| 1. |
- Bellenguez, Celine, et al.
(författare)
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Genome-wide association study identifies a variant in HDAC9 associated with large vessel ischemic stroke
- 2012
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1546-1718 .- 1061-4036. ; 44:3, s. 141-328
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Tidskriftsartikel (refereegranskat)abstract
- Genetic factors have been implicated in stroke risk, but few replicated associations have been reported. We conducted a genome-wide association study (GWAS) for ischemic stroke and its subtypes in 3,548 affected individuals and 5,972 controls, all of European ancestry. Replication of potential signals was performed in 5,859 affected individuals and 6,281 controls. We replicated previous associations for cardioembolic stroke near PITX2 and ZFHX3 and for large vessel stroke at a 9p21 locus. We identified a new association for large vessel stroke within HDAC9 (encoding histone deacetylase 9) on chromosome 7p21.1 (including further replication in an additional 735 affected individuals and 28,583 controls) (rs11984041; combined P = 1.87 x 10(-11); odds ratio (OR) = 1.42, 95% confidence interval (CI) = 1.28-1.57). All four loci exhibited evidence for heterogeneity of effect across the stroke subtypes, with some and possibly all affecting risk for only one subtype. This suggests distinct genetic architectures for different stroke subtypes.
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| 2. |
- Kouhia, Virpi, et al.
(författare)
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Benchmark exercise on SBLOCA experiment of PWR PACTEL facility
- 2013
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 59, s. 149-156
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Tidskriftsartikel (refereegranskat)abstract
- The PWR PACTEL benchmark exercise was organized in Lappeenranta, Finland by Lappeenranta University of Technology. The benchmark consisted of two phases, i.e. a blind and an open calculation task. Seven organizations from the Czech Republic, Germany, Italy, Sweden and Finland participated in the benchmark exercise, and four system codes were utilized in the benchmark simulation tasks. Two workshops were organized for launching and concluding the benchmark, the latter of which involved presentations of the calculation results as well as discussions on the related modeling issues. The chosen experiment for the benchmark was a small break loss of coolant accident experiment which was performed to study the natural circulation behavior over a continuous range of primary side coolant inventories. For the blind calculation task, the detailed facility descriptions, the measured pressure and heat losses as well as the results of a short characterizing transient were provided. For the open calculation task part, the experiment results were released. According to the simulation results, the benchmark experiment was quite challenging to model. Several improvements were found and utilized especially for the open calculation case. The issues concerned model construction, heat and pressure losses impact, interpreting measured and calculated data, non-condensable gas effect, testing several condensation and CCFL correlations, sensitivity studies, as well as break modeling. There is a clear need for user guidelines or for a collection of best practices in modeling for every code. The benchmark offered a unique opportunity to test the best practices and solutions in modeling and analyzing tasks as well as a possibility to increase knowledge about the interpretation of test results. The benchmark exercise served as a practical and rewarding forum to discuss the needs, problems and possibilities in the analysis and in producing useful data with an experiment facility. The workshops provided an advantageous site for interaction of the code users and the experimenters.
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| 3. |
- 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
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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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| 4. |
- Kozlowski, Tomasz, et al.
(författare)
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QUALIFICATION OF THE RELAP5/PARCS CODE FOR BWR STABILITY EVENTS PREDICTION
- 2011
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 174:1, s. 51-63
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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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| 5. |
- 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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| 6. |
- 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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| 7. |
- Peltonen, Joanna, 1982-
(författare)
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Development of Effective Algorithm for Coupled Thermal-Hydraulics – Neutron-Kinetics Analysis of Reactivity Transient
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)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. To produce results within a reasonable computing time, the coupled codes use different spatial description of the reactor core. The TH code uses few, typically 5 to 20 TH channels, which represent the core. The NK code uses 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 loss of valuable information, thus causing inaccurate prediction of safety parameters. The purpose of this thesis is to study the sensitivity of spatial coupling (channel refinement and spatial mapping) and develop recommendations for NK-TH mapping in simulation of safety transients – Control Rod Drop, Turbine Trip, Feedwater Transient combined with stability performance (minimum pump speed of recirculation pumps). The research methodology consists of spatial coupling convergence study, as increasing number of TH channels and different mapping 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. Obtained results and conclusions are presented in this licentiate thesis.
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| 8. |
- 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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| 9. |
- Peltonen, Joanna, 1982-
(författare)
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Effective Spatial Mapping for Coupled Code Analysis of Thermal–Hydraulics/Neutron–Kinetics of Boiling Water Reactors
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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 to 20 TH channels, which represent the core. The NK code uses explicit one 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.The purpose of this thesis is to study the effectiveness of spatial coupling (channel refinement and spatial mapping) and develop recommendations for NK/TH mapping in simulation of safety transients. Additionally, 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.The research methodology consists of spatial coupling convergence study, by increasing the number of TH channels and varying mapping approaches, up to and including the reference case. The reference case consists of one-to-one mapping: one TH channel per one fuel assembly. The comparisons of the results are done for steady–state and transient results. In this thesis mapping (spatial coupling) definition is formed and all the existing mapping approaches were gathered, analyzed and presented. Additionally, to increase the efficiency and applicability of spatial mapping convergence, a new mapping methodology has been proposed. The new mapping approach is based on hierarchical clustering method; the method of unsupervised learning that is adopted by many researchers in many different scientific fields, thanks to its flexibility and robustness. The proposed new mapping method turns out to be very successful for spatial coupling problem and can be fully automatized allowing for significant time reduction in mapping convergence study.The steady–state results obtained from three different plant models for all the investigated cases are presented. All models achieved well converged steady–state and local parameters were compared and it was concluded that solid basis for further transient analysis was found. Analyzing the mapping performance, the best predictions for steady–state conditions are the mappings that include the power peaking factor feature alone or with any combination of other features. Additionally it is of value to keep the core symmetry (symmetry feature). The big part of this research is devoted to transient analysis. The selection of transients was done such that it covers a wide range of transients and gathered knowledge may be used for other types of transients. As a representative of a local perturbation, Control Rod Drop Accident was chosen. A specially prepared Feedwater Transient was investigated as a regional perturbation and a Turbine Trip is an example of a global one. In the case of local perturbation, it has been found that a number of TH channels is less important than the type of mapping, so a high number of TH channels does not guarantee improved results. To avoid unnecessary averaging and to obtain the best prediction, hot channel and core zone where accident happens should be always separated from the rest. The best performance is achieved with mapping according power peaking factors, and therefore this one is recommended for such type of perturbation.The regional perturbation has been found to be more challenging than the others. This kind of perturbation is strongly dependent on mapping type that affects the power increase rate, SCRAM time, onset of instability, development of limit cycle, etc. It has been also concluded that a special effort is needed for input model preparation. In contrast to the regional perturbation, the global perturbation is found to be the least demanding transient. Here, the number of TH channels and type of mapping do not have significant impact on average plant behaviour – general plant response is always well recreated. A special effort has also been paid to investigate the core stability performance, in both global and regional mode. It has been found that in case of unstable cores, a low number of TH channels significantly suppresses the instability. For these cases number of TH channels is very important and therefore at least half of the core has to be modeled to have a confidence in predicted DR and FR. In case of regional instability in order to get correct performance of out-of-phase oscillations, it is recommended to use full-scale model. If this is not possible, the mapping which is a mixture of 1st power mode and power peaking factors, should be used.The general conclusions and recommendations are summarized at the end of this thesis. Development of these recommendations was one of the purposes of this investigation and they should be taken into consideration while designing new coupled TH/NK models and choosing mapping strategy for a new transient analysis.
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| 10. |
- Peltonen, Joanna, et al.
(författare)
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Spatial coupling for coupled code safety analysis of BWR design-basis accidents
- 2008
-
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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