Towards comprehensive multiphase flow modelling for nuclear reactor thermal hydraulics

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

Abstract

In any nuclear reactor, ensuring that the nuclear fuel always remains properly cooled is the main achievement of the thermal hydraulic design, which thus has utmost impact on the safety and the performance of the plant. Often, this thermal hydraulic design and the plant safety assessment rely on computational models that, by providing a mathematical representation of the physical system, predict the fluid dynamic behaviour of the coolant and the rate of heat transfer in the system. In a nuclear plant, in normal operating conditions or in accident scenarios that require emergency cooling, this often requires solving gas-liquid multiphase flow problems. Unfortunately, although computational tools of any degree of complexity are now available, modelling and computation of gas-liquid multiphase flows is still mainly limited to well-defined flow conditions and/or entirely based on empiricism. The aim of this fellowship is to develop an advanced computational model that overcomes these limitations and goes well-beyond currently available capabilities. At the present time, different techniques reach good accuracy in distinct and well-defined flow conditions, but none has been successful in modelling the entire spectrum of gas-liquid multiphase flows without a priori knowledge of the flow regime. This strongly limits the applicability of available models to flows that are of industrial interest, since these rarely exhibit the same well-characterized and defined flow features. In this project, by means of novel numerical techniques, advanced modelling methods will be coupled in the same computational model and selectively applied based on suitability to the local flow conditions. This will ensure accuracy and unprecedented applicability to multiphase gas-liquid flows, avoiding limiting assumptions but at the same time unrealistic computational requirements.

In the nuclear sector, such a model will provide leading edge modelling and simulation capabilities, underpinning improved operation of the current reactor fleet and design and assessment of future plants. Confident predictions will inform the reactor design and the assessment of safety limits, reducing empiricism and conservatism. In addition, the number of costly experiments will be limited to a smaller number of model-driven tests. Reactors that are safer and produce electricity at a cheaper price and with a reduced waste footprint will underpin Government's plan for between 16 GW and 75 GW of new nuclear generation capacity by 2050. This new capacity will be essential to ensure a secure, sustainable and low-carbon energy future to the UK and respect the legally binding commitment to reduce carbon emission by 2050 of at least 80% with respect to 1990.

In addition, the work will have wider application outside the nuclear sector in the optimization of the design and operation of the numerous industrial equipment exploiting gas-liquid multiphase flows across all branches of engineering (e.g. enhanced mixing by bubbles in bubble columns, fluid dispersion and mass transfer in separation equipment, two/three phase flow streams in extraction, treatment and transportation of oil and gas). At the same time, the fine resolution of spatial and temporal scales as well as of the majority of the interfacial details will allow more fundamental studies to be made. These will shed new light on the many aspects of multiphase flows that still miss thorough understanding, which negatively affects the design and operation of multiphase equipment. The project will benefit from close collaboration with esteemed academics within the UK and overseas (Massachusetts Institute of Technology and North Carolina State University) and industrial leaders in the development of computational products for the nuclear industry and in the analysis and assessment of nuclear reactor thermal hydraulics (Siemens Industry Software Ltd and Frazer-Nash Consultancy).

Planned Impact

The main target of the present fellowship is the modelling capabilities available to the nuclear industry through commercial software packages (e.g. STAR-CCM+) or proprietary models. Recipients include reactor designers (e.g. Rolls-Royce, EDF Energy), regulating bodies (e.g. the Office for Nuclear Regulation) or engineers involved in the analysis and safety assessment of nuclear plants (e.g. Frazer-Nash Consultancy and Wood).
In view of the complexities involved, an all flow-regime multiphase computational model might require decades to reach industrial maturity. However, the organization of the fellowship in work-packages is aimed at delivering impact on different time frames:
- Short-term (3-5 years). Improvements to averaged multi-fluid models (WP 1) that are already best-practice in industry. Timescale can be expected to be comparable to the duration of the fellowship. Impact will be provided on a similar timescale also by availability of high-quality experimental data and high-fidelity simulation results (WP 4) that can support model development and validation.
- Medium term (5-10 years). Improvements to models that track large interfaces, but still model interface transfer processes (WP 3). These models are currently under development and not yet exploited in industry, therefore impact and exploitation on a medium time frame can be reasonably expected.
- Long term (10-20 years). All flow-regime model where large interfaces, and all interface transfers, are fully-resolved. Mainly under conception, these models have the highest potential but might require decades to reach the necessary maturity to be fully-exploited in industry.

Designers will benefit from the availability of more advanced numerical tools that can help improving thermal hydraulic design of reactors, and the level of safety and economic competitiveness of future plants. Using the EPR reactor to be built in Hinkley Point C power station as a reference, an increase of 1% in electricity output (driven by higher efficiency or reduced uncertainty in the safety margins) equals to 350 GWh/year. This translates to around £ 17.5M per year at the current electricity market price. In addition, reliable computational tools can reduce the number of costly experiments to a smaller number of model-driven tests. Examples of the cost of experimental programs are provided by the estimated cost of a UK national thermal hydraulic facility, expected of the order of some tens of million pound sterlings (NIRAB-75-10, 2016), not accounting for operating costs or specific experimental setups.
At the same time, impact is expected on regulators and safety assessors responsible for the safety evaluation of reactors. Accurate predictive models will enable more thorough and less uncertain evaluations of safety margins, potentially limiting conservatism and redundancy of safety systems and benefiting economic viability of reactors, while ensuring the necessary levels of safety are always guaranteed. To put safety in context, continuously increasing estimation for the costs of the Fukushima disaster has been recently set by the Japanese government to $ 187 billion.
Safer plants will improve public acceptability of nuclear energy. In addition, plants that are cheaper to build will reduce investment costs and ensure availability of electricity at more affordable prices, reducing at the same time the CO2 footprint from the energy sector.

Large impact is expected on the developers (e.g. Siemens Industry Software Ltd and ANSYS) of computational fluid dynamic software. By implementing the more advanced models developed in their codes, these companies can make them available to all their users, reaching a number of recipients much larger than the nuclear industry.

Lastly, fellowship will impact on the development of multidisciplinary skills in thermal hydraulics and multiphase flows. In nuclear, these are much needed for United Kingdom's future energy plan to be successful.
 
Description A new advanced computational model for the prediction of multiphase gas-liquid flows has been developed. The model will provide a step change advance in digital tools available to support the development and further optimization of equipment, processes and engineering solutions underpinning low-carbon and sustainable future technologies.
Exploitation Route Starting from the same modelling framework developed, specific versions tailored on multiple engineering and technological applications where multiphase flows are relevant can be developed. Examples include nuclear thermal hydraulics, equipment and processes in chemical and process engineering, biotechnology and biomedical engineering.
Sectors Chemicals,Energy,Environment,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology

 
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: https://doi.org/10.1016/j.nucengdes.2021.111075. 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: https://doi.org/10.1016/j.ces.2021.116520. 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
 
Description North Carolina State University 
Organisation North Carolina State University
Country United States 
Sector Academic/University 
PI Contribution Collaboration in the computational modelling in gas-liquid multiphase flows, providing expertise in the modelling with averaged macroscopic CFD methods
Collaborator Contribution Collaboration in the computational modelling in gas-liquid multiphase flows, providing expertise in the modelling with high-fidelity interface-resolving CFD methods
Impact Joint funding proposal submitted to the US National Science Foundation. Conception of joint funding proposal to be submitted to EPSRC under the Lead Agency Agreement with NSF programme
Start Year 2020
 
Description Indo-UK Civil Nuclear Network Meeting 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Talk on research outcomes at the 2019 Indo-UK Civil Nuclear Network Meeting
Year(s) Of Engagement Activity 2019
 
Description Invited lecture "Computational multifluid modelling of multiphase gas-liquid flows" at North Carolina State University 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Undergraduate students
Results and Impact Lecture given in the Master of Science in Nuclear Engineering program
Year(s) Of Engagement Activity 2020
 
Description Invited presentation at the 3rd UCL OpenFOAM workshop 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk on computational modelling for gas-liquid flows at the 3rd OpenFOAM workshop organized by University College London. The workshop had more than 600 registered attendees from all over the world and with different backgrounds.
Year(s) Of Engagement Activity 2021
 
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 Join CCP NTH and SIG NTH meeting 2020 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Overview of Leeds research in nuclear thermal hydraulics at the joint meeting of the Special Interest Group in Nuclear Thermal Hydraulics and and the Collaborative Computational Project for Nuclear Thermal hydraulics
Year(s) Of Engagement Activity 2020
 
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