Lead Research Organisation: Imperial College London
Department Name: Dept of Mechanical Engineering


Modern computational methods can be a very valuable tool in assessing the behaviour of nuclear power stations, and ensuring that they present minimal hazard to either the public or the environment. This proposal is to fund research further to develop such methods, and by careful comparison of their predictions with actual measurements, establish predictive tools that are appropriate, robust, efficient and validated. The work proposed seeks to achieve this by developing a basis for the verification and validation of computational tools against well-defined benchmark cases. It also seeks to develop advanced computational methods to address problems in normal operation and fault conditions, as well as to investigate aspects of system behaviour in severe accident situations.

Planned Impact

Research outputs of the kind planned are important In view of the central role that nuclear power is expected to play over the next decades. New reactors and reactor types must meet ever higher economic and safety criteria, and assessing their ability to meet these relies more and more on advanced computational modeling. Direct beneficiaries of this will be designers, assessors and operators of nuclear plant,; better analysis tools, properly validated, are essential to realize the continuing benefits of nuclear new build. Society in general will gain too, as it benefits from the economical and carbon-free energy such nuclear plant provide. Adoption within the nuclear industry of new approaches is quite properly cautious, and the impact of the work proposed here will have a range of timescales of application. Better validated CFD models could be employed essentially immediately in (say) licensing assessment (as KNOO-developed methods indeed are as we write), whereas fundamental improvements in (say, just as one example of the research proposed) particulate deposition processes in severe accidents will quite properly take longer to work through. The resurgent nuclear industry (UK, and worldwide, indeed) has an urgent need for trained scientists and engineers, at Doctoral and Postdoctoral level, to undertake these design and assessment activities. Besides the research outputs themselves, programmes like this are valuable in generating such people. The programme proposed is tightly coupled to industry, with significant co-funding, co-location of researchers, and strong industrial collaboration running as a theme through it. This will be effective in ensuring that the research outputs are properly made available to industry, and that their uptake is maximized.


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Description Imperial College
-A detailed analysis has been performed of the alternative approaches to the modelling of buoyant flows in nuclear reactor applications using computation fluid dynamics, and the characteristics of the most appropriate turbulence models have been elucidated.
-Good progress has been made on understanding the software-engineering issues in the coupling of nuclear systems codes and computational fluid dynamics codes, and working tools have been generated.
-Our understanding of the thermal-hydraulic significance of nuclear reactor crud has been increased, and models have been developed to understand its behavior at a microscopic level, and its macroscopic behavior in modifying flows in the core.

-During the CMANP project, a novel numerical method for simulating multi-phase, multi-material flows was developed. This is based on a control volume-finite element mixed formulation and the PnDG-Pn+1 finite element pair that is order n discontinuous across elements for velocity and order n+1 continuous across elements for pressure. This approach enables the use of unstructured meshes that are able to resolve real-life/complex geometries - unlike traditional approach of using structured grids. This method was coupled with the latest anisotropic mesh adaptivity methods. Even though the methods developed here are general purpose they were mostly applied in the field of nuclear safety. Following extensive validation, the model was used to simulate three very specific processes during a severe nuclear accident. These are: 1. fuel pin failure, melt and relocation to the lower vessel head; 2. corium pool behaviour under external cooling and 3. quenching of debris beds.

-Large eddy simulation was successfully interfaced with a new Lagrangian particle tracking approach capable of handling the wide range of particle morphologies (varying from needle-like, through near-spherical to platelets or flakes) and sizes encountered in practice. These techniques have been applied to predicting the transport and deposition of such particles and a generic understanding of how non-spherical particles behave in turbulent flows developed. As originally envisaged, this has included two-way coupling between the flow and the particles, with the effects of sub-grid scale motion accounted for, and the influence of both translational and rotational motions of non-spherical particles accommodated. The simulations have also been applied to systems that replicate the transport of such particles in the reactor core, and their deposition characteristics, with the results of relevance to predicting the build-up of "crud" on boiler tubes or fuel cladding that can have a significant impact on thermal efficiency, fuel performance and overall reactor safety.

-Adaptive wall-functions have been developed for the near-wall elliptic-blending eddy- viscosity model that is particularly efficient at predicting fluid/wall heat transfer and drag. The achievement of the new methodology is to make the predictions of this turbulence model less dependent on the spatial resolution in the viscous, buffer and logarithmic layer of the near-wall flow. It can be used with industrial meshes for which localized areas with fine resolution are embedded into the coarsely meshed full domain
Exploitation Route The methods developed during this project have formed the basis for the UK's multi-phase programme grant MEMPHIS. In addition, these methods form part of Imperial College's open-source CFD code Fluidity that is used worldwide in a range of application areas. Finally, findings on heat transfer patterns for late in-vessel retention during severe nuclear accidents are currently being considered by German colleagues. (Pain, Imperial)

Work on understanding the fundamental heat transfer processes in nuclear fuel crud has been made available to NNL, who now propose to fund us to incorporate, jointly with them, advanced chemistry models. (Walker, Imperial)

Research into coupling nuclear 'systems' codes with CFD is being taken up, with additional support from them, by Rolls Royce. (Walker, Imperial)

The Elliptic Blending model and Adaptive wall-functions for fluid/wall heat flux and friction developed and widely applied during this project have been adopted by EDF R&D and CD Adapco. (Laurence, Manchester)
Sectors Aerospace, Defence and Marine,Energy

Description Advisory committees and/or government reviews During CMANP:_ (i) One investigator has been appointed to the MoD Research Programme Group, responsible for reviewing the MoD programme in the area of nuclear submarine reactor thermal hydraulics. (Walker, Imperial) (ii) One investigator led the nuclear thermal hydraulic area of a DECC-funded review of UK research needs for the future UK nuclear programme. (Walker, Imperial) (iii) One investigator was asked to join a NIRAB group on reactor systems advising NIRAB & DECC on future research needs. (Walker, Imperial) Collaborations & Partnerships Shortly after the CMANP activity was made public, we were approached by a University in Pakistan (PIEAS, Islamabad) to receive three junior members of their academic staff to come to the United Kingdom for three years to undertake Ph.D.'s as part of the CMANP programme. This we did, with three PhD's subsequently gained (Ul Haq, Ahmad, Ilyas), and a continuing collaboration has ensued. (For example, Ahmad from PIEAS has been an Academic Visitor with us for the last few months, returning this March to Pakistan.) (Imperial) Arising from our work on natural circulation modelling, we were approached to host a researcher from Texas A & M University. They had been heavily engaged in building experimental rigs for the measuring these flows, and wished to share our expertise in modelling them. The immediate result was our hosting of a researcher from there for some months, with associated publications. This collaboration is continuing and growing, leading to a recent joint bid for funding in this area; see below. (Imperial) Westinghouse in Sweden approached us over within-core fuel dryout modelling, and this has grown into a fruitful collaboration, involving them and out Pakistan and India collaborators. A joint Indo-Sweden-Pakistan-UK paper has just been submitted. (Imperial) The grant has led to the strengthening of several international collaborations, including Tokyo University (Japan), Narvik University College (Norway). (Imperial) Contact has been established with Dr. Cristian Marchioli of Università di Udine, Italy as a result of the work undertaken on the grant. We are currently discussing the joint application of direct and large eddy simulation techniques to the prediction of the dispersion and deposition of fibre-like particles in turbulent flows. (Leeds) This grant has led to a strong collaboration with AMEC-FW on application of the EdF code Saturne for nuclear severe accidents. (Newcastle) Active member of SARNET (European Severe Accident Network throughout out the entire 3 year program, and continuing. )Application of QMOMC (Conditional Quadrature Method Of Moments) in solving the aerosol agglomeration equation to compare predictions of the aerosol particle growth as validation of the model in the THAI experiments within SARNET Work package 8.2) (Newcastle) Collaboration with Fox's working group in Ecole Centrale, Paris. (Identification and implementation of robust algorithms for treatment of multidimensional moment methods.) Further funding •Work undertaken on the grant is of relevance to, and has led to further funding on, the following grants: •Work under CMANP on the computation of in-vessel flows for nuclear reactors was a major contributor to receiving significant industrial support for research in this and complementary areas. We now have an industry-funded project involving support for six Ph.D. students and a postdoctoral researcher on various aspects of computation of primary circuit nuclear flows. Some of these projects indeed have been aligned directly with activities under the umbrella of the EPSRC Grant. (Imperial). •The CMANP work has grown into a major collaborative activity with the Indian Department of Atomic Energy, with the UK side supported by a series of EPSRC grants, the most recent three of which were announced in the last month. (Imperial, Leeds) •No one grant of itself leads to it, but this grant was part of the portfolio of grants that contributed to the award to Imperial of the Nuclear Energy CDT. (Imperial) •EPSRC UK-Japan collaboration on nuclear safety (Imperial) •In-vessel melt retention (IVMR) a Horizon 2020 consortium lead by IRSN (Imperial) •TSB OCTOPUS project on modelling porous media flows. (Imperial) •Research Councils' Energy Programme, Collaborative Research Programme in Decommissioning, Immobilisation and Management of Nuclear Waste, EPSRC EP/L014041/1, Decommissioning, Immobilisation and Storage Solutions for Nuclear Waste Inventories - DISTINCTIVE (10/02/14-09/02/18). (Leeds) •Research Councils' Energy Programme, Collaborative Research Programme in the Nuclear Fuel Cycle, EPSRC EP/L018616/1, PACIFIC - Providing a Nuclear Fuel Cycle in the UK for Implementing Carbon Reductions (01/03/14-28/02/18). (Leeds) •Technology Strategy Board, Contract 167248, Measurement and Modelling of Sludge Transport and Separation Processes (01/06/13-30/11/15). (Leeds) •Prospective further funding: The Texas A&M collaboration initiated by the CMANP work has led to a recent application for joint US DoE / EPSRC funding on the modelling of passive reactor flows. If the proposal is funded, we have been offered complementary PhD students, supported by both the National Nuclear Lab, and Rolls Royce, to work on this project. (Imperial) •Amec funding for development and application of code SATURNE for Severe Accidents (Newcastle) •EPSRC funded program Frontiers in Engineering Biology (NUFEB) project. (Newcastle) •Rolls-Royce iCASE funding for PGRS on CFD of thermal fatigue is T-junctions of reactor piping systems . (Manchester, Laurence) •CD-Adapco (software vendor) PDRA funding on development and benchmarking of elliptic blending turbulence models for near-wall heat flux and friction simulation on arbitrary meshes (Manchester, Laurence) EDF-Energy EngD x 2 funding for PGRS On the Computational Modelling of Flow and Heat Transfer in In-Line Tube Banks (Manchester, Iacovides) EDF-Energy funding for Computation of Buoyant Flows in Differentially Heated Inclined Cavities (Manchester, Iacovides) EDF-Energy funding for Investigation of heat transfer across AGR boiler insulation sleeves cavities (Manchester, Iacovides) EDF-Energy funding for simulation & experiments on AGR fuel pin pressure drop and heat transfer evolution (Manchester, Iacovides & Laurence)
First Year Of Impact 2011
Sector Aerospace, Defence and Marine,Energy,Government, Democracy and Justice