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Application of a system thermal-hydraulics code to development of validation process for coupled STH-CFD codes
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.ORCID iD: 0000-0003-1213-0032
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Generation IV reactors are designed to provide sustainable energy generation, minimize waste production and excel in safety. Due to lack of operational experience, ever evolving design and stringent safety requirements, these novel reactors have to rely heavily on simulations.

Best estimate one-dimensional (1D) system thermal-hydraulics (STH) codes, originally intended for simulating water-cooled reactor systems with high coolant mass flow rates, are unable to capture complex three-dimensional (3D) phenomena in liquid metal cooled pool-type reactors. Computational fluid dynamics (CFD) codes are capable of resolving the 3D effects, however applying these methods with high resolution for the whole primary system results in prohibiting computational cost.

At the same time, there are system components where flow can, with reasonable accuracy, be approximated with 1D models (e.g. core channels, some heat exchangers, etc.). One of the proposed solutions in order to achieve adequate accuracy and affordable computational efficiency in modelling of a Generation IV reactor is to divide the primary system into 1D and 3D regions and apply coupled STH and CFD codes on the respective sub-domains.

Successful validation is a prerequisite for application of both, standalone and coupled STH and CFD codes in design and safety analysis of Generation IV systems. In this work we develop and apply different aspects of code validation methodology with an emphasis on (i) STH code analysis in support of validation experiment design (facility and test conditions), (ii) calibration of uncertain code input parameters and validation of standalone STH code, (iii) development of an approach to couple STH and CFD codes.

A considerable part of the thesis work is related to the development of a loop-type, 3 leg, liquid metal experimental facility TALL-3D for code validation. Particular focus was on identification of test conditions featuring complex feedbacks between 1D-3D phenomena, which can be challenging for the codes. Standalone STH code (RELAP5) was validated against experimental data. The domain of natural circulation instabilities in TALL-3D operation parameters was discovered using a validated STH code and global optimum search algorithms. Then existence of growing natural circulation oscillations was experimentally confirmed. An international benchmark was initiated in the framework of EU SESAME project based on the obtained experimental data.

Simulations were performed to define dimensions and location of a new test section for coolant solidification experiments that would also enhance possibilities for studying natural circulation instabilities in the future tests.

An approach to automated input calibration and code validation is developed in order to minimize possible “user effect” in case of multiple uncertain input parameters (UIPs) and system response quantities (SRQs). These methods were applied extensively in the development of RELAP5 input models and identification of the natural circulation instability regions.

Domain overlapping approach to coupling of RELAP5 and Star-CCM+ codes was proposed and resulted in considerable improvement of the predictive capabilities in comparison to standalone RELAP5.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. , p. 68
Series
TRITA-SCI-FOU ; 2018:10
National Category
Engineering and Technology
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-228332ISBN: 978-91-7729-727-7 (print)OAI: oai:DiVA.org:kth-228332DiVA, id: diva2:1209171
Public defence
2018-06-07, FB52, AlbaNova University Center, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20180522

Available from: 2018-05-22 Created: 2018-05-22 Last updated: 2018-05-22Bibliographically approved
List of papers
1. Automation of RELAP5 input calibration and code validation using genetic algorithm
Open this publication in new window or tab >>Automation of RELAP5 input calibration and code validation using genetic algorithm
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2016 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 300, p. 210-221Article in journal (Refereed) Published
Abstract [en]

Validation of system thermal-hydraulic codes is an important step in application of the codes to reactor safety analysis. The goal of the validation process is to determine how well a code can represent physical reality. This is achieved by comparing predicted and experimental system response quantities (SRQs) taking into account experimental and modelling uncertainties. Parameters which are required for the code input but not measured directly in the experiment can become an important source of uncertainty in the code validation process. Quantification of such parameters is often called input calibration. Calibration and uncertainty quantification may become challenging tasks when the number of calibrated input parameters and SRQs is large and dependencies between them are complex. If only engineering judgment is employed in the process, the outcome can be prone to so called "user effects". The goal of this work is to develop an automated approach to input calibration and RELAP5 code validation against data on two-phase natural circulation flow instability. Multiple SRQs are used in both calibration and validation. In the input calibration, we used genetic algorithm (GA), a heuristic global optimization method, in order to minimize the discrepancy between experimental and simulation data by identifying optimal combinations of uncertain input parameters in the calibration process. We demonstrate the importance of the proper selection of SRQs and respective normalization and weighting factors in the fitness function. In the code validation, we used maximum flow rate as the SRQ of primary interest. The ranges of the input parameter were defined based on the experimental data and results of the calibration process. Then GA was used in order to identify combinations of the uncertain input parameters that provide maximum deviation of code prediction results from the experimental data. Such approach provides a conservative estimate of the possible discrepancy between the code result and the experimental data.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Thermal hydraulics
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-185600 (URN)10.1016/j.nucengdes.2016.01.003 (DOI)000372840400019 ()2-s2.0-84958025786 (Scopus ID)
Note

QC 20160428

Available from: 2016-04-28 Created: 2016-04-25 Last updated: 2018-05-22Bibliographically approved
2. The TALL-3D facility design and commissioning tests for validation of coupled STH and CFD codes
Open this publication in new window or tab >>The TALL-3D facility design and commissioning tests for validation of coupled STH and CFD codes
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2015 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 290, p. 144-153Article in journal (Refereed) Published
Abstract [en]

Application of coupled CFD (Computational Fluid Dynamics) and STH (System Thermal Hydraulics) codes is a prerequisite for computationally affordable and sufficiently accurate prediction of thermal-hydraulics of complex systems. Coupled STH and CFD codes require validation for understanding and quantification of the sources of uncertainties in the code prediction. TALL-3D is a liquid Lead Bismuth Eutectic (LBE) loop developed according to the requirements for the experimental data for validation of coupled STH and CFD codes. The goals of the facility design are to provide (i) mutual feedback between natural circulation in the loop and complex 3D mixing and stratification phenomena in the pool-type test section, (ii) a possibility to validate standalone STH and CFD codes for each subsection of the facility, and (iii) sufficient number of experimental data to separate the process of input model calibration and code validation. Description of the facility design and its main components, approach to estimation of experimental uncertainty and calibration of model input parameters that are not directly measured in the experiment are discussed in the paper. First experimental data from the forced to natural circulation transient is also provided in the paper.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-164064 (URN)10.1016/j.nucengdes.2014.11.045 (DOI)000357227700015 ()2-s2.0-84937514619 (Scopus ID)
Note

QC 20150623

Available from: 2015-04-13 Created: 2015-04-13 Last updated: 2018-05-23Bibliographically approved
3. Automated calibration and validationof RELAP5 input model against TALL-3D facility experimental data
Open this publication in new window or tab >>Automated calibration and validationof RELAP5 input model against TALL-3D facility experimental data
(English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759XArticle in journal (Refereed) Submitted
Abstract [en]

Validation of System Thermal Hydraulics (STH) codes against liquid metal facilities is necessary to increase confidence in designing and licensing of generation IV nuclear power systems. Manual input calibration and tuning against a single set of data can lead to bias in the result of the simulation towards specific system configuration and operation regime.In this work we demonstrate an approach to validation of the RELAP5 code, specifically, applicability of RELAP5 to model complex transients from forced to natural circulation in TALL-3D facility with Lead Bismuth Eutectic (LBE) coolant. We utilize an automated approach to (i) calibration of the input model using different experimental data and (ii) quantification of the modelling uncertainties. The automated approach is intended to reduce the effect of the user on the validation outcomes.Results from the calibrated model are compared against an experiment and uncertainty bounds presented. We discuss the results, provide recommendation to the modelling and provide conclusions on the applicability of the RELAP5 to simulation of different transients.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-228330 (URN)
Note

QC 20180522

Available from: 2018-05-22 Created: 2018-05-22 Last updated: 2018-05-22Bibliographically approved
4. Pre-test analysis for identification of natural circulation instabilties in TALL-3D facility
Open this publication in new window or tab >>Pre-test analysis for identification of natural circulation instabilties in TALL-3D facility
2017 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, Vol. 314, p. 110-120Article in journal (Refereed) Published
Abstract [en]

TALL-3D facility is a lead-bismuth eutectic (LBE) thermal-hydraulic loop designed to provide experimental data on thermal-hydraulics phenomena for validation of stand-alone and coupled System Thermal Hydraulics (STH) and Computational Fluid Dynamics (CFD) codes. Pre-test analysis is crucial for proper choice of experimental conditions at which the experimental data would be most useful for code validation and benchmarking. The goal of this work is to identify these conditions at which the experiment is challenging for the STH codes yet minimizes the 3D-effects from the test section on the loop dynamics. The analysis is focused on the identification of limit cycle flow oscillations in the TALL-3D facility main heater leg using a global optimum search tool GA-NPO to find a general region in the parameter space where oscillatory behavior is expected. As a second step a grid study is conducted outlining the boundaries between different stability modes. Phenomena, simulation results and methodology for selection of the test parameters are discussed in detail and recommendations for experiments are provided.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Codes (symbols), Hydraulics, Three term control systems, Computational Fluid Dynamics codes, Experimental conditions, Lead-bismuth eutectics, Natural circulation, Oscillatory behaviors, Parameter spaces, Pre-test analysis, Thermal hydraulics
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-200857 (URN)10.1016/j.nucengdes.2017.01.011 (DOI)000396947800009 ()2-s2.0-85010376003 (Scopus ID)
Note

QC 20170203

Available from: 2017-02-03 Created: 2017-02-03 Last updated: 2018-05-22Bibliographically approved
5. Pre-test analysis of an LBE solidification experiment in TALL-3D
Open this publication in new window or tab >>Pre-test analysis of an LBE solidification experiment in TALL-3D
(English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759XArticle in journal (Refereed) Submitted
Abstract [en]

This paper presents the process of development of a solidification test section design for TALL-3D experimental facility (lead-bismuth eutectic (LBE) thermal-hydraulic loop of prototypic height). Coolant solidification is a phenomenon of potential safety importance for liquid metal cooled fast reactors (LMFRs). Solidification, e.g. in case of excessive performance of the passive decay heat removal systems, can affect local heat transfer and even lead to partial or complete blockage of the coolant flow paths. This might lead to failure of decay heat removal function. In case of reduced flow circulation, the temperature of the coolant will increase, which might prevent complete blockage of the flow. Prediction of possible outcomes of such scenarios with complex interactions between local physical phenomena of solidification and system scale natural circulation behavior is subject to modelling (epistemic) uncertainty. Development and validation of adequate models requires validation grade experimental data. In this work we discuss results of analysis carried out in support experiment development. The aim of the experimental design is to satisfy requirements stemming from the process of qualification of the model that can be used for addressing the safety-related concerns. In this work we focus on two aspects: (i) design of solidification test section (STS) for investigation of local solidification phenomena of lead-bismuth eutectic (LBE), and (ii) effect of the STS on the system scale behavior of the experimental facility. We discuss selection of the STS characteristics and experimental test matrix using computational fluid dynamic (CFD) and system thermal-hydraulic (STH) codes.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-228331 (URN)
Note

QC 20180522

Available from: 2018-05-22 Created: 2018-05-22 Last updated: 2018-05-23Bibliographically approved

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