| 1. |
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| 2. |
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| 3. |
- Cadinu, Francesco, et al.
(författare)
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Relating system-to-CFD coupled code analyses to theoretical framework of a multiscale method
- 2008
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Ingår i: Societe Francaise d'Energie Nucleaire - International Congress on Advances in Nuclear Power Plants - ICAPP 2007, "The Nuclear Renaissance at Work". - 9781604238716 ; , s. 2959-2967
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Konferensbidrag (refereegranskat)abstract
- Over past decades, analyses of transient processes and accidents in a nuclear power plan t have been performed, to a significant extent and with an admirable success, by means of so called system codes, e.g. RELAP5, CATHARE, ATHLET codes. These computer codes, based on a multi-fluid model of two-phase flow, provide an effective, one-dimensional description of the coolant thermal-hydraulics in the reactor system. For some components in the system, wherever needed, the effect of multi-dimensional flow is accounted for through approximate models. The later are derived from scaled experiments conducted for selected accident scenarios. Increasingly, however, we have to deal with newer and ever more complex accident scenarios. In some such cases the system codes fail to serve as simulation vehicle, largely due to its deficient treatment of multi-dimensional flow (in e.g. downcomer, lower plenum). Enter Computational Fluid Dynamics (CFD). Based on solving Navier-Stokes equations, CFD codes have been developed and used, broadly, to perform analysis of multi-dimensional flow, dominantly in non-nuclear industry and for single-phase flow applications. Although not always straightforward, CFD codes can be, and have been, used to analyze thermo-fluid processes in a certain component of the reactor system at a well-defined point during the accident progression. It is natural to think that CFD codes provide the much-needed complementary capability to the system codes. Furthermore, due to the CFD excessive demand on computational resources, ideas were proposed, and attempts were reported in the literature, to use a coupled system-to-CFD code to maximize the benefit of both tools. Easy as it might sound, progress in this area has been sluggish. In this paper, we take a close look at the progress in coupled system-to-CFD code analyses, including coupling algorithms, their implementation and performance. Tackling thermo-fluid dynamics at largely different scales, system codes and CFD codes employ different models and governing equations. This notion led us to the idea to examine the system-to-CFD coupling in the language of multiscale simulations. As a theoretical framework, we bring to bear the heterogeneous multiscale method pioneered by E and Engquist and problem classification offered by E et al.[16]. Viewing system-to-CFD coupling as a multiscale problem, the ultimate objective of the present effort is to define requirements for models and numerical methods, and develop suggestions on a coupling strategy that ensures robust and effective generation and transfer of information between scale-specific simulations (system and CFD).
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| 4. |
- Cadinu, Francesco, et al.
(författare)
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Study of algorithmic requirements for a system-to-CFD coupling strategy
- 2008
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Ingår i: Experiments and CFD Code Application to Nuclear Reactor Safety (XCFD4NRS).
-
Konferensbidrag (refereegranskat)abstract
- Over the last decades, the analysis of transients and accidents in nuclear power plants has beenperformed by system codes. Though they will remain the analyst’s tool of choice for the foreseeablefuture, their limitations are also well known. It has been suggested that an improvement in thesimulation technology can be obtained by “coupling” system codes with Computational FluidDynamics (CFD) calculations. This is usually attempted in a domain decomposition fashion: the CFDsimulation is only performed in a selected subdomain and its solution is “matched” with the systemcode solution at the interface. However, another coupling strategy can be envisioned. Namely, CFDsimulations can be used to provide closures to a system code.This strategy is based on the following two assumptions. The first assumption is that there aretransients which cannot be simulated by system codes because of the lack of adequate closures. Thesecond assumption is that appropriate closures can be provided by CFD simulations. In this paper,such a coupling strategy, inspired by the Heterogeneous Multiscale Method (HMM), is presented. Thephilosophy underlying this strategy is discussed with the help of a computational example.
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| 5. |
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| 6. |
- Gajev, Ivan, et al.
(författare)
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Sensitivity analysis of input uncertain parameters on BWR stability using TRACE/PARCS
- 2014
-
Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 67, s. 49-58
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Tidskriftsartikel (refereegranskat)abstract
- 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).
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| 7. |
- Gajev, Ivan, 1985-
(författare)
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Sensitivity and Uncertainty Analysis of Boiling Water Reactor Stability Simulations
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 8. |
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| 9. |
- Gajev, Ivan, et al.
(författare)
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Sensitivity and Uncertainty of OECD Benchmark Ringhals-1TRACE/PARCS Stability Prediction
- 2012
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 180:3, s. 383-398
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Gajev, Ivan, et al.
(författare)
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Sensitivity and Uncertainty of the Neutronic Parameters of BWR Ringhals-1 TRACE/PARCS Stability Prediction
- 2010
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Ingår i: International Conference on the Physics of Reactors 2010, PHYSOR 2010. ; , s. 3320-3331
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 11. |
- Gajev, Ivan, et al.
(författare)
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Space–time convergence analysis on BWR stability using TRACE/PARCS
- 2013
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 51, s. 295-306
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 12. |
- Gajev, Ivan, et al.
(författare)
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Uncertainty analysis of the OECD/NRC Oskarshamn-2 BWR stability Benchmark
- 2014
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Ingår i: Proceedings of the International Conference on Physics of Reactors, PHYSOR 2014. - : Japan Atomic Energy Agency, JAEA.
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 13. |
- Jaromin, Maria, et al.
(författare)
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Sensitivity Analysis of CFD Two-Phase Flow in a BWR Fuel Bundle
- 2010
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Konferensbidrag (refereegranskat)abstract
- The goal of this work was to perform an investigation of the sensitivities of the average outlet void fraction and flow pattern prediction in the fuel assembly on important model parameters. The model sensitivities were examined on the following groups of parameters: numerical parameters (e.g. mesh discretization), operating conditions (input power, outlet pressure, mass flow rate and inlet temperature) and closure models for the interphase momentum (e.g. drag, virtual mass, lift, turbulent dispersion, wall lubrication). The average outlet void fraction was evaluated by the CFD code for the steady-state and model sensitivities were identified. A significant sensitivity was recognized especially for changes of inlet temperature of coolant and system pressure. Moreover, the turbulent dispersion force and the wall lubrication force had a significant influence on vapor and liquid velocity profiles and also on the distribution of void at the outlet of the fuel assembly.
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| 14. |
- Jönsson, Mikael, et al.
(författare)
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Differences in lens optical plasticity in two gadoid fishes meeting in the Arctic.
- 2014
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Ingår i: Journal of Comparative Physiology A. - : Springer Science and Business Media LLC. - 1432-1351 .- 0340-7594. ; 200:11, s. 949-957
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Tidskriftsartikel (refereegranskat)abstract
- Arctic and boreal/temperate species are likely to be evolutionary adapted to different light regimes. Currently, the boreal/temperate Atlantic cod (Gadus morhua) is coexisting with the native polar cod (Boreogadus saida) in the Arctic waters around Svalbard, Norway. Here, we studied light/dark adaptative optical plasticity of their eye lenses by exposing fish to bright light during the polar night. Schlieren photography, high-definition laser scanning and ray tracing were used to determine the optical properties of excised crystalline lenses. Both species have multifocal lenses, an optical adaptation for improved color vision. In polar cod, the optical properties of the lens were independent of light exposure. In the more southern Atlantic cod, the optical properties of the lens changed within hours upon exposure to light, even after months of darkness. Such fast optical adjustment has previously only been shown in a tropical cichlid. During the polar night the Atlantic cod lens seems to be unregulated and dysfunctional since it had an unsuitable focal length and severe spherical aberration. We present a system, to our knowledge unique, for studying visual plasticity on different timescales in relation to evolutionary history and present the first study on the polar cod visual system.
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| 15. |
- Kozlowski, Tomasz, et al.
(författare)
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Analysis of the OECD/NRC Oskarshamn-2 BWR stability benchmark
- 2014
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 67, s. 4-12
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 16. |
- Kozlowski, Tomasz, et al.
(författare)
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Cell Homogenization Method for Pin-by-Pin Neutron Transport Calculations
- 2011
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Ingår i: Nuclear science and engineering. - 0029-5639 .- 1943-748X. ; 169:1, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- For practical reactor core applications, low-order transport approximations such as SP(3) have been shown to provide sufficient accuracy for both static and transient calculations with considerably less computational expense than the discrete ordinate or the full spherical harmonics methods. These methods have been applied in several core simulators where homogenization was performed at the level of the pin cell. One of the principal problems has been to recover the error introduced by pin cell homogenization. One of the basic approaches to treat pin cell homogenization error is pin cell discontinuity factors (CDFs) based on well-established generalized equivalence theory to generate appropriate group constants. The method is able to treat all sources of error together, allowing even a few-group diffusion solution with one mesh per cell to reproduce a higher-order reference solution. However, a CDF has to be derived separately for each space-angle approximation. An additional difficulty is that in practice the CDFs have to be derived from a lattice calculation from which only the scalar flux and current are available, and therefore recovery of the exact SP(N) angular moment is not possible. This paper focuses on the pin cell scale homogenization. It demonstrates derivation of the CDF for the SP(3) transport method with finite-difference spatial discretization with the limitation of only the scalar flux and interface current being available from the heterogeneous reference. The method is demonstrated using a sample benchmark application.
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| 17. |
- Kozlowski, Tomasz, et al.
(författare)
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Consistent comparison of the codes RELAP5/PARCS and TRAC-M/PARCS for the OECD MSLB coupled code benchmark
- 2004
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 146:1, s. 15-28
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Tidskriftsartikel (refereegranskat)abstract
- A generalized interface module was developed for coupling any thermal-hydraulic code to any spatial kinetic code. In the design used here the thermal-hydraulic and spatial kinetic codes function as independent processes and communicate using the Parallel Virtual Machine software. This approach helps maximize flexibility while minimizing modifications to the respective codes. Using this interface, the U.S. Nuclear Regulatory Commission (NRC) three-dimensional neutron kinetic code, Purdue Advanced Reactor Core Simulator (PARCS), has been coupled to the NRC system analysis codes RELAP5 and Modernized Transient Reactor Analysis Code (TRAC-M). Consistent comparison of code results for the Organization for Economic Cooperation and Development/Nuclear Energy Agency main steam line break benchmark problem using RELAP5/PARCS and TRAC-M/PARCS was made to assess code performance.
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| 18. |
- Kozlowski, Tomasz, et al.
(författare)
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Deterministic Safety Analysis Group. Review for the period of 2008 – 2010
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- SSM has signed an agreement with KTH and Chalmers for a long-term commitment within the deterministic safety analysis (transient and severe accident analysis). The objective for this co-operation is to promote the national competence and to establish groups, whom can support SSM to perform safety analysis, reviews and inquiries, as well as participate in international projects and working groups within these areas. According to the agreement, the analysis groups at KTH and Chalmers have worked with R&D within the following areas: - plant analysis; - evaluation and contribution to international projects; - training and education of SSM's personnel. The first phase of the Technical Support Organization for the Deterministic Safety Analysis (TSO-DSA) agreement covered the period of 2008 ¡V 2010. The objective of this document is to describe the work performed within the TSO-DSA and summarize the TSO-DSA achievements for the initial 3-year period.
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| 19. |
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| 20. |
- Kozlowski, Tomasz, et al.
(författare)
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Evaluation of coupled codes RELAP5/PARCS capability for BWR global stability prediction
- 2007
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Ingår i: Proceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12. - 9780894480584 - 0894480588 ; , s. 1619-1640
-
Konferensbidrag (refereegranskat)abstract
- The present study is concerned with capability of a coupled neutron-kinetic/thermal-hydraulic code system RELAP5/PARCS for the numerical prediction of global core stability condition and instability transients. The work is motivated by the need to assess safety significance of a number of stability transients which trigger core instability and challenge reactor protection systems. The technical approach adopted is both to learn from real stability events and to perform analysis of idealized well-defined transients in a real plant and core configuration. In this paper, we show that the code system can serve as a unique and powerful tool to provide a consistent and reasonably reliable prediction of stability boundary even in complex plant transients. However, the prediction quality of the instability transients, i.e. core behavior without scram, namely parameters of the limit cycle remains questionable. We identify two main factors for future studies (two-phase flow regimes in oscillatory flow and algorithm for effective grouping of thermal-hydraulic channels) as key to enhancing the predictive capability of the existing coupled code system for BWR stability.
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| 21. |
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| 22. |
- Kozłowski, Tomasz M., et al.
(författare)
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Constant lens fiber cell thickness in fish suggests crystallin transport to denucleated cells
- 2019
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Ingår i: Vision Research. - : Elsevier BV. - 0042-6989. ; 162, s. 29-34
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Tidskriftsartikel (refereegranskat)abstract
- The crystalline lens of the vertebrate eye grows throughout life. This growth may be enormous in fish, while the lens must be functional from larva to adult. During growth, the fiber cells of the lens must increase the concentration of specific proteins (crystallins) in the cytoplasm to increase refractive index. However, the bulk of the fiber cells in a vertebrate lens are denucleated and have no organelles to synthesize proteins. To study how this problem is solved, we first measured lens fiber cell thickness in the Nile tilapia, a teleost fish. In the lenses from 25 fish, in two size groups, fibers were considerably thinner than in other vertebrates. Fiber thickness was about constant along the radius of the lens and the same between the size groups. Since our results provided no evidence for shrinkage of lens fiber cells with growth (expected if protein concentration is increased by expelling water) we included eight additional teleost species to elucidate the mechanism by which the cells increase crystallin concentration. In all species, fiber cell thickness was about constant throughout the lens, with species-specific values. The changes in fiber cell thickness expected from an increase in crystallin concentration by removal of water were modeled. Shrinkage in cell thickness by up to 66% would have been necessary to reach the required crystallin concentration. We conclude that crystallin concentration in denucleated lens fiber cells is increased by transport of proteins from synthetically competent cells in the periphery of the lens.
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| 23. |
- Kozłowski, Tomasz M
(författare)
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Fish Lenses : Anatomy and Optics
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- I have investigated some of the biological regulatory mechanisms governing the development of crystalline lenses. I used fish as model animals because they possess optically interesting lenses, while the geometrical simplicity of fish lenses allows for studies that are difficult or impossible with the lenses of other animals.First we have investigated lens optical plasticity by measuring longitudinal spherical aberration in light and dark adapted fish of two species, Atlantic and Polar cod. We noticed that Atlantic cod, native to regions with daily light/dark changes responded to light/dark adaptation by changing the optics of its lens, whereas the optics of Polar cod, living in the polar region, was unchanged on a daily basis (Paper I). However, we observed that the optics of the Polar cod lens changed annually between seasons corresponding to polar day and night (unpublished data). Our findings can be explained by the existence of two different mechanisms controlling the optics of fish lenses. A short-term one adapting the lenses to daily light/dark cycles (Atlantic cod) and a long-term one evolved for coping with long polar days and nights (Polar cod).The second project involved investigation of the osmolality of fish larvae body fluids. We tested two levels of osmolality in two different ways. The first one involved measuring the rate of optical deterioration of excised fish lenses placed in different immersion media, the second one the quality of a whole eye fixation. In both cases, lower osmolality gave better results for fish larvae. The optical quality of larval lenses deteriorated slower and fixation preserved the larval eye in a more natural shape (Paper II). We concluded that zebrafish larvae have lower osmolality in their bodies than adult fish.The third project was dedicated to the investigation of the cellular structure of fish lenses. First, we developed a method to visualize an equatorial cross-sections of adult fish lenses. Than we used the method to examine lenses in two size groups of fish of the same species. We measured lens fiber thickness in four relative radial positions in the lens. Our measurements showed that fish lens fiber cells have the same thickness along the radius of the lens and in both size groups. The average thickness was much lower than in other vertebrates (Paper III).We followed up that study by measuring full thickness profile along the lens radius in nine fish species. The thickness of a fiber was independent from its radial position in the lens in all but one species. We observed that the average fiber thickness depends on species. Additionally, we developed a model for calculating historical lens fiber thicknesses necessary for the cells to reach their current refractive indices and thicknesses by cell compaction. The model showed that the cells would have to lose 66% of their volumes to reach their current sizes. This unlikely number and the constancy of cell thickness suggest that a different mechanism is at work. (Paper IV). Based on the findings from both papers, we conclude that, at least in fish, protein is transported inwards between denucleated fibers in the growing lens. The cells in the peripheral lens layers have synthetic capabilities and are most likely the source of those proteins.
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| 24. |
- Kozłowski, Tomasz M, et al.
(författare)
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Osmotic Concentration of Zebrafish (Danio rerio) Body Fluids is Lower in Larvae than in Adults
- 2018
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Ingår i: Zebrafish. - : Mary Ann Liebert Inc. - 1545-8547 .- 1557-8542. ; 15:1, s. 9-14
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Tidskriftsartikel (refereegranskat)abstract
- We intended to perform optical and structural measurements on larval zebrafish eyes at 5 days post fertilization, that is, the earliest age at which zebrafish show visually guided behavior. However, excised larval crystalline lenses deteriorated quickly if immersed in a medium that gives good results with adult lenses from a variety of fish species. We suspected that the larvae have body fluids of lower osmolality and tested a medium with 240 mOsm, which is 75% of the established adult value of 320 mOsm. The optical quality of freshly excised and immersed lenses was used to judge the osmotic matches. In addition, we tested how well the shape of the eye is preserved in fixatives of different osmolalities. In both cases, 240 mOsm produced the best results. Immersed lenses performed better and the fixed eyes had a more natural shape. Our findings indicate that zebrafish body fluids have lower osmolality in larvae than in adults. This is probably due to an unfavorable body surface-to-volume ratio and incompletely developed regulatory mechanisms. Body fluid osmolality deviating from the adult value has to be taken into account in optical and histological work.
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| 25. |
- Kozłowski, Tomasz M., et al.
(författare)
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Visualization of adult fish lens fiber cells
- 2019
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Ingår i: Experimental Eye Research. - : Elsevier BV. - 0014-4835. ; 181, s. 1-4
-
Tidskriftsartikel (refereegranskat)abstract
- The crystalline lens of a vertebrate eye is a gradient-index lens and grows throughout life by addition of new lens fiber cells in the periphery. In fish, the growing ball-shaped lens maintains sophisticated optical properties throughout life by maintaining the distribution of refractive index relative to the increasing radius of the lens. During this process, the central fibers must increase refractive index by increasing the cytosolic concentration of crystallin proteins. However, only the youngest, most peripheral lens fiber cells have the ability to synthesize proteins. Unfortunately, the hardness of fish lenses makes investigation of the cellular anatomy impossible with traditional histological methods. We have developed a method for visualizing lens fiber cells across the diameter of the lens in adult fish. The method relies on sectioning embedded lenses with a high-speed power saw and observing the cut surface with a scanning electron microscope (SEM). The combination of SEM and image analysis allowed for precise tracking of the positions of individual cell fiber cells. As an application of the method, we present a cell thickness profile, i.e. the distribution of cells thicknesses and their relative positions along the lens's radius. Combined with detailed optical studies, which by mathematical reasons only are possible on ball-shaped lenses, our method can lead to new insights into the mechanism governing the functional and cellular development of vertebrate lenses.
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| 26. |
- Kozlowski, Tomasz, et al.
(författare)
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Predicting actual reactor conditions : Why timedomain simulation is necessary for BWR stability
- 2013
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Ingår i: International Journal of Nuclear Energy Science and Technology. - 1741-6361. ; 7:4, s. 319-342
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 27. |
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| 28. |
- Kozlowski, Tomasz, et al.
(författare)
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QUALIFICATION OF THE RELAP5/PARCS CODE FOR BWR STABILITY EVENTS PREDICTION
- 2011
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 174:1, s. 51-63
-
Tidskriftsartikel (refereegranskat)abstract
- The present study is concerned with the capability of a coupled neutron-kinetic/thermal-hydraulic code system RELAP5/PARCS for the numerical prediction of global core stability condition and instability transients. The work is motivated by the need to assess the safety significance of a number of stability transients that trigger core instability and challenge reactor protection systems. The technical approach adopted is done both to learn from real stability events and to perform analysis of idealized well-defined transients in a real plant and core configuration. In this paper, we show that the code system can serve as a unique and powerful tool to provide a consistent and reasonably reliable prediction of stability boundary even in complex plant transients. However, the prediction quality of the instability transients, i.e., core behavior without scram namely, parameters of the limit cycle remains questionable. We identify, two main factors for future studies (two-phase flow regimes in oscillatory flow and algorithm for effective grouping of thermal-hydraulic channels) as key to enhancing the predictive capability of the existing coupled code system for boiling water reactor stability.
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| 29. |
- Kozlowski, Tomasz, et al.
(författare)
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Spatial Coupling for BWR Stability Analysis
- 2008
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Ingår i: Transactions of the American Nuclear Society. - : American Nuclear Society. ; , s. 603-605
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Konferensbidrag (refereegranskat)
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| 30. |
- Kozlowski, Tomasz, et al.
(författare)
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TRACE/PARCS VALIDATION FOR BWR STABILITY BASED ONOECD/NEA OSKARSHAMN-2 BENCHMARK
- 2011
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Konferensbidrag (refereegranskat)abstract
- On February 25, 1999, the Oskarshamn-2 NPP experienced a stability event, which culminated in diverging power oscillations with decay ratio greater than 1.3. The event was successfully modeled by TRACE/PARCS coupled code system and the details of the modeling and solution are described in the paper. The obtained results show excellent agreement with the plant data, capturing the entire behavior of the transient including onset of instability, growth of oscillation (decay ratio) and the oscillation frequency. The event allows coupled code validation for BWR with a real, challenging stability event, which challenges accuracy of neutron kinetics (NK), thermal-hydraulics (TH) and TH/NK coupling. The success of this work has demonstrated the ability of 3-D coupled code systems to capture the complex behavior of BWR stability events. The problem is 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. Interested participants are invited to contact authors for more information
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| 31. |
- Kubarev, Andrej, et al.
(författare)
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Design of BWR instability suppression system
- 2008
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Ingår i: International Conference on the Physics of Reactors 2008, PHYSOR 08. - 9781617821219 ; , s. 2062-2068
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Konferensbidrag (refereegranskat)abstract
- This paper explores the concept of instability suppression system and its performance in a BWR plant. The key idea adopted from the work of Aleksakov et al. (1980) is to utilize information provided by the in-core power monitoring detectors to guide movement of control rods in a way that suppress the global, regional and local instability. In the paper, effectiveness of a simplified suppression algorithm is characterized by implementing it on a real BWR model, using the RELAP5/PARCS coupled thermal-hydraulics and neutron kinetics code. Both forced power oscillations and realistic reactor transients (feedwater temperature transients, control rod drop) were analyzed. The results suggest that, without requiring any modifications for the in-reactor diagnostics and equipment, the proposed suppression system is capable of significantly mitigating the impact of core instability events on plant performance by maintaining the core parameters within the safe operational range.
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| 32. |
- Peltonen, Joanna, et al.
(författare)
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Development of effective algorithm for coupled thermal-hydraulic-neutron- kinetics analysis of reactivity transient
- 2011
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 176:2, s. 195-210
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Tidskriftsartikel (refereegranskat)abstract
- Analyses of nuclear reactor safety have increasingly required the coupling of full three-dimensional neutron-kinetics (NK) core models with system transient thermal-hydraulic (TH) codes. To produce results within a reasonable computing time, the coupled codes use different spatial descriptions of the reactor core. The TH code uses few, typically 5 to 20, TH channels that represent the core. The NK code uses the explicit node for each fuel assembly. Therefore, a spatial mapping of coarse grid TH and fine grid NK domain is necessary. However, improper mappings may result in the loss of valuable information, thus causing inaccurate prediction of safety parameters. The purpose of this investigation is to study the sensitivity of spatial coupling (channel refinement and spatial mapping) and develop recommendations for NK-TH mapping in the simulation of safety transients control rod drop, turbine trip, and feedwater transient combined with stability performance (minimum pump speed of recirculation pumps). The research methodology consists of a spatial coupling convergence study, as an increasing number of TH channels and different mapping schemes approach the reference case. The reference case consists of one TH channel per one fuel assembly. The comparison of results has been done under steady-state and transient conditions. The obtained results and conclusions are presented in this paper.
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| 33. |
- Peltonen, Joanna, et al.
(författare)
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Effective spatial mapping for coupled code analysis of thermal-hydraulics/neutron-kinetics of boiling water reactors
- 2014
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 63, s. 461-485
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Forskningsöversikt (refereegranskat)abstract
- Analyses of nuclear reactor safety have increasingly required coupling of full three dimensional neutron kinetics (NK) core models with system transient thermal-hydraulics (TH) codes. In order to produce results within a reasonable computing time, the coupled codes use two different spatial description of the reactor core. The TH code uses few, typically 5-20 TH channels, to represent the core. The NK code uses one explicit node for each fuel assembly. Therefore, a spatial mapping of a coarse grid TH and a fine grid NK domain is necessary. However, improper mappings may result in loss of valuable information, thus causing inaccurate prediction of safety parameters. In this article the study of the effectiveness of spatial coupling (channel -refinement and spatial mapping) and developed recommendations for NK/TH mapping are presented. The sensitivity of stability (measured by Decay Ratio and Frequency) to the different types of mapping schemes is analyzed against OECD/NEA Ringhals-1 Stability Benchmark data. Additionally, to increase the efficiency and applicability of spatial mapping convergence, a new mapping methodology is proposed. The new mapping approach is based on hierarchical clustering method; the method of unsupervised learning that is adopted in many different scientific fields, thanks to its flexibility and robustness. The proposed new mapping method is shown to be very successful for spatial coupling problem and can be fully automated allowing for significant time reduction in input preparation and mapping convergence study.
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| 34. |
- Peltonen, Joanna, et al.
(författare)
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Spatial coupling for coupled code safety analysis of BWR design-basis accidents
- 2008
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Konferensbidrag (refereegranskat)abstract
- Analyses of nuclear reactor safety have increasingly requiredcoupling of full three dimensional neutron kinetics(NK) core models with system transient thermal-hydraulics(TH) codes. To produce results within a reasonable computingtime, the coupled codes use different spatial descriptionof the reactor core. The TH code uses few, typically 5 to20 TH channels which represent the core. The NK code usesexplicit node for each fuel assembly. Therefore, a spatialmapping of coarse grid TH and fine grid NK domain is necessary.However, improper mappings may result in loss ofvaluable information, thus causing inaccurate prediction ofsafety parameters. The purpose of this paper is to study thesensitivity of spatial coupling (channel refinement and spatialmapping) and develop recommendations for NK-THmapping in simulation of safety transients.The research methodology consists of spatial couplingconvergence study, as increasing number of TH channelsand different mapping approach the reference case. Thereference case consists of 700 TH channels, which givesone TH channel per one fuel assembly. The comparison ofresults has been done under steady-state and transientconditions. Obtained results and conclusions are presentedin this paper.
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| 35. |
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| 36. |
- Racca, S., et al.
(författare)
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Trace code validation for BWR spray cooling injection and CCFL condition based on GÖTA facility experiments
- 2012
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Ingår i: Science and Technology of Nuclear Installations. - : Hindawi Limited. - 1687-6075 .- 1687-6083. ; 2012, s. 282987-
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Tidskriftsartikel (refereegranskat)abstract
- Best estimate codes have been used in the past thirty years for the design, licensing, and safety of NPP. Nevertheless, large efforts are necessary for the qualification and the assessment of such codes. The aim of this work is to study the main phenomena involved in the emergency spray cooling injection in a Swedish-designed BWR. For this purpose, data from the Swedish separate effect test facility GÖTA have been simulated using TRACE version 5.0 Patch 2. Furthermore, uncertainty calculations have been performed with the propagation of input errors method, and the identification of the input parameters that mostly influence the peak cladding temperature has been performed.
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| 37. |
- Roshan Ghias, Sean, et al.
(författare)
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A study of reactor systems during a loss of offsite electric power in Forsmark-1 Plant
- 2008
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Ingår i: Proceedings of 2007 International congress on advances in nuclear power plants (ICAPP 2007). - 9781604238716 ; , s. 2642-2651
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Konferensbidrag (refereegranskat)abstract
- On Tuesday the 25. of July 2006 at around 13:15, Forsmark-1 nuclear power plant experienced a loss of external power event, initiated by a short circuit in the offsite 400 kV switchyard. Due to voltage and frequency fluctuations that followed, together with additional component failures, two of the four auxiliary diesel generators did not start, causing loss of power in 2 of four redundant trains existing in the power plant. The loss of power in trains A,B resulted in reactor shutdown and abnormal intervention of safety systems. After 20 minutes, the water level inside the Reactor Pressure Vessel (RPV) decreased to 1,9 m above the reactor core, and the pressure inside the RPV decreased to 1,5 MPa. The aim of the present study is to evaluate the capabilities of U.S. NRC codes RELAP5 and MELCOR to simulate the Forsmark-1 event, and then to reconstruct the sequence of the event based on the known behavior of the plant systems, such as activation of depressurization valves. To examine the safety margin, it is of interest to address 'what if' questions related to this event, such as i) what if the operator would delay the recovery of the two failing diesel generators, and ii) what if all 4 diesel generators would fail. The results show that both RELAP5 and MELCOR codes are able to reproduce the system thermal-hydraulic behavior during such an event. The intervention of emergency cooling systems and effort of operators to start the remaining two auxiliary generators have prevented the core from becoming uncovered. The analysis also shows that even in case of failure of all 4 auxiliary generators, the timely action of the plan operator, as demonstrated in the action during the event, would prevent a core damage from occurring.
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| 38. |
- Sánchez, V. H., et al.
(författare)
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Qualification of the 3D Thermal Hydraulics Model of the Code System TRACE Based on plant data
- 2008
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Ingår i: Societe Francaise d'Energie Nucleaire - International Congress on Advances in Nuclear Power Plants - ICAPP 2007, "The Nuclear Renaissance at Work". - 9781604238716 ; , s. 1084-1092
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Konferensbidrag (refereegranskat)abstract
- The Institute of Reactor Safety is involved in the qualification of best-estimate coupled code systems for reactor safety evaluations since it is a key step toward improving their prediction capability and acceptability. In the frame of the WER-1000 Coolant Transient Benchmark PhaseI the coupled code RELAP5/PARCS has been extensively assessed. The Phase 2 of this benchmark- currently underway- is focused on both multidimensional thermal hydraulics phenomena within the reactor pressure vessel (RPV) such as coolant mixing and core physics. Hence it is an excellent opportunity to qualify the prediction capability of the new coupled code system TRACE/PARCS taking into account plant data obtained in the Kozloduy nuclear power plant unit 6. In addition a lose coupling of CFX with RELAP5 is applied for the posttest calculation of the coolant mixing experiment. The developed multidimensional models of the WER-1000 reactor pressure vessel as well as the performed calculations using these models are described in some detail. The predicted results are in good agreement with the data. It was demonstrated that the chosen 3D-nodalization of the RPV is adequate for the description of the coolant mixing phenomena in a WER-1000 reactor. In addition selected results of the code TRACE/PARCS for a postulated main steam line transient (MSLB) are given. The investigations have shown that the multidimensional neutronics and thermal hydraulic model developed for the RPV of the WER-1000 reactor are well qualified and consequently they are ready for their integration into a overall plant model so that the exercise 3 of the Phase 2 can be investigated as next.
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| 39. |
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| 40. |
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| 41. |
- Suchoszek, Joanna, et al.
(författare)
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RELAP5 and TRACE codes comparison and validation under steady-state and transient conditions on the basis of NUPEC data
- 2007
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Ingår i: 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12. - 0894480588 - 9780894480584
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Konferensbidrag (refereegranskat)abstract
- One-dimensional system codes are one of the main tools for the safety analysis of nuclear power plants. For BWR applications, it is of particular interest to know the performance of system codes in predicting void fraction, pressure drops, and, possibly, critical power in a wide range of conditions. The BFBT (BWR Full-Scale Fine-Mesh Bundle Tests) Benchmark [1], based on the NUPEC experiments, allows an accurate evaluation of the capabilities of the thermal-hydraulic codes in predicting the earlier mentioned quantities. The goal of this work is to evaluate the performance of RELAP5 and TRACE against the NUPEC experimental data. The fuel bundle employed in the benchmark has been modeled in the RELAP5 and TRACE input by a simple PIPE component using the fluid temperature and the mass flow rate as the inlet boundary condition and the pressure as the outlet boundary condition. We assessed the capability of RELAP5 and TRACE in predicting the void fraction, pressure drops and critical power in both steady-state and transient conditions. The obtained results were compared with the NUPEC measured data.
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| 42. |
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| 43. |
- Zerkak, Omar, et al.
(författare)
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Review of multi-physics temporal coupling methods for analysis of nuclear reactors
- 2015
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 84, s. 225-233
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 44. |
- Zerkak, Omar, et al.
(författare)
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Revisiting Temporal Accuracy in Neutronics/THCode Coupling Using the NURESIM LWRSimulation Platform
- 2011
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Ingår i: The 14th Internation Topical Meetingon Nuclear Reactor Thermalhydraulics (NURETH-14).
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Konferensbidrag (refereegranskat)abstract
- 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.
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