kth.sePublications
Change search
Refine search result
1 - 15 of 15
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Dokhane, A.
    et al.
    Judd, J.
    Gajev, Ivan
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Zerkak, O.
    Ferroukhi, H.
    Kozlowski, T.
    Analysis of Oskarshamn-2 stability event using TRACE/SIMULATE-3K and comparison to TRACE/PARCS and SIMULATE-3K stand-alone2017In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 102, p. 190-199Article in journal (Refereed)
    Abstract [en]

    With the goal to enhance the capability to perform best-estimate simulations of Light Water Reactors (LWRs) transients, with strong coupling between core neutronics and plant thermal-hydraulic, a coupling between TRACE and SIMULATE-3K (TS3K) was developed in collaboration between PSI and Studsvik for analyses involving interactions between system and core. In order to verify the coupling scheme and the coupled code capabilities to simulate complex transients, the OECD/NEA Oskarshmn-2 (O-2) Stability benchmark was modeled with the coupled code TS3K. The main goal of this paper is to present TS3K analyses of the Oskarshamn-2 stability event, noting that this constitutes the first reported assessment of this code system for a BWR stability problem. A systematic analysis is carried out using different time-space discretization schemes in order to identify an optimized methodology to simulate correctly the O-2 stability event. In this context, the TS3K results are compared to the available benchmark data both for steady-state and transient conditions. The results show that using a refined model in space and time, the TS3K model can successfully capture the entire behavior of the transient qualitatively, i.e. onset of the instability with growing oscillation amplitudes, as well as quantitatively, i.e. Decay Ratio and resonance frequency. In addition, the results are compared also to those obtained using TRACE/PARCS and S3K stand-alone, which allows a systematic comparison between different codes.

  • 2.
    Gajev, Ivan
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Sensitivity and Uncertainty Analysis of Boiling Water Reactor Stability Simulations2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The best estimate codes are used for licensing of Nuclear Power Plants (NPP), but with conservative assumptions. It is claimed that the uncertainties are covered by the conservatism of the calculation. Nowadays, it is possible to estimate certain parameters using non-conservative data with the complement of uncertainty evaluation, and these calculations can also be used for licensing. As NPPs are applying for power up-rates and life extension, new licensing calculations need to be performed. In this case, evaluation of the uncertainties could help improve the performance, while staying below the limit of the safety margins.

    Given the problem of unstable behavior of Boiling Water Reactors (BWR), which is known to occur at certain power and flow conditions, it could cause SCRAM and decrease the economic performance of the plant. Performing an uncertainty analysis for BWR stability would give better understating of the phenomenon and it would help to verify and validate (V&V) the codes used to predict the NPP behavior.

    This thesis, reports a sensitivity/uncertainty study of numerical, neutronics, and thermal-hydraulics parameters on the prediction of the BWR stability within the framework of OECD Ringhals-1 (R1 stable reactor) and OECD Oskarshamn-2 (O2 unstable reactor) stability benchmarks. The time domain code TRACE/PARCS was used in the analyses. This thesis is divided in three parts: space-time convergence; uncertainty; sensitivity.

    A space-time convergence study was done for the numerical parameters (nodalization and time step). This was done by refining nodalization of all components and time step until obtaining space-time converged solution, i.e. further refinement doesn’t change the solution. When the space-time converged solutions were compared to the initial models, much better solution accuracy has been obtained for the stability measures (decay ratio and frequency), for both stable (R1) and unstable (O2) reactors with the space-time converged models.

    Further on, important neutronics and thermal-hydraulics parameters were identified and an uncertainty calculation was performed using the Propagation of Input Errors (PIE) methodology. This methodology, also known as the GRS method, has been used because it has been extensively tested and verified by the industry, and because it allows identifying the most influential parameters using the spearman rank correlation method.

    Using the uncertainty method’s results, an attempt has been done to identify the most influential parameters affecting the stability. A methodology using the spearman rank correlation coefficient has been implemented, which helps to identify the most influential parameters on the stability (decay ratio and frequency). Additional sensitivity calculations have been performed for better understanding of BWR stability and parameters that affect it.

    Download full text (pdf)
    PhD_Thesis_Ivan_Gajev
  • 3.
    Gajev, Ivan
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Sensitivity and Uncertainty Analysis of BWR Stability2010Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Best Estimate codes are used for licensing, but with conservative assumptions. It is claimed that the uncertainties are covered by the conservatism of the calculation. As Nuclear Power Plants are applying for power up-rates and life extension, evaluation of the uncertainties could help improve the performance, while staying below the limit of the safety margins.

     

    Given the problem of unstable behavior of Boiling Water Reactors (BWRs), which is known to occur during operation at certain power and flow conditions, it could cause SCRAM and decrease the economic performance of the plant. Performing an uncertainty analysis for BWR stability would give better understating of the phenomenon and it would help to verify and validate (V&V) the codes used to predict the NPP behavior.

     

    This thesis reports an uncertainty study of the impact of Thermal-Hydraulic, Neutronic, and Numerical parameters on the prediction of the stability of the BWR within the framework of OECD Ringhals-1 stability benchmark. The time domain code TRACE/PARCS was used in the analysis. This thesis is divided in two parts: Sensitivity study on Numerical Discretization Parameters (Nodalization, Time Step, etc.) and Uncertainty part.

     

    A Sensitivity study was done for the Numerical Parameters (Nodalization and Time step). This was done by refining all possible components until obtaining Space-Time Converged Solution, i.e. further refinement doesn’t change the solution. When the space-time converged solution was compared to the initial discretization, a much better solution has been obtained for both the stability measures (Decay Ratio and Frequency) with the space-time converged model.

     

    Further on, important Neutronic and Thermal-Hydraulic Parameters were identified and the uncertainty calculation was performed using the Propagation of Input Errors (PIE) methodology. This methodology, also known as the GRS method, has been used because it has been tested and extensively verified by the industry, and because it allows identifying the most influential parameters using the Spearman Rank Correlation.

    Download full text (pdf)
    FULLTEXT01
  • 4.
    Gajev, Ivan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Kozlowski, T.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Space-time convergence study based on OECD Ringhals-1 Stability Benchmark2012In: Transactions of the American Nuclear Society: Volume 106, 2012, 2012, p. 984-987Conference paper (Refereed)
  • 5.
    Gajev, Ivan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Kozlowski, Tomasz
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Xu, Yunlin
    Downar, Thomas
    Ranking of Input Parameters Importance for BWR Stability Based on Ringhals-12011In: International Conference on Mathematics and Computational Methods applied to Nuclear Science and Engineering (MC 2011), 2011Conference paper (Refereed)
  • 6.
    Gajev, Ivan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Kozlowski, Tomasz
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Xu, Yunlin
    Downar, Thomas
    Sensitivity and Uncertainty of BWR Ringhals-1 TRACE/PARCS Stability Prediction2009In: 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 2009Conference paper (Refereed)
  • 7.
    Gajev, Ivan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Kozlowski, Tomasz
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Xu, Yunlin
    Downar, Thomas
    Sensitivity and Uncertainty of OECD Benchmark Ringhals-1TRACE/PARCS Stability Prediction2012In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 180, no 3, p. 383-398Article in journal (Refereed)
    Abstract [en]

    Unstable behavior of boiling water reactors (BWRs) is known to occur during operation at certain power and flow conditions. This paper reports on an uncertainty study of the impact of various parameters on the prediction of the stability of the BWR within the framework of the Organisation for Economic Co-operation and Development Ringhals Unit 1 (Ringhals-1) Stability Benchmark. The time domain code TRACE/PARCS was used in the analysis. The paper is divided into two parts: a sensitivity study on numerical parameters (nodalization, time step, etc.) and an uncertainty analysis of the stability event. The sensitivity study was based on a space-time converged solution, and the most important neutronic and thermal-hydraulic parameters were identified for parameterization. The uncertainty calculation was then performed using the well-established propagation of input errors methodology. Finally, the Spearman Rank method was used to identify the most influential parameters affecting the stability of Ringhals-1.

  • 8.
    Gajev, Ivan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Kozlowski, Tomasz
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Xu, Yunlin
    Downar, Thomas
    Sensitivity and Uncertainty of the Neutronic Parameters of BWR Ringhals-1 TRACE/PARCS Stability Prediction2010In: International Conference on the Physics of Reactors 2010, PHYSOR 2010, 2010, p. 3320-3331Conference paper (Refereed)
    Abstract [en]

    Unstable behavior of Boiling Water Reactors (BWRs) is known to occur during operation at certain power and flow conditions. This paper reports the results of a preliminary investigation of the impact of uncertainty neutronic parameters on the prediction of the stability of the BWR within the framework of OECD Ringhals-1 stability benchmark. The time domain code TRACE/PARCS was used in the analysis and sensitivity calculations were performed for every neutronic parameter which was anticipated to affect the stability prediction of the reactor. The overall objective of the work here was to identify parameters most significantly affecting the stability phenomena in the Ringhals-1 stability benchmark. Using selected parameters, an uncertainty method based on the propagation of code input errors was used to obtain tolerance limits for the decay ratio and the frequency prediction. The scope of the uncertainty study reported in this paper was limited to the neutronic effects. Further studies will include other effects to include thermal-hydraulic parameters and modeling effects.

  • 9.
    Gajev, Ivan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Kozlowski, Tomasz
    University of Illinois, United States .
    Sensitivity analysis of input uncertain parameters on BWR stability using TRACE/PARCS2014In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 67, p. 49-58Article in journal (Refereed)
    Abstract [en]

    The unstable behavior of Boiling Water Reactors (BWR), which is known to occur at certain power and flow conditions, could cause SCRAM and decrease the economic performance of the plant. For better prediction of BWR stability and understanding of influential parameters, two TRACE/PARCS models of Ringh-als-1 and Oskarshamn-2 BWRs were employed to perform a sensitivity study. Using the propagation of input errors uncertainty method's results, an attempt has been made to identify the most influential parameters affecting the stability. Furthermore, a methodology using the spearman rank correlation coefficient has been used to identify the most influential parameters on the stability parameters (decay ratio and frequency).

  • 10.
    Gajev, Ivan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Kozlowski, Tomasz
    Univ Illinois, USA.
    Space–time convergence analysis on BWR stability using TRACE/PARCS2013In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 51, p. 295-306Article in journal (Refereed)
    Abstract [en]

    Unstable behavior of Boiling Water Reactors (BWRs) is known to occur during operation at certain power and flow conditions. Even though BWR instability is not a severe safety concern, it could cause reactor scram and significantly decrease the economic performance of the plant. This paper aims to (a) quantify TRACE/PARCS space–time discretization error for simulation of BWR stability, (b) establish space (nodalization) and time discretization necessary for space–time converged model and (c) show that the space–time converged model gives more reliable results for both stable and unstable reactor. The space–time converged model is obtained when further refinement of numerical discretization parameters (nodalization and time step) has negligible effect on the solution. The study is significant because performing a space–time convergence analysis is a necessary step of qualification of the TRACE/PARCS model, and use of the space–time converged model increases confidence in the prediction of BWR stability.

  • 11.
    Gajev, Ivan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Kozlowski, Tomasz
    Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, United States.
    Uncertainty analysis of the OECD/NRC Oskarshamn-2 BWR stability Benchmark2014In: Proceedings of the International Conference on Physics of Reactors, PHYSOR 2014, Japan Atomic Energy Agency, JAEA , 2014Conference paper (Refereed)
    Abstract [en]

    On February 25, 1999, the Oskarshamn-2 NPP experienced a stability event which culminated in diverging power oscillations with a decay ratio of about 1.4. The event was successfully modeled by the TRACE/PARCS coupled system code, and further uncertainty analysis of the event is described in this paper. The results show very good agreement with the plant data, capturing the entire behavior of the transient including the onset of instability, growth of the oscillations (decay ratio) and oscillation frequency. This provides confidence in the prediction of other parameters which are not available from the plant records. This paper shows also how an uncertainty method was implemented for the event. Comparing the calculated uncertainty with the measured uncertainty gives confidence in the BWR stability prediction.

  • 12.
    Kozlowski, Tomasz
    et al.
    University of Illinois, Urbana, IL, United States.
    Peltonen, Joanna
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Gajev, Ivan
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Phung, Viet-Anh
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Roshan, Sean
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Predicting actual reactor conditions: Why timedomain simulation is necessary for BWR stability2013In: International Journal of Nuclear Energy Science and Technology, ISSN 1741-6361, Vol. 7, no 4, p. 319-342Article in journal (Refereed)
    Abstract [en]

    Despite two decades of development and successful use of coupled thermal-hydraulics/neutron-kinetics (TH/NK) codes for the analysis of design basis accidents, the application of coupled codes to BWR stability transients remains a formidable challenge. While the issues in physical models and numerical methods can be identified, quantified and managed through special developments and separate-effect tests, other aspects (e.g. coupling, modelling assumptions) can only be addressed through benchmarking on full plant stability tests. However, often incomplete information causes uncertainties, whose significance on the modelling and simulation must be evaluated. The objective of this paper is to define validation data needs that allow prediction of the transient behaviour should an unstable condition occur. It is shown that the confidence in exploiting advantageous features of the coupled TH/NK system codes in dealing with core-plant interaction, transient effects and local perturbations can only be evaluated with well-characterised, well-documented plant stability tests and stability events.

  • 13. Kozlowski, Tomasz
    et al.
    Wysocki, Aaron
    Gajev, Ivan
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Xu, Yunlin
    Downar, Thomas
    Ivanov, Kostadin
    Magedanz, Jeffrey
    Hardgrove, Matthew
    March-Leuba, Jose
    Hudson, Nathanael
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Analysis of the OECD/NRC Oskarshamn-2 BWR stability benchmark2014In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 67, p. 4-12Article in journal (Refereed)
    Abstract [en]

    On February 25, 1999, the Oskarshamn-2 NPP experienced a stability event which culminated in diverging power oscillations. The event was successfully modeled by the TRACE/PARCS coupled system code, and further uncertainty analysis of the event is described in this paper. The results show very good agreement with the plant data, capturing the entire behavior of the transient including the onset of instability, growth of the oscillations, and oscillation frequency. This provides confidence in the prediction of other parameters which are not available from the plant records. The event provides coupled code validation for a challenging BWR stability event, which involves the accurate simulation of neutron kinetics (NK), thermal-hydraulics (TH), and TH/NK coupling. The success of this work has demonstrated the ability of the 3-D coupled systems code TRACE/PARCS to capture the complex behavior of BWR stability events. The problem was released as an international OECD/NEA benchmark, and it is the first benchmark based on measured plant data for a stability event with a DR greater than one.

  • 14.
    Zerkak, Omar
    et al.
    Paul Scherrer Institut.
    Gajev, Ivan
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Manera, Annalisa
    Paul Scherrer Institut.
    Kozlowski, Tomasz
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Gommlich, Andre
    Helmholtz-Zentrum Dresden-Rossendorf.
    Zimmer, Stéphanie
    Commissariat à l’Energie Atomique.
    Kliem, Sören
    Helmholtz-Zentrum Dresden-Rossendorf.
    Crouzet, Nicolas
    Commissariat à l’Energie Atomique.
    Zimmermann, Martin A.
    Paul Scherrer Institut.
    Revisiting Temporal Accuracy in Neutronics/THCode Coupling Using the NURESIM LWRSimulation Platform2011In: The 14th Internation Topical Meetingon Nuclear Reactor Thermalhydraulics (NURETH-14), 2011Conference paper (Refereed)
    Abstract [en]

    The first part of this paper reviews the different temporal coupling methodologies that are currentlyemployed for the transient simulation of LWR cores. The second part shows preliminary resultsfrom the implementation of some suggested coupling improvements, including high-ordercorrections to the exchanged coupling fields and a dynamic time step control technique, for thesimulation of an exemplary reactivity insertion transient analysed using the European NURESIMLWR simulation platform.

  • 15. Zerkak, Omar
    et al.
    Kozlowski, Tomasz
    Gajev, Ivan
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Review of multi-physics temporal coupling methods for analysis of nuclear reactors2015In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 84, p. 225-233Article in journal (Refereed)
    Abstract [en]

    The advanced numerical simulation of a realistic physical system typically involves multi-physics problem. For example, analysis of a LWR core involves the intricate simulation of neutron production and transport, heat transfer throughout the structures of the system and the flowing, possibly two-phase, coolant. Such analysis involves the dynamic coupling of multiple simulation codes, each one devoted to the solving of one of the coupled physics. Multiple temporal coupling methods exist, yet the accuracy of such coupling is generally driven by the least accurate numerical scheme. The goal of this paper is to review in detail the approaches and numerical methods that can be used for the multi-physics temporal coupling, including a comprehensive discussion of the issues associated with the temporal coupling, and define approaches that can be used to perform multi-physics analysis. The paper is not limited to any particular multi-physics process or situation, but is intended to provide a generic description of multi-physics temporal coupling schemes for any development stage of the individual (single-physics) tools and methods. This includes a wide spectrum of situation, where the individual (single-physics) solvers are based on pre-existing computation codes embedded as individual components, or a new development where the temporal coupling can be developed and implemented as a part of code development. The discussed coupling methods are demonstrated in the framework of LWR core analysis.

1 - 15 of 15
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf