The Experts below are selected from a list of 7824 Experts worldwide ranked by ideXlab platform

Emilio Baglietto - One of the best experts on this subject based on the ideXlab platform.

  • improved delayed detached eddy simulation of a randomly stacked nuclear Pebble Bed
    Computers & Fluids, 2015
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract The high temperature reactor (HTR) design concept exhibits excellent safety features due to the low power density and the large amount of graphite present in the core which gives a large thermal inertia in the event of an accident such as loss of coolant. However, the possible appearance of hot spots in a Pebble Bed core design may affect the integrity of the Pebbles and the fuel. This has drawn the attention of several scientists to understand this highly three-dimensional complex phenomenon. To obtain accurate predictions based on techniques such as DNS and LES, for a realistic (even for a small size) Pebble Bed flow, is still computationally too expensive and not foreseeable in the near future. On the other hand, the prediction capabilities of turbulence modelling approaches such as RANS and hybrid RANS-LES methods for such complex flow regime have not yet been rigorously evaluated. In this paper, numerical simulations of a limited sized randomly stacked Bed of spherical Pebbles are performed by using improved delayed detached eddy simulation (IDDES). The Pebble Bed configuration analysed consists of approximately 30 Pebbles, which are randomly stacked to represent the core of an HTR. The obtained results are compared (qualitatively and quantitatively) with the available reference LES for validation purposes. The results show that the selected IDDES based on the SST k-ω model is able to reproduce the overall flow topology. The mean flow and thermal fields are found to be in good agreement with the LES. However, the second order statistics have shown significant disagreement. Nevertheless, these results are explicitly discussed in detail to understand the flow and thermal fields appearing in this complex flow configuration.

  • Numerical simulation of nuclear Pebble Bed configurations
    Nuclear Engineering and Design, 2015
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract High Temperature Reactors (HTRs) are being considered all over the world. An HTR uses helium gas as a coolant, while the moderator function is taken up by graphite. The fuel is emBedded in the graphite moderator. A particular inherent safety advantage of HTR designs is that the graphite can withstand very high temperatures, that the fuel inside will stay inside the graphite Pebble and cannot escape to the surroundings even in the event of loss of cooling. Generally, the core can be designed using a graphite Pebble Bed. Some experimental and demonstration reactors have been operated using a Pebble Bed design. The test reactors have shown safe and efficient operation, however questions have been raised about possible occurrence of local hot spots in the Pebble Bed which may affect the Pebble integrity. Analysis of the fuel integrity requires detailed evaluation of local heat transport phenomena in a Pebble Bed, and since such phenomena cannot easily be modelled experimentally, numerical simulations are a useful tool. As a part of a European project, named Thermal Hydraulics of Innovative Nuclear Systems (THINS), a benchmarking quasi-direct numerical simulation (q-DNS) of a well-defined Pebble Bed configuration has been performed. This q-DNS will serve as a reference database in order to evaluate the prediction capabilities of different turbulence modelling approaches. A wide range of numerical simulations based on different available turbulence modelling approaches are performed and compared with the reference q-DNS. This paper reports a detailed comparison of LES, Hybrid (RANS/LES) and RANS models with the reference q-DNS. These simulations are performed for a well-defined single face cubic centred Pebble configuration. The obtained flow and thermal fields are extensively analyzed to understand the flow physics in such complex flow regime. Furthermore, lessons learned from these simulations are summarized in the form of guidelines for such complex flow configurations. In addition, following these guidelines, a strategy has been developed to perform large eddy simulations of a realistic limited sized random Pebble Bed.

  • quasi direct numerical simulation of a Pebble Bed configuration part i flow velocity field analysis
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract High temperature reactors (HTR) are being considered for deployment around the world because of their excellent safety features. The fuel is emBedded in a graphite moderator and can sustain very high temperatures. However, the appearance of hot spots in the Pebble Bed cores of HTR's may affect the integrity of the Pebbles. A good prediction of the flow and heat transport in such a Pebble Bed core is a challenge for available turbulence models and such models need to be validated. In the present article, quasi direct numerical simulations (q-DNS) of a Pebble Bed configuration are reported, which may serve as a reference for the validation of different turbulence modeling approaches. Such approaches can be used in order to perform calculations for a randomly arranged Pebble Bed. Simulations are performed at a Reynolds number of 3088, based on Pebble diameter, with a porosity level of 0.42. Detailed flow analyses have shown complex physics flow behavior and make this case challenging for turbulence model validation. Hence, a wide range of qualitative and quantitative data for velocity and temperature field have been extracted for this benchmark. In the present article (part I), results related to the flow field (mean, RMS and covariance of velocity) are documented and discussed in detail. Moreover, the discussion regarding the temperature field will be published in a separate article.

  • quasi direct numerical simulation of a Pebble Bed configuration part ii temperature field analysis
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract Good prediction of the flow and heat transfer phenomena in the Pebble Bed core of a high temperature reactor (HTR) is a challenge for available turbulence models, which still require to be validated. While experimental data are generally desirable in this validation process, due to the complex geometric configuration and measurement difficulties, a very limited amount of data is currently available. On the other hand, direct numerical simulation (DNS) is considered an accurate simulation technique, which may serve as an alternative for validating turbulence models. In the framework of the present study, quasi-direct numerical simulation (q-DNS) of a single face cubic centered Pebble Bed is performed, which will serve as a reference for the validation of different turbulence modeling approaches in order to perform calculations for a randomly arranged Pebble Bed. These simulations were performed at a Reynolds number of 3088, based on Pebble diameter, with a porosity level of 0.42. Results related to flow field (mean, RMS and covariance of velocity) have been presented in Part-I, whereas, in the present article, we focus our attention to the analysis of the temperature field. A wide range of qualitative and quantitative data for the thermal field (mean, RMS and turbulent heat flux) has been generated.

  • numerical simulations of a Pebble Bed configuration using hybrid rans les methods
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract A High Temperature Reactor (HTR) is envisaged to be one of the reactor designs to play a role in nuclear power generation including process heat applications. The HTR design concept exhibits excellent safety features due to the low power density and the large amount of graphite present in the core which gives a large thermal inertia in the event of an accident such as loss of coolant. However, the possible appearance of hot spots in the Pebble Bed cores of HTR may affect the integrity of the Pebbles. This has drawn the attention of several scientists to understand this highly three-dimensional complex phenomenon. To obtain accurate predictions based on techniques such as DNS and LES, for a realistic Pebble Bed flow, is still computationally too expensive and not foreseeable in the near future. On the other hand the prediction capabilities of turbulence modeling approaches such as RANS and hybrid RANS–LES methods for such complex flow regime have not yet been rigorously evaluated. In the present study, numerical simulations of a single cubic Pebble Bed configuration using hybrid RANS–LES methods are presented. Various delayed detached eddy simulation (DDES) methods based on Spalart–Allmaras and k–ω SST models are used for the calculations. Moreover, an extensive qualitative and quantitative comparison has been performed between the obtained results and available quasi-DNS data. Results are found to be in good agreement and support the use of hybrid (RANS/LES) for such type of complex flow configurations.

Afaque Shams - One of the best experts on this subject based on the ideXlab platform.

  • improved delayed detached eddy simulation of a randomly stacked nuclear Pebble Bed
    Computers & Fluids, 2015
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract The high temperature reactor (HTR) design concept exhibits excellent safety features due to the low power density and the large amount of graphite present in the core which gives a large thermal inertia in the event of an accident such as loss of coolant. However, the possible appearance of hot spots in a Pebble Bed core design may affect the integrity of the Pebbles and the fuel. This has drawn the attention of several scientists to understand this highly three-dimensional complex phenomenon. To obtain accurate predictions based on techniques such as DNS and LES, for a realistic (even for a small size) Pebble Bed flow, is still computationally too expensive and not foreseeable in the near future. On the other hand, the prediction capabilities of turbulence modelling approaches such as RANS and hybrid RANS-LES methods for such complex flow regime have not yet been rigorously evaluated. In this paper, numerical simulations of a limited sized randomly stacked Bed of spherical Pebbles are performed by using improved delayed detached eddy simulation (IDDES). The Pebble Bed configuration analysed consists of approximately 30 Pebbles, which are randomly stacked to represent the core of an HTR. The obtained results are compared (qualitatively and quantitatively) with the available reference LES for validation purposes. The results show that the selected IDDES based on the SST k-ω model is able to reproduce the overall flow topology. The mean flow and thermal fields are found to be in good agreement with the LES. However, the second order statistics have shown significant disagreement. Nevertheless, these results are explicitly discussed in detail to understand the flow and thermal fields appearing in this complex flow configuration.

  • Numerical simulation of nuclear Pebble Bed configurations
    Nuclear Engineering and Design, 2015
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract High Temperature Reactors (HTRs) are being considered all over the world. An HTR uses helium gas as a coolant, while the moderator function is taken up by graphite. The fuel is emBedded in the graphite moderator. A particular inherent safety advantage of HTR designs is that the graphite can withstand very high temperatures, that the fuel inside will stay inside the graphite Pebble and cannot escape to the surroundings even in the event of loss of cooling. Generally, the core can be designed using a graphite Pebble Bed. Some experimental and demonstration reactors have been operated using a Pebble Bed design. The test reactors have shown safe and efficient operation, however questions have been raised about possible occurrence of local hot spots in the Pebble Bed which may affect the Pebble integrity. Analysis of the fuel integrity requires detailed evaluation of local heat transport phenomena in a Pebble Bed, and since such phenomena cannot easily be modelled experimentally, numerical simulations are a useful tool. As a part of a European project, named Thermal Hydraulics of Innovative Nuclear Systems (THINS), a benchmarking quasi-direct numerical simulation (q-DNS) of a well-defined Pebble Bed configuration has been performed. This q-DNS will serve as a reference database in order to evaluate the prediction capabilities of different turbulence modelling approaches. A wide range of numerical simulations based on different available turbulence modelling approaches are performed and compared with the reference q-DNS. This paper reports a detailed comparison of LES, Hybrid (RANS/LES) and RANS models with the reference q-DNS. These simulations are performed for a well-defined single face cubic centred Pebble configuration. The obtained flow and thermal fields are extensively analyzed to understand the flow physics in such complex flow regime. Furthermore, lessons learned from these simulations are summarized in the form of guidelines for such complex flow configurations. In addition, following these guidelines, a strategy has been developed to perform large eddy simulations of a realistic limited sized random Pebble Bed.

  • quasi direct numerical simulation of a Pebble Bed configuration part i flow velocity field analysis
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract High temperature reactors (HTR) are being considered for deployment around the world because of their excellent safety features. The fuel is emBedded in a graphite moderator and can sustain very high temperatures. However, the appearance of hot spots in the Pebble Bed cores of HTR's may affect the integrity of the Pebbles. A good prediction of the flow and heat transport in such a Pebble Bed core is a challenge for available turbulence models and such models need to be validated. In the present article, quasi direct numerical simulations (q-DNS) of a Pebble Bed configuration are reported, which may serve as a reference for the validation of different turbulence modeling approaches. Such approaches can be used in order to perform calculations for a randomly arranged Pebble Bed. Simulations are performed at a Reynolds number of 3088, based on Pebble diameter, with a porosity level of 0.42. Detailed flow analyses have shown complex physics flow behavior and make this case challenging for turbulence model validation. Hence, a wide range of qualitative and quantitative data for velocity and temperature field have been extracted for this benchmark. In the present article (part I), results related to the flow field (mean, RMS and covariance of velocity) are documented and discussed in detail. Moreover, the discussion regarding the temperature field will be published in a separate article.

  • quasi direct numerical simulation of a Pebble Bed configuration part ii temperature field analysis
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract Good prediction of the flow and heat transfer phenomena in the Pebble Bed core of a high temperature reactor (HTR) is a challenge for available turbulence models, which still require to be validated. While experimental data are generally desirable in this validation process, due to the complex geometric configuration and measurement difficulties, a very limited amount of data is currently available. On the other hand, direct numerical simulation (DNS) is considered an accurate simulation technique, which may serve as an alternative for validating turbulence models. In the framework of the present study, quasi-direct numerical simulation (q-DNS) of a single face cubic centered Pebble Bed is performed, which will serve as a reference for the validation of different turbulence modeling approaches in order to perform calculations for a randomly arranged Pebble Bed. These simulations were performed at a Reynolds number of 3088, based on Pebble diameter, with a porosity level of 0.42. Results related to flow field (mean, RMS and covariance of velocity) have been presented in Part-I, whereas, in the present article, we focus our attention to the analysis of the temperature field. A wide range of qualitative and quantitative data for the thermal field (mean, RMS and turbulent heat flux) has been generated.

  • numerical simulations of a Pebble Bed configuration using hybrid rans les methods
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract A High Temperature Reactor (HTR) is envisaged to be one of the reactor designs to play a role in nuclear power generation including process heat applications. The HTR design concept exhibits excellent safety features due to the low power density and the large amount of graphite present in the core which gives a large thermal inertia in the event of an accident such as loss of coolant. However, the possible appearance of hot spots in the Pebble Bed cores of HTR may affect the integrity of the Pebbles. This has drawn the attention of several scientists to understand this highly three-dimensional complex phenomenon. To obtain accurate predictions based on techniques such as DNS and LES, for a realistic Pebble Bed flow, is still computationally too expensive and not foreseeable in the near future. On the other hand the prediction capabilities of turbulence modeling approaches such as RANS and hybrid RANS–LES methods for such complex flow regime have not yet been rigorously evaluated. In the present study, numerical simulations of a single cubic Pebble Bed configuration using hybrid RANS–LES methods are presented. Various delayed detached eddy simulation (DDES) methods based on Spalart–Allmaras and k–ω SST models are used for the calculations. Moreover, an extensive qualitative and quantitative comparison has been performed between the obtained results and available quasi-DNS data. Results are found to be in good agreement and support the use of hybrid (RANS/LES) for such type of complex flow configurations.

Ferry Roelofs - One of the best experts on this subject based on the ideXlab platform.

  • improved delayed detached eddy simulation of a randomly stacked nuclear Pebble Bed
    Computers & Fluids, 2015
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract The high temperature reactor (HTR) design concept exhibits excellent safety features due to the low power density and the large amount of graphite present in the core which gives a large thermal inertia in the event of an accident such as loss of coolant. However, the possible appearance of hot spots in a Pebble Bed core design may affect the integrity of the Pebbles and the fuel. This has drawn the attention of several scientists to understand this highly three-dimensional complex phenomenon. To obtain accurate predictions based on techniques such as DNS and LES, for a realistic (even for a small size) Pebble Bed flow, is still computationally too expensive and not foreseeable in the near future. On the other hand, the prediction capabilities of turbulence modelling approaches such as RANS and hybrid RANS-LES methods for such complex flow regime have not yet been rigorously evaluated. In this paper, numerical simulations of a limited sized randomly stacked Bed of spherical Pebbles are performed by using improved delayed detached eddy simulation (IDDES). The Pebble Bed configuration analysed consists of approximately 30 Pebbles, which are randomly stacked to represent the core of an HTR. The obtained results are compared (qualitatively and quantitatively) with the available reference LES for validation purposes. The results show that the selected IDDES based on the SST k-ω model is able to reproduce the overall flow topology. The mean flow and thermal fields are found to be in good agreement with the LES. However, the second order statistics have shown significant disagreement. Nevertheless, these results are explicitly discussed in detail to understand the flow and thermal fields appearing in this complex flow configuration.

  • Numerical simulation of nuclear Pebble Bed configurations
    Nuclear Engineering and Design, 2015
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract High Temperature Reactors (HTRs) are being considered all over the world. An HTR uses helium gas as a coolant, while the moderator function is taken up by graphite. The fuel is emBedded in the graphite moderator. A particular inherent safety advantage of HTR designs is that the graphite can withstand very high temperatures, that the fuel inside will stay inside the graphite Pebble and cannot escape to the surroundings even in the event of loss of cooling. Generally, the core can be designed using a graphite Pebble Bed. Some experimental and demonstration reactors have been operated using a Pebble Bed design. The test reactors have shown safe and efficient operation, however questions have been raised about possible occurrence of local hot spots in the Pebble Bed which may affect the Pebble integrity. Analysis of the fuel integrity requires detailed evaluation of local heat transport phenomena in a Pebble Bed, and since such phenomena cannot easily be modelled experimentally, numerical simulations are a useful tool. As a part of a European project, named Thermal Hydraulics of Innovative Nuclear Systems (THINS), a benchmarking quasi-direct numerical simulation (q-DNS) of a well-defined Pebble Bed configuration has been performed. This q-DNS will serve as a reference database in order to evaluate the prediction capabilities of different turbulence modelling approaches. A wide range of numerical simulations based on different available turbulence modelling approaches are performed and compared with the reference q-DNS. This paper reports a detailed comparison of LES, Hybrid (RANS/LES) and RANS models with the reference q-DNS. These simulations are performed for a well-defined single face cubic centred Pebble configuration. The obtained flow and thermal fields are extensively analyzed to understand the flow physics in such complex flow regime. Furthermore, lessons learned from these simulations are summarized in the form of guidelines for such complex flow configurations. In addition, following these guidelines, a strategy has been developed to perform large eddy simulations of a realistic limited sized random Pebble Bed.

  • quasi direct numerical simulation of a Pebble Bed configuration part i flow velocity field analysis
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract High temperature reactors (HTR) are being considered for deployment around the world because of their excellent safety features. The fuel is emBedded in a graphite moderator and can sustain very high temperatures. However, the appearance of hot spots in the Pebble Bed cores of HTR's may affect the integrity of the Pebbles. A good prediction of the flow and heat transport in such a Pebble Bed core is a challenge for available turbulence models and such models need to be validated. In the present article, quasi direct numerical simulations (q-DNS) of a Pebble Bed configuration are reported, which may serve as a reference for the validation of different turbulence modeling approaches. Such approaches can be used in order to perform calculations for a randomly arranged Pebble Bed. Simulations are performed at a Reynolds number of 3088, based on Pebble diameter, with a porosity level of 0.42. Detailed flow analyses have shown complex physics flow behavior and make this case challenging for turbulence model validation. Hence, a wide range of qualitative and quantitative data for velocity and temperature field have been extracted for this benchmark. In the present article (part I), results related to the flow field (mean, RMS and covariance of velocity) are documented and discussed in detail. Moreover, the discussion regarding the temperature field will be published in a separate article.

  • quasi direct numerical simulation of a Pebble Bed configuration part ii temperature field analysis
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract Good prediction of the flow and heat transfer phenomena in the Pebble Bed core of a high temperature reactor (HTR) is a challenge for available turbulence models, which still require to be validated. While experimental data are generally desirable in this validation process, due to the complex geometric configuration and measurement difficulties, a very limited amount of data is currently available. On the other hand, direct numerical simulation (DNS) is considered an accurate simulation technique, which may serve as an alternative for validating turbulence models. In the framework of the present study, quasi-direct numerical simulation (q-DNS) of a single face cubic centered Pebble Bed is performed, which will serve as a reference for the validation of different turbulence modeling approaches in order to perform calculations for a randomly arranged Pebble Bed. These simulations were performed at a Reynolds number of 3088, based on Pebble diameter, with a porosity level of 0.42. Results related to flow field (mean, RMS and covariance of velocity) have been presented in Part-I, whereas, in the present article, we focus our attention to the analysis of the temperature field. A wide range of qualitative and quantitative data for the thermal field (mean, RMS and turbulent heat flux) has been generated.

  • numerical simulations of a Pebble Bed configuration using hybrid rans les methods
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract A High Temperature Reactor (HTR) is envisaged to be one of the reactor designs to play a role in nuclear power generation including process heat applications. The HTR design concept exhibits excellent safety features due to the low power density and the large amount of graphite present in the core which gives a large thermal inertia in the event of an accident such as loss of coolant. However, the possible appearance of hot spots in the Pebble Bed cores of HTR may affect the integrity of the Pebbles. This has drawn the attention of several scientists to understand this highly three-dimensional complex phenomenon. To obtain accurate predictions based on techniques such as DNS and LES, for a realistic Pebble Bed flow, is still computationally too expensive and not foreseeable in the near future. On the other hand the prediction capabilities of turbulence modeling approaches such as RANS and hybrid RANS–LES methods for such complex flow regime have not yet been rigorously evaluated. In the present study, numerical simulations of a single cubic Pebble Bed configuration using hybrid RANS–LES methods are presented. Various delayed detached eddy simulation (DDES) methods based on Spalart–Allmaras and k–ω SST models are used for the calculations. Moreover, an extensive qualitative and quantitative comparison has been performed between the obtained results and available quasi-DNS data. Results are found to be in good agreement and support the use of hybrid (RANS/LES) for such type of complex flow configurations.

E.m.j. Komen - One of the best experts on this subject based on the ideXlab platform.

  • improved delayed detached eddy simulation of a randomly stacked nuclear Pebble Bed
    Computers & Fluids, 2015
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract The high temperature reactor (HTR) design concept exhibits excellent safety features due to the low power density and the large amount of graphite present in the core which gives a large thermal inertia in the event of an accident such as loss of coolant. However, the possible appearance of hot spots in a Pebble Bed core design may affect the integrity of the Pebbles and the fuel. This has drawn the attention of several scientists to understand this highly three-dimensional complex phenomenon. To obtain accurate predictions based on techniques such as DNS and LES, for a realistic (even for a small size) Pebble Bed flow, is still computationally too expensive and not foreseeable in the near future. On the other hand, the prediction capabilities of turbulence modelling approaches such as RANS and hybrid RANS-LES methods for such complex flow regime have not yet been rigorously evaluated. In this paper, numerical simulations of a limited sized randomly stacked Bed of spherical Pebbles are performed by using improved delayed detached eddy simulation (IDDES). The Pebble Bed configuration analysed consists of approximately 30 Pebbles, which are randomly stacked to represent the core of an HTR. The obtained results are compared (qualitatively and quantitatively) with the available reference LES for validation purposes. The results show that the selected IDDES based on the SST k-ω model is able to reproduce the overall flow topology. The mean flow and thermal fields are found to be in good agreement with the LES. However, the second order statistics have shown significant disagreement. Nevertheless, these results are explicitly discussed in detail to understand the flow and thermal fields appearing in this complex flow configuration.

  • Numerical simulation of nuclear Pebble Bed configurations
    Nuclear Engineering and Design, 2015
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract High Temperature Reactors (HTRs) are being considered all over the world. An HTR uses helium gas as a coolant, while the moderator function is taken up by graphite. The fuel is emBedded in the graphite moderator. A particular inherent safety advantage of HTR designs is that the graphite can withstand very high temperatures, that the fuel inside will stay inside the graphite Pebble and cannot escape to the surroundings even in the event of loss of cooling. Generally, the core can be designed using a graphite Pebble Bed. Some experimental and demonstration reactors have been operated using a Pebble Bed design. The test reactors have shown safe and efficient operation, however questions have been raised about possible occurrence of local hot spots in the Pebble Bed which may affect the Pebble integrity. Analysis of the fuel integrity requires detailed evaluation of local heat transport phenomena in a Pebble Bed, and since such phenomena cannot easily be modelled experimentally, numerical simulations are a useful tool. As a part of a European project, named Thermal Hydraulics of Innovative Nuclear Systems (THINS), a benchmarking quasi-direct numerical simulation (q-DNS) of a well-defined Pebble Bed configuration has been performed. This q-DNS will serve as a reference database in order to evaluate the prediction capabilities of different turbulence modelling approaches. A wide range of numerical simulations based on different available turbulence modelling approaches are performed and compared with the reference q-DNS. This paper reports a detailed comparison of LES, Hybrid (RANS/LES) and RANS models with the reference q-DNS. These simulations are performed for a well-defined single face cubic centred Pebble configuration. The obtained flow and thermal fields are extensively analyzed to understand the flow physics in such complex flow regime. Furthermore, lessons learned from these simulations are summarized in the form of guidelines for such complex flow configurations. In addition, following these guidelines, a strategy has been developed to perform large eddy simulations of a realistic limited sized random Pebble Bed.

  • quasi direct numerical simulation of a Pebble Bed configuration part i flow velocity field analysis
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract High temperature reactors (HTR) are being considered for deployment around the world because of their excellent safety features. The fuel is emBedded in a graphite moderator and can sustain very high temperatures. However, the appearance of hot spots in the Pebble Bed cores of HTR's may affect the integrity of the Pebbles. A good prediction of the flow and heat transport in such a Pebble Bed core is a challenge for available turbulence models and such models need to be validated. In the present article, quasi direct numerical simulations (q-DNS) of a Pebble Bed configuration are reported, which may serve as a reference for the validation of different turbulence modeling approaches. Such approaches can be used in order to perform calculations for a randomly arranged Pebble Bed. Simulations are performed at a Reynolds number of 3088, based on Pebble diameter, with a porosity level of 0.42. Detailed flow analyses have shown complex physics flow behavior and make this case challenging for turbulence model validation. Hence, a wide range of qualitative and quantitative data for velocity and temperature field have been extracted for this benchmark. In the present article (part I), results related to the flow field (mean, RMS and covariance of velocity) are documented and discussed in detail. Moreover, the discussion regarding the temperature field will be published in a separate article.

  • quasi direct numerical simulation of a Pebble Bed configuration part ii temperature field analysis
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract Good prediction of the flow and heat transfer phenomena in the Pebble Bed core of a high temperature reactor (HTR) is a challenge for available turbulence models, which still require to be validated. While experimental data are generally desirable in this validation process, due to the complex geometric configuration and measurement difficulties, a very limited amount of data is currently available. On the other hand, direct numerical simulation (DNS) is considered an accurate simulation technique, which may serve as an alternative for validating turbulence models. In the framework of the present study, quasi-direct numerical simulation (q-DNS) of a single face cubic centered Pebble Bed is performed, which will serve as a reference for the validation of different turbulence modeling approaches in order to perform calculations for a randomly arranged Pebble Bed. These simulations were performed at a Reynolds number of 3088, based on Pebble diameter, with a porosity level of 0.42. Results related to flow field (mean, RMS and covariance of velocity) have been presented in Part-I, whereas, in the present article, we focus our attention to the analysis of the temperature field. A wide range of qualitative and quantitative data for the thermal field (mean, RMS and turbulent heat flux) has been generated.

  • numerical simulations of a Pebble Bed configuration using hybrid rans les methods
    Nuclear Engineering and Design, 2013
    Co-Authors: Afaque Shams, Ferry Roelofs, E.m.j. Komen, Emilio Baglietto
    Abstract:

    Abstract A High Temperature Reactor (HTR) is envisaged to be one of the reactor designs to play a role in nuclear power generation including process heat applications. The HTR design concept exhibits excellent safety features due to the low power density and the large amount of graphite present in the core which gives a large thermal inertia in the event of an accident such as loss of coolant. However, the possible appearance of hot spots in the Pebble Bed cores of HTR may affect the integrity of the Pebbles. This has drawn the attention of several scientists to understand this highly three-dimensional complex phenomenon. To obtain accurate predictions based on techniques such as DNS and LES, for a realistic Pebble Bed flow, is still computationally too expensive and not foreseeable in the near future. On the other hand the prediction capabilities of turbulence modeling approaches such as RANS and hybrid RANS–LES methods for such complex flow regime have not yet been rigorously evaluated. In the present study, numerical simulations of a single cubic Pebble Bed configuration using hybrid RANS–LES methods are presented. Various delayed detached eddy simulation (DDES) methods based on Spalart–Allmaras and k–ω SST models are used for the calculations. Moreover, an extensive qualitative and quantitative comparison has been performed between the obtained results and available quasi-DNS data. Results are found to be in good agreement and support the use of hybrid (RANS/LES) for such type of complex flow configurations.

Mikio Enoeda - One of the best experts on this subject based on the ideXlab platform.

  • LAYERED Pebble Bed CONCEPT FOR ITER BREEDING BLANKET
    Fusion Technology 1992, 2013
    Co-Authors: Hideyuki Takatsu, Mikio Enoeda, S. Mori, H. Yoshida, T. Hashimoto, T. Kurasawa, Kouichi Koizumi, S. Satoh, T. Kuroda, T. Suzuki
    Abstract:

    Design efforts have been continued to refine and simplify the layered Pebble Bed design for the ITER breeding blanket. Detailed neutronics and thermal analyses were conducted to investigate the optimal configuration. Static and dynamic stress analyses were carried out to examine stress and deformation of the blanket box structure under disruption electromagnetic forces. Fabrication and assembly procedure were also studied. The present paper summarizes current status of the layered Pebble Bed breeding blanket design.

  • status of ceramic breeder Pebble Bed thermo mechanics r d and impact on breeder material mechanical strength
    Fusion Engineering and Design, 2012
    Co-Authors: Alice Ying, Mikio Enoeda, J. Reimann, Lorenzo Boccaccini, Marc Kamlah, R Knitter, Yixiang Gan, Jaap G Van Der Laan, L Magielsen, P A Di Maio
    Abstract:

    Abstract Among the international fusion solid breeder blanket community, there exists steady progress on the experimental, phenomenological, and numerical characterizations of the Pebble Bed effective thermo physical and mechanical properties, and of thermomechanic state of the Bed under prototypical operating conditions. This paper summarizes recent achievements in Pebble Bed thermomechanics that were carried out by members of the IEA Fusion Nuclear Technology Subtask I Solid Breeding Blanket. A major goal is on developing predictive capability while identifying a pre-conditioned equilibrium stress state that would warrant Pebble Bed integrity during operations. The paper reviews and synthesizes existing computational modeling approaches for Pebble Bed thermomechanics prediction, and differentiating points of convergence/divergence among existing approaches. The progress toward modeling benchmark is also discussed. These advancements have led to a framework to help navigate future research.

  • Packing behaviour of a Li2TiO3 Pebble Bed under cyclic loads
    Journal of Nuclear Materials, 2011
    Co-Authors: Hisashi Tanigawa, Yuichiro Tanaka, Mikio Enoeda
    Abstract:

    Abstract In the temperature range from room temperature to 973 K and the mechanical loading range from 0.1 to 3 MPa, a Li 2 TiO 3 Pebble Bed was successively loaded and the packing behaviour of the Bed was observed. Deformation caused by the mechanical loading is partly relaxed when the Bed is heated without the load. After a large numbers of thermal and mechanical loading cycles, the packing factor of the Bed increased from the initial packing factor of 66.9% to finally about 68.5%. This progressive increase in packing leads to production of a cavity region at the top of the Pebble Bed, therefore it is important to obtain a high initial packing factor.

  • R&D of a Li2TiO3 Pebble Bed for a test blanket module in JAEA
    Nuclear Fusion, 2009
    Co-Authors: Hiroyasu Tanigawa, Mikio Enoeda, Tsuyoshi Hoshino, Yoshinori Kawamura, Masaru Nakamichi, Kentaro Ochiai, Masato Akiba, M. Ando, Koichiro Ezato, K. Hayashi
    Abstract:

    At JAEA, a test blanket module (TBM) with a water-cooled solid breeder is being developed. This paper presents recent achievements of research activities for the TBM, particularly addressing the Pebble Bed of the tritium breeder materials and tritium behaviour. For the breeder material, the chemical stability of Li2TiO3 was improved using Li2O additives. To analyse the Pebble Bed behaviour, thermomechanical properties of the Li2TiO3 Pebble Bed were assessed experimentally. To verify the Pebble Bed's nuclear properties, the activation foil method was proposed and a preliminary experiment was conducted. To reduce the tritium permeation, the chemical densified coating method was developed and the coating was attached to F82H steel. For tritium behaviour, the tritium recovery system was modified in consideration of the design change of the TBM.

  • Pressurizing behavior on ingress of coolant into Pebble Bed of blanket of Fusion DEMO reactor
    2007
    Co-Authors: Daigo Tsuru, Mikio Enoeda, Masato Akiba
    Abstract:

    In the safety design and technology of blankets for the Fusion DEMO reactor developed in Japan, coolant ingress in the blanket box structure is one of the most important events. Especially, the thermal hydraulics in the Pebble Bed in the case of the high-pressure coolant ingress is very important to evaluate the pressure propagation and coolant flow behavior. This paper presents the preliminary results of the pressure loss characteristics by the coolant ingress in the Pebble Bed. Experiments have been performed to simulate the helium coolant ingress into breeder and multiplier Pebble Beds and to evaluate the pressure loss in the Pebble Beds. The measured pressure loss is compared with the predicted values by Ergun's equation, which is the correlation equation on pressure loss of the flow through porous medium. Parameter study is carried out and dependencies of pressure loss through Pebble Bed on pressure and packing factor is evaluated. Method to reduce the maximum pressure in solid breeder blanket after pipe rupture accident is discussed. Enhancement of pressure loss in upstream and reduction of pressure loss in downstream is effective.