| 1. |
- Bestion, D., et al.
(författare)
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Multi-scale thermalhydraulic analyses performed in nuresim and nurisp projects
- 2012
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Ingår i: Proceedings of the 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference – 2012, Vol 4. - : ASME Press. - 9780791844984 ; , s. 581-590
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Konferensbidrag (refereegranskat)abstract
- The NURESIM and NURISP successive projects of the 6th and 7 th European Framework Programs joined the efforts of 21 partners for developing and validating a reference multi-physics and multi-scale platform for reactor simulation. The platform includes system codes, component codes, and also CFD or CMFD simulation tools. Fine scale CFD simulations are useful for a better understanding of physical processes, for the prediction of small scale geometrical effects and for solving problems that require a fine space and/or time resolution. Many important safety issues usually treated at the system scale may now benefit from investigations at a CFD scale. The Pressurized Thermal Shock is investigated using several simulation scales including Direct Numerical Simulation, Large Eddy Simulation, Very Large Eddy Simulation and RANS approaches. At the end a coupling of system code and CFD is applied. Condensation induced Water-Hammer was also investigated at both CFD and 1-D scale. Boiling flow in a reactor core up to Departure from Nucleate Boiling or Dry-Out is investigated at scales much smaller than the classical subchannel analysis codes. DNS was used to investigate very local processes whereas CFD in both RANS and LES was used to simulate bubbly flow and Euler-Lagrange simulations were used for annular mist flow investigations. Loss of Coolant Accidents are usually treated by system codes. Some related issues are now revisited at the CFD scale. in each case the progress of the analysis is summarized and the benefit of the multi-scale approach is shown.
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| 2. |
- Roelofs, F., et al.
(författare)
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Cross-cutting European Research for Single Phase Turbulence in Innovative Reactors
- 2010
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Ingår i: Proceedings of the 8<sup>th</sup> International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety.
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Konferensbidrag (refereegranskat)abstract
- Thermal-hydraulics is recognized as a key scientific subject in the development of different innovative nuclear reactor systems. From the thermal-hydraulic point of view, different innovative reactors are mainly characterized by their coolants (gas, water, liquid metals and molten salt). They result in different micro- and macroscopic behavior of flow and heat transfer and require specific models and advanced analysis tools. However, many common thermal-hydraulic issues are identified among various innovative nuclear systems. InEurope, such cross-cutting thermal-hydraulics issues are the subject of the 7th framework programme THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project which runs from 2010 untill 2014. This paper describes an important part of this project which will be devoted to single phase turbulence issues. To this respect, two main issues are identified and will be treated, i.e. non-unity Prandtl number turbulence and thermal fatigue in innovative nuclear systems.
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| 3. |
- Anghel, Ionut Gheorghe
(författare)
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Experimental Study of Post-Dryout Heat Transferin Annuli with Flow Obstacles
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An experimental study on post dryout heat transfer regime in annuli with flow obstacles was conducted in the High-pressure Water Test (HWAT) loop at the Royal Institute of Technology in Stockholm, Sweden. An annulus consisting of two concentric heated pipes (12.7x24.3) mm, with total heated length equal to 3650 mm was employed as a test section. Three kinds of flow obstacles were used: pin-spacers, cylindrical obstacles and grid obstacles. The experiments performed in the test section with pin-spacers only were considered as the reference case. In two consecutive sets of runs, additional obstacles were placed inside the flow channel while keeping the pin spacers in the same positions. In that way the net effect of obstacles on heat transfer was measured. The experimental investigations were performed in a wide range of the operational conditions: mass flux (500-1750) kg/(m2s), inlet subcooling (10-40) K and system pressure (5-7) MPa. The wall superheat was measured at 88 different axial positions (40 on the inner tube and 48 on the outer tube) for the conditions mentioned above. A local heat transfer coefficient was calculated based on the measured annulus wall temperatures and the saturated fluid (water) properties. The results show an enhancement of the heat transfer coefficient downstream of flow obstacles. The most significant influence has been observed in case of pin spacers. This result is consistent with blockage area of various obstacles, which was the highest in case of pin spacers. The data obtained in more than 200 runs were compared with two pre-dryout and post-dryout correlations. The correlations show a slight over-prediction of the heat transfer coefficient in both pre-dryout and post-dryout regions. The thesis contains a detailed description of experimental procedures as well as an analysis of the results of measurements.
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| 4. |
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| 5. |
- Anglart, D, et al.
(författare)
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Detecting and predicting changes in milk homogeneity using data from automatic milking systems.
- 2021
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Ingår i: Journal of Dairy Science. - : American Dairy Science Association. - 0022-0302 .- 1525-3198. ; 104:10, s. 11009-11017
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Tidskriftsartikel (refereegranskat)abstract
- To ensure milk quality and detect cows with signs of mastitis, visual inspection of milk by prestripping quarters before milking is recommended in many countries. An objective method to find milk changed in homogeneity (i.e., with clots) is to use commercially available inline filters to inspect the milk. Due to the required manual labor, this method is not applicable in automatic milking systems (AMS). We investigated the possibility of detecting and predicting changes in milk homogeneity using data generated by AMS. In total, 21,335 quarter-level milk inspections were performed on 5,424 milkings of 624 unique cows on 4 farms by applying visual inspection of inline filters that assembled clots from the separate quarters during milking. Images of the filters with clots were scored for density, resulting in 892 observations with signs of clots for analysis (77% traces or mild cases, 15% moderate cases, and 8% heavy cases). The quarter density scores were combined into 1 score indicating the presence of clots during a single cow milking and into 2 scores summarizing the density scores in cow milkings during a 30-h sampling period. Data generated from the AMS, such as milk yield, milk flow, conductivity, and online somatic cell counts, were used as input to 4 multilayer perceptron models to detect or predict single milkings with clots and to detect milking periods with clots. All models resulted in high specificity (98-100%), showing that the models correctly classified cow milkings or cow milking periods with no clots observed. The ability to successfully classify cow milkings or cow periods with observed clots had a low sensitivity. The highest sensitivity (26%) was obtained by the model that detected clots in a single milking. The prevalence of clots in the data was low (2.4%), which was reflected in the results. The positive predictive value depends on the prevalence and was relatively high, with the highest positive predictive value (72%) reached in the model that detected clots during the 30-h sampling periods. The misclassification rate for cow milkings that included higher-density scores was lower, indicating that the models that detected or predicted clots in a single milking could better distinguish the heavier cases of clots. Using data from AMS to detect and predict changes in milk homogeneity seems to be possible, although the prediction performance for the definitions of clots used in this study was poor.
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| 6. |
- Bestion, Dominique, et al.
(författare)
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Review of Available Data for Validation of Nuresim Two-Phase CFD Software Applied to CHF Investigations
- 2009
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Ingår i: Science and Technology of Nuclear Installations. - : Hindawi Limited. - 1687-6075 .- 1687-6083.
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Forskningsöversikt (refereegranskat)abstract
- The NURESIM Project of the 6th European Framework Program initiated the development of a new-generation common European Standard Software Platform for nuclear reactor simulation. The thermal-hydraulic subproject aims at improving the understanding and the predictive capabilities of the simulation tools for key two-phase flow thermal-hydraulic processes such as the critical heat flux (CHF). As part of a multi-scale analysis of reactor thermal-hydraulics, a two-phase CFD tool is developed to allow zooming on local processes. Current industrial methods for CHF mainly use the sub-channel analysis and empirical CHF correlations based on large scale experiments having the real geometry of a reactor assembly. Two-phase CFD is used here for understanding some boiling flow processes, for helping new fuel assembly design, and for developing better CHF predictions in both PWR and BWR. This paper presents a review of experimental data which can be used for validation of the two-phase CFD application to CHF investigations. The phenomenology of DNB and Dry-Out are detailed identifying all basic flow processes which require a specific modeling in CFD tool. The resulting modeling program of work is given and the current state-of-the-art of the modeling within the NURESIM project is presented.
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| 7. |
- Hallén Sandgren, C, et al.
(författare)
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Homogeneity density scores of quarter milk in automatic milking systems.
- 2021
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Ingår i: Journal of Dairy Science. - : American Dairy Science Association. - 0022-0302 .- 1525-3198. ; 104:9, s. 10121-10130
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Tidskriftsartikel (refereegranskat)abstract
- Milk quality and clinical mastitis in dairy cows are monitored by detecting visually abnormal milk. A standardized method to evaluate clots in milk and studies of the incidence and dynamics of clots in milk at the quarter level are lacking. We validated a method to score clot density in quarter milk samples and describe the prevalence and dynamics of the density scores between consecutive samplings and periods in 4 farms with automatic milking systems. Using in-line filters, we collected quarter milk samples at each milking during 3 periods of 30 h each in each farm. Clot density was scored based on coverage of the filter area as 0 (negative), 1 (trace), 2 (mild), 3 (moderate), 4 (heavy), and 5 (very heavy). The score for a specific quarter and milking is referred to as the quarter milking score (QMS). Three assessors independently scored 902 images of filter samples with a Fleiss kappa value of 0.72. In total, 21,202 quarter milk samples from 5,398 milkings of 621 cows were collected. Of the quarter filter samples, 2.4% had visible clots, distributed as mild (1.4%), moderate (0.6%), heavy (0.3%), and very heavy (<0.1%, n = 8). Cases with a cow period sum of QMS ≥ 4, corresponding to 9.4% of all periods, harbored 86% and 94% of all QMS of 2 to 5 and 3 to 5, respectively. Of these cases, cows sampled in all 3 periods and clots in only 1 period had a quarter period sum score ≥ 1 in 1.8 different quarters in average. Corresponding numbers for the cows with clots or traces in 2 or 3 periods were 2.2 and 2.5 different quarters, respectively. A QMS of 2 to 5 in the preceding milking increased the chance of a QMS >1 in the following milking, with an average chance of 38%. The probability of a QMS > 1 increased with increasing previous QMS, a higher sum of QMS during the milking period, longer milking interval, and higher lactation number, but decreased with increasing days in milk. Our study showed that the method of clot-density scoring is feasible to perform and reproducible for investigating the occurrence and dynamics of clots in milk. Elevated clot-density scores clustered within certain cows and cow periods and appeared in new quarters of the cows over time. The low recurrence of QMS of 1 and 2 within quarters indicated that QMS 3 could be a reasonable threshold for detecting quarters with abnormal milk that require further attention.
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| 8. |
- Lycklama a Nijeholt, J. A., et al.
(författare)
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DEVELOPMENT OF A HEAT TRANSFER CORRELATION FOR THE HPLWR FUEL ASSEMBLY BY MEANS OF CFD ANALYSIS
- 2011
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Ingår i: Proceedings of the 5th International Symposium on Supercritical Water-Cooled Reactors.
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Konferensbidrag (refereegranskat)abstract
- The High Performance Light Water Reactor (HPLWR) has been under development in the HPLWR phase-2 project funded by the European Union. The HPLWR project started September 2006 and ended February 2010. Work package 5 within this project involves the improved understanding of heat transfer, CFD model development and validation, and the prediction of the heat transfer rate in a HPLWR fuel assembly. USTUTT, KTH, NRG andFZK contributed to this work package. The overall objective of work package 5 was the development of a heat transfer correlation for the prediction of the heat transfer rate in the HPLWR fuel assembly by means of CFD analyses. In the HPLWR fuel assembly, a helical wire has been selected as spacer and mixing device. This wire-wrap imposed a significant challenge in the development of the geometrical models for the CFD analyses. Due to thewire-wrap it was not possible to model a full fuel assembly consisting of 40 rods. Therefore,an alternative procedure has been adopted to develop a heat transfer correlation for the HPLWR fuel assembly. This procedure involved the definition of correction factors accounting for the effect of the rod bundle geometry and the wire-wrap spacer with respect toa smooth circular tube with super-critical water.The present paper describes the procedure followed in work package 5 of the HPLWRphase-2 project for the development of a heat transfer correlation for the HPLWR fuel assembly design and presents the derivation of the applied correction factors from a large set of CFD analyses for different representative geometries like an annulus, a single sub-channeland a 4 rod-bundle, all with and without inclusion of the wire wrap.
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| 9. |
- Schulenberg, T., et al.
(författare)
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European supercritical water cooled reactor
- 2011
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 241:9, s. 3505-3513
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Tidskriftsartikel (refereegranskat)abstract
- The High Performance Light Water Reactor (HPLWR), how the European Supercritical Water Cooled Reactor is called, is a pressure vessel type reactor operated with supercritical water at 25 MPa feedwater pressure and 500 degrees C average core outlet temperature. It is designed and analyzed by a European consortium of 10 partners and 3 active supporters from 8 Euratom member states in the second phase of the HPLWR project. Most emphasis has been laid on a core with a thermal neutron spectrum, consisting of small fuel assemblies in boxes with 40 fuel pins each and a central water box to improve the neutron moderation despite the low coolant density. Peak cladding temperatures of the fuel rods have been minimized by heating up the coolant in three steps with intermediate coolant mixing. The containment design with its safety and residual heat removal systems is based on the latest boiling water reactor concept, but with different passive high pressure coolant injection systems to cause a forced convection through the core. The design concept of the steam cycle is indicating the envisaged efficiency increase to around 44%. Moreover, it provides the constraints to design the components of the balance of the plant. The project is accompanied by numerical studies of heat transfer of supercritical water in fuel assemblies and by material tests of candidate cladding alloys, performed by the consortium and supported by additional tests of the Joint Research Centre of the European Commission. Besides the scientific and technical progress, the HPLWR project turned out to be most successful in training the young generation of nuclear engineers in the technologies of light water reactors. More than 20 bachelor or master theses and more than 10 doctoral theses on HPLWR technologies have been submitted at partner organizations of this consortium since the start of this project.
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| 10. |
- Starflinger, J., et al.
(författare)
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European research activities within the project : "High Performance Light Water Reactor Phase 2" (HPLWR Phase 2)
- 2008
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Ingår i: Int. Congr. Adv. Nucl. Power Plants - ICAPP, "Nucl. Renaiss. Work". - 9781604238716 ; , s. 867-876
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Konferensbidrag (refereegranskat)abstract
- The High Performance Light Water Reactor (HPLWR) is a Light Water Reactor (LWR) operating at supercritical pressure (25MPa). It belongs to the six reactors currently being investigated under the framework of the Generation IV International Forum. The most visible advantage of the HPLWR shall be the low construction costs in the order of1000€/kWe, because of size reduction of components and buildings compared to current LWR, and the low electricity production costs which are targeted at 3-4cents/kWh. In Europe, investigations on the HPLWR have been integrated into a joint research project, called High Performance Light Water Reactor Phase 2 (HPLWR Phase 2), which is co-funded by the European Commission. Within 42 months, ten partners from eight European countries working on critical scientific issues shall show the feasibility of the HPLWR concept. The final goal is to assess the future potential of this reactor in the electricity market.
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