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Dryout and Power Distribution Effects in Boiling Water Reactors
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , x, 42 p.
Series
Trita-FYS, ISSN 0280-316X ; 2009:59
Keyword [en]
Dryout, Film flow analysis, Power distribution, Measurements, Subchannel
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-11343ISBN: 978-91-7415-481-8 (print)OAI: oai:DiVA.org:kth-11343DiVA: diva2:274304
Public defence
2009-11-13, Sal FR4, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100618Available from: 2009-10-28 Created: 2009-10-28 Last updated: 2010-07-19Bibliographically approved
List of papers
1. Measurements of the Liquid Film Flow Rate in High Pressure Annular Flow with Various Axial Power Distributions
Open this publication in new window or tab >>Measurements of the Liquid Film Flow Rate in High Pressure Annular Flow with Various Axial Power Distributions
2005 (English)In: HEAT 2005, Gdansk, Poland, June 26–30, 2005, 2005Conference paper, Published paper (Refereed)
Abstract [en]

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.

Keyword
Film flow analysis, Measurements
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13426 (URN)
Note
QC 20100618Available from: 2010-06-18 Created: 2010-06-18 Last updated: 2010-11-08Bibliographically approved
2. Eperimental Investigation of the Liquid Film for Annular Flow in a Tube with Various Axial Power Distributions
Open this publication in new window or tab >>Eperimental Investigation of the Liquid Film for Annular Flow in a Tube with Various Axial Power Distributions
2005 (English)In: NURETH 11, Avignon, France, October 2–6, 2005, 2005Conference paper, Published paper (Refereed)
Abstract [en]

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.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13428 (URN)
Note
QC 20100618Available from: 2010-06-18 Created: 2010-06-18 Last updated: 2010-11-08Bibliographically approved
3. Film flow measurements for high-pressure diabatic annular flow in tubes with various axial power distributions
Open this publication in new window or tab >>Film flow measurements for high-pressure diabatic annular flow in tubes with various axial power distributions
2006 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 236, no 23, 2485-2493 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Axial power distributions, Film flow measurements, Mass flow
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13430 (URN)10.1016/j.nucengdes.2006.03.002 (DOI)000241899800007 ()2-s2.0-33749614541 (Scopus ID)
Note
QC 20100618Available from: 2010-06-18 Created: 2010-06-18 Last updated: 2017-12-12Bibliographically approved
4. Modeling and Validation of a Mechanistic Tool (MEFISTO) for the Prediction of Critical Power in BWR Fuel Assemblies
Open this publication in new window or tab >>Modeling and Validation of a Mechanistic Tool (MEFISTO) for the Prediction of Critical Power in BWR Fuel Assemblies
2011 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 241, no 8, 2843-2858 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13431 (URN)10.1016/j.nucengdes.2011.01.033 (DOI)000294374600026 ()
Note
QC 20120327. Updated from submitted to published.Available from: 2010-06-18 Created: 2010-06-18 Last updated: 2017-12-12Bibliographically approved
5. Influence of Axial Power Distribution on Dryout: Film-Flow Models and Experiments
Open this publication in new window or tab >>Influence of Axial Power Distribution on Dryout: Film-Flow Models and Experiments
2010 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 240, no 6, 1495-1505 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
CRITICAL HEAT-FLUX; PREDICTION; CHANNELS; CODE; CHF
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13447 (URN)10.1016/j.nucengdes.2010.02.013 (DOI)000278442200022 ()2-s2.0-77950926658 (Scopus ID)
Note
QC 20100618Available from: 2010-06-18 Created: 2010-06-18 Last updated: 2017-12-12Bibliographically approved

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