| 1. |
- Bandini, G., et al.
(författare)
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Assessment of systems codes and their coupling with CFD codes in thermal-hydraulic applications to innovative reactors
- 2015
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 281, s. 22-38
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Tidskriftsartikel (refereegranskat)abstract
- The THINS project of the 7th Framework EU Program on nuclear fission safety is devoted to the investigation of crosscutting thermal hydraulic issues for innovative nuclear systems. A significant effort in the project has been dedicated to the qualification and validation of system codes currently employed in thermal hydraulic transient analysis for nuclear reactors. This assessment is based either on already available experimental data, or on the data provided by test campaigns carried out in the frame of THINS project activities. Data provided by TALL and CIRCE facilities were used in the assessment of system codes for HLM reactors, while the PHENIX ultimate natural circulation test was used as reference for a benchmark exercise among system codes for sodium-cooled reactor applications. In addition, a promising grid-free pool model based on proper orthogonal decomposition is proposed to overcome the limits shown by the thermal hydraulic system codes in the simulation of pool-type systems. Furthermore, multi-scale system-CFD solutions have been developed and validated for innovative nuclear system applications. For this purpose, data from the PHENIX experiments have been used, and data are provided by the tests conducted with new configuration of the TALL-3D facility, which accommodates a 3D test section within the primary circuit. The TALL-3D measurements are currently used for the validation of the coupling between system and CFD codes.
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| 2. |
- Moreau, V., et al.
(författare)
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Pool CFD modelling : lessons from the SESAME project
- 2019
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Ingår i: Nuclear Engineering and Design. - : ELSEVIER SCIENCE SA. - 0029-5493 .- 1872-759X. ; 355
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Tidskriftsartikel (refereegranskat)abstract
- The current paper describes the Computational Fluid-Dynamics (CFD) modelling of Heavy Liquid Metal (HLM) flows in a pool configuration and in particular how this is approached within the Horizon 2020 SESAME project. SESAME's work package structure, based on a systematic approach of redundancy and diversification, is explained along with its motivation. The main achievements obtained and the main lessons learned during the project are illustrated. The paper focuses on the strong coupling between the experimental activities and CFD simulations performed within the SESAME project. Two different HLM fluids are investigated: pure lead and Lead-Bismuth Eutectic. The objective is to make CFD a valid instrument used during the design of safe and innovative Gen-IV nuclear plants. Some effort has also been devoted to Proper Orthogonal Decomposition with Galerkin projection modelling (POD-Galerkin), a reduced order model suited for Uncertainty Quantification that operates by post-processing CFD results. Assessment of Uncertainty highly improves the reliability of CFD simulations. Dedicated experimental campaigns on heavily instrumented facilities have been conceived with the specific objective to build a series of datasets suited for the calibration and validation of the CFD modelling. In pool configuration, the attention is focused on the balance between conductive and convective heat transfer phenomena, on transient test-cases representative of incidental scenarios and on the possible occurrence of solidification phenomena. Four test sections have been selected to generate the datasets: (i) the CIRCE facility from ENEA, (ii) the TALL-3D pool test section from KTH, (iii) the TALL-3D Solidification Test Section (STS) from KTH and (iv) the SESAME Stand facility from CVR. While CIRCE and TALL-3D were existing facilities, the STS and SESAME Stand facility have been conceived, built and operated within the project, heavily relying on the use of CFD support. Care has been taken to ensure that almost all tasks were performed by at least two partners. Specific examples are given on how this strategy has allowed to uncover flaws and overcome pitfalls. Furthermore, an overview of the performed work and the achieved results is presented, as well as remaining or new uncovered issues. Finally, the paper is concluded with a description of one of the main goals of the SESAME project: the construction of the Gen-IV ALFRED CFD model and an investigation of its general circulation.
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| 3. |
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| 4. |
- Sujan, Ayesha C., et al.
(författare)
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A Genetically Informed Study of the Associations Between Maternal Age at Childbearing and Adverse Perinatal Outcomes
- 2016
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Ingår i: Behavior Genetics. - New York, USA : Springer. - 0001-8244 .- 1573-3297. ; 46:3, s. 431-456
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Tidskriftsartikel (refereegranskat)abstract
- We examined associations of maternal age at childbearing (MAC) with gestational age and fetal growth (i.e., birth weight adjusting for gestational age), using two genetically informed designs (cousin and sibling comparisons) and data from two cohorts, a population-based Swedish sample and a nationally representative United States sample. We also conducted sensitivity analyses to test limitations of the designs. The findings were consistent across samples and suggested that, associations observed in the population between younger MAC and shorter gestational age were confounded by shared familial factors; however, associations of advanced MAC with shorter gestational age remained robust after accounting for shared familial factors. In contrast to the gestational age findings, neither early nor advanced MAC was associated with lower fetal growth after accounting for shared familial factors. Given certain assumptions, these findings provide support for a causal association between advanced MAC and shorter gestational age. The results also suggest that there are not causal associations between early MAC and shorter gestational age, between early MAC and lower fetal growth, and between advanced MAC and lower fetal growth.
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| 5. |
- Bramson, L. M., et al.
(författare)
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The association between childhood relocations and subsequent risk of suicide attempt, psychiatric problems, and low academic achievement
- 2016
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Ingår i: Psychological Medicine. - New York, USA : Cambridge University Press. - 0033-2917 .- 1469-8978. ; 46:5, s. 969-979
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Tidskriftsartikel (refereegranskat)abstract
- Background: Given the frequency with which families change residences, the effects of childhood relocations have gained increasing research attention. Many researchers have demonstrated that childhood relocations are associated with a variety of adverse outcomes. However, drawing strong causal claims remains problematic due to uncontrolled confounding factors.Method: We utilized longitudinal, population-based Swedish registers to generate a nationally representative sample of offspring born 1983-1997 (n = 1 510 463). Using Cox regression and logistic regression, we examined the risk for numerous adverse outcomes after childhood relocation while controlling for measured covariates. To account for unmeasured genetic and environmental confounds, we also compared differentially exposed cousins and siblings.Results: In the cohort baseline model, each annual relocation was associated with risk for the adverse outcomes, including suicide attempt [hazard ratio (HR) 1.19, 95% confidence interval (CI) 1.19-1.20]. However, when accounting for offspring and parental covariates (HR 1.08, 95% CI 1.07-1.09), as well as genetic and environmental confounds shared by cousins (HR 1.07, 95% CI 1.05-1.09) and siblings (HR 1.00, 95% CI 0.97-1.04), the risk for suicide attempt attenuated. We found a commensurate pattern of results for severe mental illness, substance abuse, criminal convictions, and low academic achievement.Conclusions: Previous research may have overemphasized the independent association between relocations and later adverse outcomes. The results suggest that the association between childhood relocations and suicide attempt, psychiatric problems, and low academic achievement is partially explained by genetic and environmental confounds correlated with relocations. This study demonstrates the importance of using family-based, quasi-experimental designs to test plausible alternate hypotheses when examining causality.
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| 6. |
- Class, Q. A., et al.
(författare)
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Offspring psychopathology following preconception, prenatal and postnatal maternal bereavement stress
- 2014
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Ingår i: Psychological Medicine. - New York, USA : Cambridge University Press. - 0033-2917 .- 1469-8978. ; 44:1, s. 71-84
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Tidskriftsartikel (refereegranskat)abstract
- Background: Preconception, prenatal and postnatal maternal stress is associated with increased offspring psychopathology, but findings are inconsistent and need replication. We estimated associations between maternal bereavement stress and offspring autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), bipolar disorder, schizophrenia, suicide attempt and completed suicide.Method: Using Swedish registers, we conducted the largest population-based study to date examining associations between stress exposure in 738,144 offspring born 1992-2000 for childhood outcomes and 2,155,221 offspring born 1973-1997 for adult outcomes with follow-up to 2009. Maternal stress was defined as death of a first-degree relative during (a) the 6 months before conception, (b) pregnancy or (c) the first two postnatal years. Cox proportional survival analyses were used to obtain hazard ratios (HRs) in unadjusted and adjusted analyses.Results: Marginal increased risk of bipolar disorder and schizophrenia following preconception bereavement stress was not significant. Third-trimester prenatal stress increased the risk of ASD [adjusted HR (aHR) 1.58, 95% confidence interval (CI) 1.15-2.17] and ADHD (aHR 1.31, 95% CI 1.04-1.66). First postnatal year stress increased the risk of offspring suicide attempt (aHR 1.13, 95% CI 1.02-1.25) and completed suicide (aHR 1.51, 95% CI 1.08-2.11). Bereavement stress during the second postnatal year increased the risk of ASD (aHR 1.30, 95% CI 1.09-1.55).Conclusions: Further research is needed regarding associations between preconception stress and psychopathological outcomes. Prenatal bereavement stress increases the risk of offspring ASD and ADHD. Postnatal bereavement stress moderately increases the risk of offspring suicide attempt, completed suicide and ASD. Smaller previous studies may have overestimated associations between early stress and psychopathological outcomes.
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| 7. |
- Dietrich, P., et al.
(författare)
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Coupling of melcor with the pecm for improved modelling of a core melt in the lower plenum
- 2015
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Ingår i: International Conference on Nuclear Engineering, Proceedings, ICONE. - : JSME.
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Konferensbidrag (refereegranskat)abstract
- MELCOR contains a coupling interface based on the MPI-Standard, which enables the communication to other codes such as RELAP5 or GASFLOW. However a detailed knowledge of this coupling interface in MELCOR is necessary to use this possibility. Therefore, at the KIT the software tool DINAMO (Direct Interface for Adding Models) has been developed. This program contains the coupling routines as well as an interface to communicate with other programs. Using DINAMO it is also possible to utilize new or enhanced models for phenomena, which occur during a severe accident in a nuclear power plant, in MELCOR without modification of the MELCOR source code. In the present work MELCOR calculations of experiments in the LIVE-Facility are presented. The LIVE-Facility is used to simulate the behavior of a melt in the lower plenum of a reactor pressure vessel (RPV). For these calculations we coupled MELCOR via DINAMO with the Phase-Change Effective Convectivity Model (PECM), which has been developed at the KTH in Stockholm. Using the PECM it is possible to improve the prediction of a core melt in the lower plenum of a RPV in case of a core melt accident.
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| 8. |
- Dietrich, P., et al.
(författare)
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Extension of the MELCOR code for analysis of late in-vessel phase of a severe accident
- 2015
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Ingår i: IYCE 2015 - Proceedings. - : IEEE conference proceedings. - 9781467371728
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Konferensbidrag (refereegranskat)abstract
- The simulation of severe accidents in nuclear power plants with system codes is a powerful tool to improve the safety measures to prevent severe accidents. The further development of severe accident codes is part of current research. MELCOR, as the leading nuclear safety code, provides the possibility to be coupled to other codes. A detailed knowledge of this coupling interface is necessary to use this possibility. Therefore, the software tool DINAMO, which contains the coupling routines and an interface to communicate with other programs, was developed. Using DINAMO it is possible to utilize new models for specific phenomena in MELCOR. In the present work the Phase-Change Effective Convectivity Model was coupled using the CFD-software OpenFOAM and DINAMO to MELCOR to improve the prediction of molten core material in the lower plenum of a reactor pressure vessel. The simulation results were compared to the experimental findings of the LIVE-facility.
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| 9. |
- D'Onofrio, Brian M., et al.
(författare)
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Translational Epidemiologic Approaches to Understanding the Consequences of Early-Life Exposures
- 2016
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Ingår i: Behavior Genetics. - New York, USA : Springer. - 0001-8244 .- 1573-3297. ; 46:3, s. 315-328
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Forskningsöversikt (refereegranskat)abstract
- Prominent developmental theories posit a causal link between early-life exposures and later functioning. Yet, observed associations with early exposures may not reflect causal effects because of genetic and environmental confounding. The current manuscript describes how a systematic series of epidemiologic analyses that combine several genetically-informative designs and statistical approaches can help distinguish between competing theories. In particular, the manuscript details how combining the use of measured covariates with sibling-comparisons, cousin-comparisons, and additional designs can help elucidate the sources of covariation between early-life exposures and later outcomes, including the roles of (a) factors that are not shared in families, including a potential causal effect of the exposure; (b) carryover effects from the exposure of one child to the next; and (c) familial confounding. We also describe key assumptions and how they can be critically evaluated. Furthermore, we outline how subsequent analyses, including effect decomposition with respect to measured, plausible mediators, and quantitative genetic models can help further specify the underlying processes that account for the associations between early-life exposures and offspring outcomes.
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| 10. |
- Ginsberg, Ylva, et al.
(författare)
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Maternal infection requiring hospitalization during pregnancy and attention-deficit hyperactivity disorder in offspring : a quasi-experimental family-based study
- 2019
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Ingår i: Journal of Child Psychology and Psychiatry. - : Blackwell Publishing. - 0021-9630 .- 1469-7610. ; 60:2, s. 160-168
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Maternal infection during pregnancy (IDP) has been associated with increased risk of attention-deficit/hyperactivity disorder (ADHD) in offspring. However, infection is associated with social adversity, poor living conditions and other background familial factors. As such, there is a need to rule out whether the observed association between maternal IDP and ADHD might be attributed to such confounding.METHODS: This nationwide population-based cohort study using a family-based, quasi-experimental design included 1,066,956 individuals born in Sweden between 1992 and 2002. Data on maternal IDP (bacterial or viral) requiring hospitalization and ADHD diagnosis in offspring were gathered from Swedish National Registers, with individuals followed up through the end of 2009. Ordinary and stratified Cox regression models were used for estimation of hazard ratios (HRs) and several measured covariates were considered. Cousin- and sibling-comparisons accounted for unmeasured genetic and environmental factors shared by cousins and siblings.RESULTS: In the entire population, maternal IDP was associated with ADHD in offspring (HR = 2.31, 95% CI = 2.04-2.61). This association was attenuated when accounting for measured covariates (HR = 1.86, 95% CI = 1.65-2.10). The association was further attenuated when adjusting for unmeasured factors shared between cousins (HR = 1.52, 95% CI = 1.12-2.07). Finally, the association was fully attenuated in sibling comparisons (HR = 1.03, 95% CI = 0.76-1.41).CONCLUSIONS: This study suggests that the association between maternal IDP and offspring ADHD is largely due to unmeasured familial confounding. Our results underscore the importance of adjusting for unobserved familial risk factors when exploring risk factors for ADHD.
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