| 1. |
- Adamsson, Carl, et al.
(författare)
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A reinterpretation of measurements in developing annular two-phase flow
- 2011
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 241:11, s. 4562-4567
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of developing films in adiabatic high pressure steam-water flow in annular geometry have been reanalyzed and compared to a linearized film-flow model. The development rate of the outer film could be determined with good accuracy in four cases. In one case it was also possible to conclude that the inner film develops faster than the outer one. When compared to the linearized model, these observations show that the deposition rate has to be almost independent of the drop concentration at the investigated conditions. Furthermore, any significant deposition by direct impaction of drops can be excluded as it would couple the development of the two films. These conclusions are quite general and do not depend on the use of any particular correlation for the deposition or entrainment rates. Finally, a rough estimate of the deposition rate was possible, confirming that deposition rates are considerably lower at high pressure steam-water flows than in air-water flows.
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| 2. |
- Adamsson, Carl, et al.
(författare)
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An investigation of cross-section geometry effects on the deposition rate in annular two-phase flows with a Lagrangian model
- 2007
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Ingår i: Proceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12. - 9780894480584 - 0894480588
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Konferensbidrag (refereegranskat)abstract
- The motion of liquid drops in annular two-phase flow in pipes, annuli and subchannels has been investigated with a model based on Lagrangian particle tracking. The results confirm that large drops may deposit by direct impaction. It is also demonstrated that the deposition rate does not differ significantly between pipes and subchannels except for very large drops, which deposit slower in subchannels. Furthermore the Saffman lift force is shown to have a large impact on the results but it is questionable of the standard formulation is applicable to the drops considered here. Finally it is concluded that accurate modeling of high pressure steam-water flows requires a model for drop-drop collisions.
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| 3. |
- Adamsson, Carl, 1976-
(författare)
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Dryout and Power Distribution Effects in Boiling Water Reactors
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Film flow measurements at several axial positions in round pipes with variousaxial power distributions are presented for conditions corresponding to normaloperation of a BWR. It is confirmed that the film flow rate approaches zero atthe onset of dryout. Selected phenomenological models of annular two-phaseflow are shown to reasonably reproduce the measurements. It is concluded thatmodels are in better agreement with measurements if terms corresponding topossible boiling induced entrainment are excluded. A method to perform film flow analysis in subchannels as a post-processto a standard two-field subchannel code is suggested. It is shown that thisapproach may yield accurate prediction of dryout power in rod bundles to alow computational cost and that the influence of the power distribution is wellpredicted by the model.
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| 4. |
- Adamsson, Carl, et al.
(författare)
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Dryout predictions in bwr fuel assemblies with spacers
- 2004
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Ingår i: Proceedings of the Sixth International Conference on Nuclear Thermal-Hydraulics, Operation and Safety.
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Konferensbidrag (refereegranskat)abstract
- A new spacer model has been implemented into the subchannel code Mona-3 and validated against dryout experiments in various rod bundles with different number of spacers and different spacer designs. The spacer-induced deposition enhancement is captured by proper modeling of the turbulence intensity downstream of a spacer.The Mona-3 code with the new spacer model captures spacer effects in a correct manner. Both the effect of the number of spacers and the effect of the spacer design are predicted correctly. In particular, the critical power difference between 24-rod bundles with 6 and with 7 spacers is measured to be larger than the difference between 25-rod bundles with 6 and with 7 spacers. This experimental finding is well captured with the Mona-3 code with the present spacer model.
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| 5. |
- Adamsson, Carl, et al.
(författare)
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Eperimental Investigation of the Liquid Film for Annular Flow in a Tube with Various Axial Power Distributions
- 2005
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Ingår i: NURETH 11, Avignon, France, October 2–6, 2005.
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Konferensbidrag (refereegranskat)abstract
- This paper was published when the measurements with non-uniform powerdistribution were still ongoing. Therefore only the measurements with uniformand top-peaked power profiles were included. The paper compares the measured data with deposition and entrainmentmodels by Hewitt & Govan (1990) and Okawa et al. (2003). These models are also discussed in Sections 4.2.1 and 4.2.2. The issue of a correct boundarycondition at the onset of annular flow was avoided by starting the integrationof the film flow model from the most upstream measurement point. In this way the net mass exchange rate (deposition less entrainment) could be studied without any initial bias from the boundary condition.The entrainment correlation proposed by Okawa et al. (2003) included a heat flux dependent term to account for boiling entrainment (Section 4.2.2). Paper 2 concludes that the model agrees better with measurements if this term is omitted. The result suggests that boiling entrainment may not be an important effect at the investigated conditions.
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| 6. |
- Adamsson, Carl, et al.
(författare)
-
Film flow measurements for high-pressure diabatic annular flow in tubes with various axial power distributions
- 2006
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 236:23, s. 2485-2493
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of film flow rates in diabatic annular flow in tubes with various axial power distributions were carried out in the high-pressure two-phase flow loop at the Royal Institute of Technology (KTH), Sweden. The measurements were performed at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m(2)s. Four different axial power distributions were used and the film mass flow was measured at 7 axial locations for each set of boundary conditions. The results show that the outlet peaked distribution gives less film than the inlet peaked one. This result is consistent with well known trends from measurements of dryout power. The measurements also show that the film flow at the onset of dryout is very small at investigated conditions in agreement with earlier studies. Finally it is shown that the present data is well predicted by two selected phenomenological models of annular flow.
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| 7. |
- Adamsson, Carl, et al.
(författare)
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Influence of Axial Power Distribution on Dryout : Film-Flow Models and Experiments
- 2010
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 240:6, s. 1495-1505
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Tidskriftsartikel (refereegranskat)abstract
- The influence of axial power distributions on dryout occurrence in nuclear fuel assemblies has been studied extensively for several decades. Even though it is well known that axial power shapes which may significantly vary in nuclear reactors during their operation significantly change the dryout power level, this particular influence is rather difficult to capture with current correlations. In this paper it is shown that this influence can be captured using a phenomenological liquid film model coupled to a standard sub-channel code. The model has been applied to various geometries, including a round pipe, as well as 5 x 5 and 8 x 8 fuel rod assemblies, and highly accurate predictions have been obtained.
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| 8. |
- Adamsson, Carl, 1976-
(författare)
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Measurements of Film Flow Rate in Heated Tubes with Various Axial Power Distributions
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Measurements of film mass flow rate for annular, diabatic steam-water flow in tubes are presented. The measurements were carried out with four axial power distributions and at several axial positions at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m2s. The results show that the influence of the axial power distribution on the dryout power corresponds to a consistent tendency in the film flow rate and that the film tends to zero when dryout is approached. Furthermore it is demonstrated that two selected phenomenological models of annular flow well predict the present data. A model for additional entrainment due to boiling is shown to degrade the predictions.
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| 9. |
- Adamsson, Carl, et al.
(författare)
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Measurements of the Liquid Film Flow Rate in High Pressure Annular Flow with Various Axial Power Distributions
- 2005
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Ingår i: HEAT 2005, Gdansk, Poland, June 26–30, 2005.
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Konferensbidrag (refereegranskat)abstract
- This paper presents film flow measurement technique and the results with uniform power distribution. Based on these measurements it is possible to estimate the critical film thickness. The measured film thickness was plotted versus steam quality and slightlyextrapolated up to the measured critical steam quality. The conclusions werein line with Hewitt et al. (1965), i.e. that the critical film thickness is insignificantly small. This does not contradict e.g. Ueda & Isayama (1981) since the conditions were not the same, but for the flow conditions and heat fluxes that are typical for BWR operation it was concluded that the critical film thickness is, for practical purposes, zero.
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| 10. |
- Adamsson, Carl, et al.
(författare)
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Modeling and Validation of a Mechanistic Tool (MEFISTO) for the Prediction of Critical Power in BWR Fuel Assemblies
- 2011
-
Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 241:8, s. 2843-2858
-
Tidskriftsartikel (refereegranskat)abstract
- Westinghouse is currently developing the MEFISTO code with the main goal to achieve fast, robust, practical and reliable prediction of steady-state dryout Critical Power in Boiling Water Reactor (BWR) fuel bundle based on a mechanistic approach. A computationally efficient simulation scheme was used to achieve this goal, where the code resolves all relevant field (drop, steam and multi-film) mass balance equations, within the annular flow region, at the sub-channel level while relying on a fast and robust two-phase (liquid/steam) sub-channel solution to provide the cross-flow information. The MEFISTO code can hence provide highly detailed solution of the multi-film flow in BWR fuel bundle while enhancing flexibility and reducing the computer time by an order of magnitude as compared to a standard three-field sub-channel analysis approach. Models for the numerical computation of the one-dimensional field flowrate distributions in an open channel (e.g. a sub-channel), including the numerical treatment of field cross-flows, part-length rods, spacers grids and post-dryout conditions are presented in this paper. The MEFISTO code is then applied to dryout prediction in BWR fuel bundle using VIPRE-W as a fast and robust two-phase sub-channel driver code. The dryout power is numerically predicted by iterating on the bundle power so that the minimum film flowrate in the bundle reaches the dryout criteria. Predicted dryout powers (including trends with flow, pressure, inlet subcooling and power distribution) and predicted dryout locations (both axial and radial) are compared to experimental results, using the entire Westinghouse SVEA-96 Optima3 dryout database, and are shown to yield excellent results.
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| 11. |
- Adamsson, Inger, et al.
(författare)
-
Comparative effects of omeprazole, amoxycillin plus metronidazole versus omeprazole, clarithromycin plus metronidazole on the oral, gastric and intestinal microflora in Helicobacter pylori-infected patients
- 1999
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Ingår i: Journal of Antimicrobial Chemotherapy. - : Nature Publishing Group. - 0305-7453 .- 1460-2091. ; 45, s. A8-A8
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Tidskriftsartikel (refereegranskat)abstract
- Fourteen patients with Helicobacter pylori infection were treated with 20 mg omeprazole, 1 g amoxycillin and 400 mg metronidazole bd for 7 days (OAM), and 16 patients were treated with 20 mg omeprazole, 250 mg clarithromycin and 400 mg metronidazole bd for 7 days (OCM). Saliva, gastric biopsies and faecal samples were collected before, during (day 7) and 4 weeks after treatment in order to analyse alterations of the normal microflora and to determine antimicrobial susceptibility. Both treatment regimens resulted in marked quantitative and qualitative alterations. A selection of resistant streptococcal strains were noticed in both treatment groups, most apparent in the OCM group where a shift from susceptible to resistant strains was recorded. In the OAM group, six patients had overgrowth of resistant Enterobacteriaceae during treatment compared with none in the OCM group, in the gastric microflora. The MICs for Enterococcus spp. and Enterobacteriaceae in faeces increased significantly during treatment in both groups. Nine patients in the OAM group became intestinally colonized by yeasts during treatment. The total anaerobic microflora was strongly suppressed in both treatment groups, although most pronounced in the OCM group, where the frequency of clarithromycin-resistant bacteroides strains increased from 2 to 76% during treatment, and remained at 59% 4 weeks post-treatment. Even if the treatment outcome was better in the OCM group (100%) than in the OAM group (71%), the amoxycillin-based treatment might be preferable from an ecological point of view, since the qualitative alterations in terms of emergence and persistence of resistant strains seemed to be most pronounced in the clarithromycin-treated group.
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| 12. |
- Caraghiaur, Diana, et al.
(författare)
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A model for inertial drop deposition suitable to predict obstacle effect
- 2013
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 260, s. 121-133
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Tidskriftsartikel (refereegranskat)abstract
- The drop deposition increase due to flow obstruction is usually quantified solely by empirical coefficients. In this work we propose a new way to calculate the drop deposition with the capability to predict the obstacle effect. The model is based on the drop volume fraction, slip ratio and turbulence quantities of the continuous phase obtained from the two-fluid calculations. Additional relations are needed to calculate the fluctuating velocities of the drop phase. These relations are based on the fluid integral time scales. A number of relations are tested, which include the effect of drop inertia and drift parameter. The new model is tested in a number of flow combinations, including air-water and helium-water of 1.5 bar and steam-water at 70 bar pressure, for low and high drop concentration. The high concentration flow shows that further studies are needed to include drop size increase due to coalescence and reduction of velocity fluctuation due to drop collisions. The new model is tested for pipe flow containing an obstacle of steam-water flows of 5, 10 and 15 bar pressure. The new model shows the capability to qualify the obstacle effect. Further improvements are needed to increase the quantitative capability.
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| 13. |
- Caraghiaur, Diana, et al.
(författare)
-
Deposition of Inertial Drops in Eulerian Formulation
- 2013
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Ingår i: Proceedings of NURETH-15.
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Konferensbidrag (refereegranskat)abstract
- The drop deposition increase due to flow obstacles is presently quantified by empirical coefficients. To avoid the empiricism, a new deposition model is proposed with the capability to predict the obstacle effect. By the proposed method the deposition is calculated from the local concentration of drops and the normal-to-wall fluctuating velocity. The model shows promising results in predicting the obstacle effect.
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| 14. |
- Caraghiaur, Diana, et al.
(författare)
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Verification of the applicability of random walk models to calculate drop deposition in nuclear fuel assemblies
- 2009
-
Ingår i: Proceedings of the 13th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics.
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Konferensbidrag (refereegranskat)abstract
- The main objective of the paper is to verify the discrete random walk (DRW) and thecontinuous random walk (CRW) Lagrangian Particle Tracking models as a tool to calculatedeposition in nuclear fuel assemblies of Boiling Water Reactors, where the sophisticatedgeometry of the spacer does not permit at present a more computationally expensivealternative. The models have been applied for a wide range of flow conditions and for variousfluids including air-water, steam-water and helium-water flows. In general, the best agreementof predictions with measurements has been obtained for air-water flows. The majordiscrepancy of the models with experimental data has been noted for the high-pressure watervaporflows. Under such conditions the models over-predict the drop deposition rates by anorder of magnitude. It is concluded that the models require further development to beapplicable to BWR conditions. In particular, it is suggested the the drop-wall interactionmodel is improved. The comparison between the two models have shown a betterperformance of CRW model in cases of air-olive oil, air-water and helium-water flows. In case of steam-water at high pressure the behavior of the two models is very different. The major finding of the paper is that a favourable comparison of either model to air-water flowconditions does not prove a good performance at BWR conditions.
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| 15. |
- Holmgren, Jan, 1944, et al.
(författare)
-
Mucosal adjuvants and anti-infection and anti-immunopathology vaccines based on cholera toxin, cholera toxin B subunit and CpG DNA
- 2005
-
Ingår i: Immunology Letters. - : Elsevier. - 0165-2478 .- 1879-0542. ; 97:2, s. 181-8
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Tidskriftsartikel (refereegranskat)abstract
- Mucosal immunisation may be used both to protect the mucosal surfaces against infections and as a means for immunological treatment of peripheral immunopathological disorders through the induction of systemic antigen-specific tolerance ('oral tolerance'). The development of mucosal vaccines, whether for prevention of infectious diseases or for oral tolerance immunotherapy, requires efficient antigen delivery and adjuvant systems that can help to present the appropriate vaccine or immunotherapy antigens to the mucosal immune system. The most potent (but also toxic) mucosal adjuvants are cholera toxin (CT) and the closely related Escherichia coli heat-labile enterotoxin (LT), and much effort and significant progress have been made recently to generate toxicologically acceptable derivatives of these toxins with retained adjuvant activity. Among these are the non-toxic, recombinantly produced cholera toxin B-subunit (CTB). CTB is a specific protective antigen component of a widely registered oral cholera vaccine as well as a promising vector for either giving rise to mucosal anti-infective immunity or for inducing peripheral anti-inflammatory tolerance to chemically or genetically linked foreign antigens administered mucosally. CT and CTB have also recently been used as combined vectors and adjuvants for markedly promoting ex vivo dendritic cell (DC) vaccination with different antigens and also steering the immune response to the in vivo-reinfused DCs towards either broad Th1 + Th2 + CTL immunity (CT) or Th2 or tolerance (CTB). Another type of mucosal adjuvants is represented by bacterial DNA or synthetic oligodeoxynucleotides containing CpG-motifs, which especially when linked to CTB have been found to effectively stimulate both innate and adaptive mucosal immune responses. The properties and clinical potential of these different classes of adjuvants are being discussed. © 2004 Elsevier B.V. All rights reserved.
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| 16. |
- Krejci, Marko, et al.
(författare)
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Development of a model for prediction of annular flow and dryout in BWR fuel assemblies with spacers
- 2005
-
Ingår i: Proceedings of the Eleventh International Topical Meeting on Nuclear Reactor Thermal-Hydraulics.
-
Konferensbidrag (refereegranskat)abstract
- This paper deals with development of a phenomenological annular flow and dryout model for BWR fuel assemblies. The model is based on a solution of conservation equations for mass, momentum and energy for each subchannel in the bundle. Proper closure relations are included to model the inter-subchannel mass, momentum and energy transfer. A fullNewtoniteration scheme is used to solve the algebraic set of finite difference equations. The convergence of the scheme is very robust and it typically takes 5 iterations to find the solution. After finding the flow and enthalpy distribution between all subchannels in a bundle, a newly developed algorithm is applied to calculate the liquid film distribution on channel walls. The algorithm predicts the liquid film flow rate taking into account the local values of the entrainment, deposition and evaporation rates. The spacer influence is taken into account through proper model of intensified deposition rate downstream of spacer locations. The model has been applied for prediction of flow and phase distributions in various fuel assemblies and the results of calculations have been compared to measurements. Good agreement between predictions and measurements has been obtained. The model is also applicable to prediction of dryout occurrence in fuel assemblies, where proper predictions of various effects, e.g. influence of axial power distribution on dryout power, have been obtained.
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| 17. |
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