment of the design of nuclear reactors and many other industrial equipment in multiple industrial and engineering sectors.
Exploitation Route Research findings have been disseminated in the academic community through publications and specific invited seminars in the participating institutions. The award has led to 5 publications, with at least one additional journal paper and one additional conference paper expected in the second part of 2021. Modelling improvements have been implemented in software of large use and these improvements will be available to engineers and modelers working in the nuclear sector and in other relevant areas across the energy sectors, to which more accurate and robust digital modelling tools will be beneficial. In a similar way, modelling improvements will be also available to CFD software developers for implementation in their proprietary commercial code that reach a wide user community across multiple industrial and engineering sectors. It is important to note how the funding allowed establishing collaboration still ongoing that are expected to continue producing impact on the identified areas in near future.
Sectors Energy

Description Towards comprehensive multiphase flow modelling for nuclear reactor thermal hydraulics
Amount £345,425 (GBP)
Funding ID EP/S019871/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 08/2019 
End 08/2022
Description Collaboration with HZDR in computational modelling of bubbly flows 
Organisation Helmholtz Association of German Research Centres
Department Helmholtz-Zentrum Dresden-Rossendorf
Country Germany 
Sector Academic/University 
PI Contribution Collaboration was started under travel grant EP/R045194/1 and is now supported by the Fellowship award EP/S019871/1. Multiple visits were made to Helmoholtz-Zentrum Dresden-Rossendorf (HZDR). I provided expertise in multiphase modelling and implementation of additional turbulence modelling capabilities in HZDR multifluid OpenFOAM solver. I also provided simulation results for common benchmark for multiphase bubbly flows.
Collaborator Contribution Expertise in multiphase modelling with multifluid CFD methods. Access to HZDR multifluid OpenFOAM solver. Simulation results for common benchmark for multiphase bubbly flows.
Impact Advanced CFD multifluid model for the prediction of gas-liquid multiphase flows Joint publications: M. Colombo, R. Rzehak, M. Fairweather, Y. Liao, D. Lucas, 2021. Benchmarking of computational fluid dynamic models for bubbly flows. Nuclear Engineering and Design 375, 111075. DOI: M. Colombo, R. Rzehak, M. Fairweather, Y. Liao, D. Lucas, 2019. Benchmarking of CFD modelling closures for two-phase turbulent bubbly flows. 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 18), Portland, USA, August 18-24.
Start Year 2018
Description Collaboration with Politecnico di Milano 
Organisation Polytechnic University of Milan
Country Italy 
Sector Academic/University 
PI Contribution Visits to Politecnico di Milano. Expertise in CFD modelling of natural circulation instabilities. Computational resources at University of Leeds
Collaborator Contribution Expertise in nuclear thermal hydraulics and natural circulation instabilities. Experimental data from DYNASTY experimental facility on natural circulationn installed at Politecnico di Milano. Visiting student spending 3 months at the University of Leeds.
Impact Advanced CFD model for the prediction of natural circulation flow instabilities Joint publications: A. Battistini, A. Cammi, S. Lorenzi, M. Colombo, M. Fairweather, 2021. Development of a CFD - LES model for the dynamic analysis of the DYNASTY natural circulation loop. Chemical Engineering Science, 116520. DOI: C. Introini, A. Battistini, A. Cammi, S. Lorenzi, M. Colombo, M. Fairweather, 2020. Requirements of LES modelling in natural circulation loops: Preliminary study in a pipe geometry. 29th International Conference Nuclear Energy for New Europe, Portoroz, Slovenia, September 7-10.
Start Year 2019
Title Advanced CFD model for the prediction of natural circulation flow instabilities 
Description Advanced solver for the computational fluid dynamic prediction of flow instabilities in natural circulation loops, including conjugate heat transfer through the loop walls and large-eddy simulation for the prediction of turbulence in the fluid. 
Type Of Technology Software 
Year Produced 2020 
Open Source License? Yes  
Impact The solver can improve the understanding of natural circulation instabilities in flow loops and provide more accurate predictions of stable operating regimes in passive cooling loops installed in nuclear plants or designed to be operated in new generation reactors, such as the moltern salt reactor. 
Title Advanced CFD multifluid model for the prediction of gas-liquid multiphase flows 
Description Advanced multifluid solver based on the reactingEulerFoam family of OpenFOAM solvers. Solver have been developed jointly by HZDR and University of Leeds, with University of Leeds specifically developing the multiphase turbulence modelling section of the solver. 
Type Of Technology Software 
Year Produced 2019 
Open Source License? Yes  
Impact The CFD model makes available a more advance tool for the prediction of multiphase gas-liquid flows. This will impact capabilities to predict different multiphase scenarios in nuclear reactors, including boiling, improving efficiency and safety of the reactors. In more general, model is applicable to improve the analysis of multiphase flows in all engineering applications and industrial equipment. 
Description Invited seminar "Computational modelling of boiling and passive cooling for nuclear reactor thermal hydraulics" at North Carolina State University 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Research work was presented in an invited seminar at the Nuclear Engineering Department of North Carolina State University in the United States. The seminar was attended by around 50 people, including academic members, young researchers, postgraduate and undergraduate students. Seminar allowed disseminating research findings across the academic community of one of the more prestigious nuclear engineering department in the United States, and world leader in the research areas of mutual interest. Seminar will be used as a starting point for the development of future collaboration.
Year(s) Of Engagement Activity 2020
Description Invited seminar at Helmholtz-Zentrum Dresden-Rossendorf 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Invited seminar "Modelling and simulation of two-phase, boiling and buoyancy-driven flows" given at Helmholtz-Zentrum Dresden-Rossendorf. Research findings were disseminated across the academic comunity from the institute.
Year(s) Of Engagement Activity 2018
Description UKFN SIG in Nuclear Thermal hydraulics 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Meeting of the UKFN SIG in Nuclear Thermal Hydraulics was organziedat the University of Leeds and included specific talks on ongoing EPSRC funded research. The audience included around 50 delegates from other Uk universities, industry and the office for nuclear regulation
Year(s) Of Engagement Activity 2019