| 1. |
- Nourgaliev, R. R., et al.
(författare)
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The multiphase Eulerian-Lagrangian transport (MELT-3D) approach for modeling of multiphase mixing in fragmentation processes
- 2003
-
Ingår i: Progress in nuclear energy (New series). - 0149-1970 .- 1878-4224. ; 42:2, s. 123-157
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Tidskriftsartikel (refereegranskat)abstract
- A new numerical approach for modeling of multiphase mixing during melt jet/droplet fragmentation process is developed. Melt or debris movements are simulated by a particle transport model in a Lagrangian formulation, while thermohydraulic conditions of the surrounding medium are obtained from solution of the Navier-Stokes and energy-conservation equations written in an Eulerian formulation. The Lagrangian and the Eulerian solutions are coupled and advanced in time, with source terms included to model the interactions between the particle and the continuum phases. The method is validated against isothermal solid-sphere, and drop fragmentation experiments. It is found that the model is capable of describing the evolution of the melt-coolant multiphase mixing process with reasonable accuracy. The method is then applied to investigate fragmentation of a continuous jet. Effects of variations in jet/coolant velocities, and of coolant thermophysical properties are analyzed, with particular emphasis on their implications for the fragmentation and mixing processes.
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| 2. |
- Theofanous, T. G., et al.
(författare)
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The boiling crisis phenomenon - Part I : nucleation and nucleate boiling heat transfer
- 2002
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Ingår i: Experimental Thermal and Fluid Science. - 0894-1777 .- 1879-2286. ; 26:6-7, s. 775-792
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Tidskriftsartikel (refereegranskat)abstract
- This paper (Part I) and the companion paper (Part II, Exp. Therm. Fluid. Sci. 26 (6-7) (2002) 793- 810) present results of an experimental study on nucleate pool boiling. The experiments were conducted under highly-controlled conditions, using electrically heated, vapor-deposited sub-micron metallic films. A high-speed. high-resolution infrared camera was used to visualize dynamic thermal patterns on the heater's surface over a broad range of heat fluxes, starting from the onset of nucleation and up to boiling crisis. Both fresh heaters and aged heaters were experimented with. The heaters' surface nanomorphology and chemistry were characterized with atomic force microscopy, scanning electron microscopy, and X-ray diffraction spectroscopy. First-of-a-kind experimental data on nucleation and boiling heat transfer at high heat fluxes are presented, and a stark difference between fresh and aged heaters is revealed. Remarkable are the origin, evolution and dynamics of the heater dryout process (leading to burnout), identified quantitatively and captured in action for the first time.
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| 3. |
- Theofanous, T. G., et al.
(författare)
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The boiling crisis phenomenon - Part II : dryout dynamics and burnout
- 2002
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Ingår i: Experimental Thermal and Fluid Science. - 0894-1777 .- 1879-2286. ; 26:6-7, s. 793-810
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Tidskriftsartikel (refereegranskat)abstract
- This is Part II of a two-part paper on the boiling crisis phenomenon. Here we report on burnout experiments conducted on fresh and aged heaters in pool boiling. Critical heat fluxes (CHFs) were found to vary from 50% to 140% of the hydrodynamic limit, previously thought to exist at well-wetting conditions. The burnout events were captured in action (for the first time), using highspeed, high-resolution infrared thermometry. Based on these observations and in conjunction with the levels of CHF reached, we are led to conclude that the phenomenon cannot be (macro)hydrodynamically limited, at east at normal pressure and gravity conditions. Based on infrared thermometry, and aided by X-ray radiography data on void fraction, the case for a scale separation phenomenon in high heat flux pool boiling is argued. This indicates that boiling crisis is controlled by the microhydrodynamics and rupture of an extended liquid microlayer, sitting and vaporizing autonomously on the heater surface. Further. the detailed dynamics of this microlayer, as revealed by our experiments. demonstrates that all previous thermally based models of boiling crisis are inappropriate.
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| 4. |
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| 5. |
- Cadinu, Francesco, et al.
(författare)
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Relating system-to-CFD coupled code analyses to theoretical framework of a multiscale method
- 2008
-
Ingår i: Societe Francaise d'Energie Nucleaire - International Congress on Advances in Nuclear Power Plants - ICAPP 2007, "The Nuclear Renaissance at Work". - 9781604238716 ; , s. 2959-2967
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Konferensbidrag (refereegranskat)abstract
- Over past decades, analyses of transient processes and accidents in a nuclear power plan t have been performed, to a significant extent and with an admirable success, by means of so called system codes, e.g. RELAP5, CATHARE, ATHLET codes. These computer codes, based on a multi-fluid model of two-phase flow, provide an effective, one-dimensional description of the coolant thermal-hydraulics in the reactor system. For some components in the system, wherever needed, the effect of multi-dimensional flow is accounted for through approximate models. The later are derived from scaled experiments conducted for selected accident scenarios. Increasingly, however, we have to deal with newer and ever more complex accident scenarios. In some such cases the system codes fail to serve as simulation vehicle, largely due to its deficient treatment of multi-dimensional flow (in e.g. downcomer, lower plenum). Enter Computational Fluid Dynamics (CFD). Based on solving Navier-Stokes equations, CFD codes have been developed and used, broadly, to perform analysis of multi-dimensional flow, dominantly in non-nuclear industry and for single-phase flow applications. Although not always straightforward, CFD codes can be, and have been, used to analyze thermo-fluid processes in a certain component of the reactor system at a well-defined point during the accident progression. It is natural to think that CFD codes provide the much-needed complementary capability to the system codes. Furthermore, due to the CFD excessive demand on computational resources, ideas were proposed, and attempts were reported in the literature, to use a coupled system-to-CFD code to maximize the benefit of both tools. Easy as it might sound, progress in this area has been sluggish. In this paper, we take a close look at the progress in coupled system-to-CFD code analyses, including coupling algorithms, their implementation and performance. Tackling thermo-fluid dynamics at largely different scales, system codes and CFD codes employ different models and governing equations. This notion led us to the idea to examine the system-to-CFD coupling in the language of multiscale simulations. As a theoretical framework, we bring to bear the heterogeneous multiscale method pioneered by E and Engquist and problem classification offered by E et al.[16]. Viewing system-to-CFD coupling as a multiscale problem, the ultimate objective of the present effort is to define requirements for models and numerical methods, and develop suggestions on a coupling strategy that ensures robust and effective generation and transfer of information between scale-specific simulations (system and CFD).
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| 6. |
- Concilio Hansson, Roberta, et al.
(författare)
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A study of the effect of binary oxide materials in a single droplet vapor explosion
- 2013
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 264, s. 168-175
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Tidskriftsartikel (refereegranskat)abstract
- In an effort to explore fundamental mechanisms that may govern the effect of melt material on vapor explosion's triggering, fine fragmentation and energetics, a series of experiments using a binary-oxide mixture with eutectic and non-eutectic compositions were performed. Interactions of a hot liquid (WO3-CaO) droplet and a volatile liquid (water) were investigated in well-controlled, externally triggered, single-droplet experiments conducted in the Micro-interactions in steam explosion experiments (MISTEE) facility. The tests were visualized by means of a synchronized digital cinematography and continuous X-ray radiography system, called simultaneous high-speed acquisition of X-ray radiography and photography (SHARP). The acquired images followed by further analysis indicate milder interactions for the droplet with non-eutectic melt composition in the tests with low melt superheat, whereas no evident differences between eutectic and non-eutectic melt compositions regarding bubble dynamics, energetics and melt preconditioning was observed in the tests with higher melt superheat.
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| 7. |
- Dinh, Truc-Nam, et al.
(författare)
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Core melt spreading on a reactor containment floor
- 2000
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Ingår i: Progress in nuclear energy (New series). - 0149-1970 .- 1878-4224. ; 36:4, s. 405-468
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Tidskriftsartikel (refereegranskat)abstract
- The ex-vessel core melt spreading, cooling and stabilization is proposed for a nuclear power plant containment design. Clearly, the retention and coolability of the decay-heated core debris is very much the focal point in the proposed new and advanced designs so that, in the postulated event of a severe accident, the containment integrity is maintained and the risk of radioactivity releases is eliminated. The work reported here includes three tasks (i) to review related methodology and data base, (ii) to develop the scaling methodology and (iii) to validate the assessment methodology developed by the authors. The study is based on state-of-the-art knowledge of the melt spreading phenomenology, in particular, and, of severe accident phenomenology in general.
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| 8. |
- Dinh, Truc-Nam
(författare)
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Material property effect in steam explosion energetics : Revisited
- 2007
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Ingår i: Proceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12. - 0894480588 - 9780894480584
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Konferensbidrag (refereegranskat)abstract
- Steam explosion, as a threat to LWR reactor vessel and containment integrity, has been postulated to occur during a hypothetical severe accident with relocation of molten core materials to a water pool either in-vessel or ex-vessel. Studies of molten fuel-coolant interactions (FCI) conducted over the past decades have not resolved the controversy about whether, when, and how melt material properties influence steam explosion energetics. Crucial questions persist about safety significance of experimental evidence about corium low explosivity in various reactor accident scenarios. In this paper, taking into consideration results from recent FCI experiments and analyses, we revisit the study of Dinh et al (1998) and hypotheses proposed therein about mechanisms by which corium physical properties may influence steam explosions. Corium high density, high melting point and low conductivity are found to be central to mechanisms in premixing that govern corium low explosivity. For micro-interactions, three processes, namely drop surface undercooling, nucleation and growth of solid phases, and interfacial instability and breakup are evaluated with respect to their role in fine fragmentation. The paper provides a new hypothesis for rationalizing the effect of corium composition (eutectic vs. non-eutectic) on its triggerability and energetics.
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| 9. |
- Dinh, Truc-Nam
(författare)
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Multiphase flow phenomena of steam generator tube rupture in a lead-cooled reactor system : A scoping analysis
- 2008
-
Ingår i: Societe Francaise d'Energie Nucleaire - International Congress on Advances in Nuclear Power Plants - ICAPP 2007, "The Nuclear Renaissance at Work". - 9781604238716 ; , s. 2765-2775
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Konferensbidrag (refereegranskat)abstract
- The paper is concerned with understanding and quantification of intense multiphase interactions in a Steam Generator Tube Rupture (SGTR) scenario in advanced lead-cooled reactor systems. The scoping approach taken in this paper is to focus on key flow physics that complements other ongoing detailed computational and experimental efforts on SGTG analysis. The present study suggests that (i) the initial pressure shock wave poses no credible threat to invessel structures, except for limited pressure loading on very few adjacent heat-exchange tubes; (ii) the sloshing-relatedfluid motion is well bounded in a domain beyond the heat exchanger; (iii) the pre-mixture is not pre-conditioned for triggering and a postulated steam explosion would have limited energetics; and (iv) an initial discharge of steam/water mass is amenable for entrapment in the primary coolant flow. Implications for further research are discussed in the paper.
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| 10. |
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| 11. |
- Dinh, Truc Nam, et al.
(författare)
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On the numerical simulation of acceleration-driven multi-fluid mixing
- 2006
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Ingår i: Multiphase Science and Technology. - 0276-1459 .- 1943-6181. ; 18:3, s. 199-230
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Tidskriftsartikel (refereegranskat)abstract
- This paper is concerned with computational prediction of acceleration-induced multi-fluid mixing phenomena. Premises and performance of existing approaches are reviewed and analyzed with focus on a late phase behavior. We introduce a new framework whose central idea is to use an interfacial area transport equation (IATE) and a subgrid scale model (SGS) of multi-fluid turbulence to provide a natural transition from DNS-based simulation toward an effective-field model (EFM) and deeply into well-mixed states with continuous refinement of length scale. We present new results and important insights derived from our work on four platform technologies: DNS, EFM, IATE and SGS. We discuss the approach to ensure that developments in different areas effectively emerge and function seamlessly in an overall computational platform for multi-fluid mixing.
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| 12. |
- Dombrovsky, Leonid A., et al.
(författare)
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The effect of thermal radiation on the solidification dynamics of metal oxide melt droplets
- 2008
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 238:6, s. 1421-1429
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Tidskriftsartikel (refereegranskat)abstract
- Cooling and solidification of metal oxide droplets in water are considered, using a single-particle model which takes into account heat conduction and thermal radiation transfer within the particle. It is shown that, for millimeter-size particles, near-infrared absorption of the particle's substance determines the solidification pattern and dynamics. For semi-transparent aluminum oxide particles, the rate of surface solidification is controlled by convective heat transfer. For opaque corium particles, thermal radiation from the particle surface leads to fast surface solidification. The impact of so-formed crust layer on subsequent particle fragmentation is discussed with respect to its influence on steam explosion.
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| 13. |
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| 14. |
- Gong, Shengjie, et al.
(författare)
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An experimental study of rupture dynamics of evaporating liquid films on different heater surfaces
- 2011
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 54:7-8, s. 1538-1547
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data were obtained to reveal the complex dynamics of thin liquid films evaporating on heated horizontal surfaces, including formation and expansion of dry spots that occur after the liquid films decreased below critical thicknesses. The critical thickness of water film evaporating on various material surfaces is measured in the range of 60-150 mu m, increasing with contact angle and heat flux while decreasing with thermal conductivity of the heater material. In the case of hexane evaporating on a titanium surface, the liquid film is found resilient to rupture, but starts oscillating as the averaged film thickness decreases below 15 mu m.
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| 15. |
- Gong, Shengjie, et al.
(författare)
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Diagnostic techniques for the dynamics of a thin liquid film under forced flow and evaporating conditions
- 2010
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Ingår i: MICROFLUID NANOFLUID. - : Springer Science and Business Media LLC. - 1613-4982. ; 9:6, s. 1077-1089
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by quantification of micro-hydrodynamics of a thin liquid film which is present in industrial processes, such as spray cooling, heating (e.g., boiling with the macrolayer and the microlayer), coating, cleaning, and lubrication, we use micro-conductive probes and confocal optical sensors to measure the thickness and dynamic characteristics of a liquid film on a silicon wafer surface with or without heating. The simultaneous measurement on the same liquid film shows that the two techniques are in a good agreement with respect to accuracy, but the optical sensors have a much higher acquisition rate up to 30 kHz which is more suitable for rapid process. The optical sensors are therefore used to measure the instantaneous film thickness in an isothermal flow over a silicon wafer, obtaining the film thickness profile and the interfacial wave. The dynamic thickness of an evaporating film on a horizontal silicon wafer surface is also recorded by the optical sensor for the first time. The results indicate that the critical thickness initiating film instability on the silicon wafer is around 84 mu m at heat flux of similar to 56 kW/m(2). In general, the tests performed show that the confocal optical sensor is capable of measuring liquid film dynamics at various conditions, while the micro-conductive probe can be used to calibrate the optical sensor by simultaneous measurement of a film under quasi-steady state. The micro-experimental methods provide the solid platform for further investigation of the liquid film dynamics affected by physicochemical properties of the liquid and surfaces as well as thermal-hydraulic conditions.
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| 16. |
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| 17. |
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| 18. |
- Gong, Shengjie, et al.
(författare)
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Simulation and validation of the dynamics of liquid films evaporating on horizontal heater surfaces
- 2012
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 48, s. 486-494
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Tidskriftsartikel (refereegranskat)abstract
- In this study a non-linear governing equation based on lubrication theory is employed to model the thinning process of an evaporating liquid film and ultimately predict the critical thickness of the film rupture under impacts of various forces resulting from mass loss, surface tension, gravity, vapor recoil and thermo-capillary. It is found that the thinning process in the experiment is well reproduced by the simulation. The film rupture is caught by the simulation as well, but it underestimates the measured critical thickness at the film rupture. The reason may be that the water wettability of the heater surfaces is not taken into account in the model. Thus, the minimum free energy criterion is used to obtain a correlation which combines the contact angle (reflection of wettability) with the critical thickness from the simulation. The critical thicknesses predicted by the correlation have a good agreement with the experimental data (the maximum deviation is less than 10%).
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| 19. |
- Hansson Concilio, Roberta, et al.
(författare)
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Dynamics and preconditioning in a single drop vapor explosion
- 2007
-
Ingår i: Proceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12. - 0894480588 - 9780894480584
-
Konferensbidrag (refereegranskat)abstract
- In order to develop a mechanistic understanding of the thermal-hydraulic processes in vapor explosion, it is paramount to characterize the dynamics of the hot liquid (melt) drop fragmentation and the volatile liquid (coolant) vaporization. In the present study, these intricate phenomena are investigated by performing well-controlled, externally triggered, single-drop experiments, employing a high-speed digital visualization system with synchronized cinematography and X-ray radiography system called SHARP (Simultaneous High-speed Acquisition of X-ray Radiography and Photography). The processed images, after an elaborate image processing, revealed the internal structure and dynamic evolution of the hot liquid fragmentation and related vaporization of the coolant. Such data gives way to new insights into the physics of the vapor explosion phenomena and quantification of the associated dynamic micro interactions. Analysis of the experimental results shows that, followed an external perturbation (trigger), a high temperature molten material (tin) drop underwent deformation and partial fragmentation already during the first cycle of bubble growth. Analysis of the SHARP data reveals correlation between the drop's dynamics in the first bubble cycle and energetics of the subsequent explosive evaporation in the second cycle. This finding provides a basis to suggest a so-called melt drop preconditioning i.e. deformation/ pre-fragmentation of a hot melt drop immediately following the pressure trigger, being instrumental to the subsequent coolant entrainment and resulting energetics of the so-triggered drop explosion.
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| 20. |
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| 21. |
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| 22. |
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| 23. |
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| 24. |
- Hansson, Roberta Concilio
(författare)
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An experimental study on the dynamics of melt-water micro-interactions in a Vapor explosion
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vapor explosion as a result of Molten Fuel-Coolant Interactions (MFCI) postulated to occur in certain severe accident scenarios in a nuclear power plant presents a credible challenge on the plant containment integrity. Over the past several decades, a large body of literature has been accumulated on vapor explosion phenomenology and methods for assessment of the related risk. Vapor explosion is driven by a rapid fragmentation of high-temperature melt droplets, leading to a substantial increase of heat transfer areas and subsequent explosive evaporation of the volatile coolant. Constrained by the liquid-phase coolant, such rapid vapor production in the interaction zone causes pressurization and dynamic loading on surrounding structures. While such a general understanding has been established, the triggering mechanism and subsequent dynamic fine fragmentation have yet not been clearly understood. A few mechanistic fragmentation models have been proposed, however, computational efforts to simulate such phenomena generated a large scatter of results. In order to develop a mechanistic understanding of thermal-hydraulic processes in vapor explosion, it is paramount to characterize dynamics of fragmentation of the hot liquid (melt) drop and vaporization of the volatile liquid (coolant). In the present study, these intricate phenomena are investigated by performing well-controlled, externally triggered, single-drop experiments, using advanced diagnostic techniques to attain visual information of the processes. The methodology’s main challenge stemming from the opaqueness of the molten material surrounded by the vapor film and rapid dynamics of the process, was overcome by employing a high-speed digital visualization system with synchronized cinematography and X-ray radiography system called SHARP (Simultaneous High-speed Acquisition of X-ray Radiography and Photography). The developed image processing methodology, focus on a separate quantification of vapor and molten material dynamics and an image synchronization procedure, consists of a series steps to reduce the effect of uneven illumination and noise inherited of our system, further segmentation, i.e. edge detection, and extraction of image features, e.g. area, aspect ratio, image center and image intensity (radiography). Furthermore, the intrinsic property of x-ray radiation, namely the differences in linear mass attenuation coefficients over the beam path through a multi-component system, which translates the image intensity to a transient projection of the molten material morphology, was exploited. A methodology for the quantitative analysis of the x-ray images, i.e. transient maps of the fragmented melt, was developed. Its uncertainties were evaluated analytically and experimentally pointing towards the need to minimize the X-ray scattering and noise inherited from the optical system, for a more accurate quantification and a larger calibrated thickness range. Analysis of the data obtained by the SHARP system and image processing procedure developed provided new insights into the physics of the vapor explosion phenomena, as well as, quantitative information of the associated dynamic micro-interactions. The qualitative analysis, based on the matched radiograph and photographic images, describe the bubble and melt interrelated progression granting information on the phenomenological micro-interaction of the vapor explosion process. The dynamics of the initially disturbed vapor film is composed by multiple cycles, where the vapor bubble grows to a maximum diameter and collapses. X-ray radiographs show that during the first bubble expansion, the melt undergoes deformation/pre-fragmentation but does not follow the bubble interface during the subsequent expansion; suggesting no mixing between coolant and melt. Coolant entrainment occurs when the expanded bubble collapses leading to fine fragmentation of the molten material due to explosive evaporation. The vapor bubble expansion, fed by these fragments at the boundary, reaches its critical size, and start collapsing. The remaining melt is accountable for the following cycle. Bubble dynamics analysis shows a strong correlation between energetics of the subsequent explosive evaporation and the high temperature molten material drop (tin) deformation/partial fragmentation during the first bubble growth. The data suggest that this pre-fragmentation may have been responsible in providing an adequate mixing condition that promotes coolant entrainment during the bubble collapse stage. The SHARP observations followed by further analysis leads to a hypothesis about a novel phenomenon called pre-conditioning, according to which dynamics of the first bubble-dynamics cycle and the ability of the melt drop to deform/pre-fragment dictate the subsequent explosivity of the so-triggered drop.
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| 25. |
- Hansson, Roberta Concilio, et al.
(författare)
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Dynamics and preconditioning in a single-droplet vapor explosion
- 2009
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 167:1, s. 223-234
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Tidskriftsartikel (refereegranskat)abstract
- The present study aims to develop a mechanistic understanding of the thermal-hydraulic processes in a vapor explosion, which may occur in nuclear power plants during a hypothetical severe accident, involving interactions of high-temperature corium melt and volatile coolant. Dynamics of the hot liquid (melt) droplet and the volatile liquid (coolant) were investigated in the Micro-Interactions in Steam Explosion Experiments (MISTEE) facility by performing well-controlled, externally triggered, single-droplet experiments, using a high-speed visualization system with synchronized digital cinematography and continuous X-ray radiography, called Simultaneous High-speed Acquisition of X-ray Radiography and Photography (SHARP). After an elaborate image processing, the SHARP images depict the evolution of both melt material (dispersal) and coolant (bubble dynamics) and their microscale interactions. The analysis of the data shows a deficiency in using the bubble dynamics alone to provide a consistent explanation of the energetic behavior. In contrast, the SHARP data reveal a correlation between the droplet's dynamics in the bubble's first cycle and the energetics of the subsequent explosive evaporation in the bubble's second cycle. The finding provides a basis to suggest that a so-called melt-droplet preconditioning, i.e., deformation/prefragmentation of a hot melt droplet immediately following the pressure trigger, is instrumental to the subsequent coolant entrainment, evaporation, and energetics of the resulting vapor explosion.
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| 26. |
- Hansson, Roberta Concilio, et al.
(författare)
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Simultaneous high speed digital cinematographic and X-ray radiographic imaging of a intense multi-fluid interaction with rapid phase changes
- 2009
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 33:4, s. 754-763
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Tidskriftsartikel (refereegranskat)abstract
- As typical for the study of the vapor explosions, the qualitative and quantitative understanding of the phenomena requires visualization of both material and interface dynamics. A new approach to multifluid multiphase visualization is presented with the focus on the development of a synchronized highspeed visualization by digital cinematography and X-ray radiography. The developed system, named SHARP (simultaneous high-speed acquisition of X-ray radiography and photography), and its image processing methodology, directed to an image synchronization procedure and a separate quantification of vapor and molten material dynamics, is presented in this paper. Furthermore, we exploit an intrinsic property of the X-ray radiation, namely the differences in linear mass attenuation coefficients over the beam path through a multi-component system, to characterize the evolution of molten material distribution. Analysis of the data obtained by the SHARP system and image processing procedure developed granted new insights into the physics of the vapor explosion phenomena, as well as, quantitative information of the associated dynamic micro-interactions.
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| 27. |
- Haraldsson, H. O., et al.
(författare)
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Effect of solidification on drop fragmentation in liquid-liquid media
- 2001
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Ingår i: Heat and Mass Transfer. - : Springer Science and Business Media LLC. - 0947-7411 .- 1432-1181. ; 37:4-5, s. 417-426
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents results of experimental and analytical investigation on molten alloy drop fragmentation in water pool. Emphasis is directed towards delineating the roles which melt to coolant heat transfer and melt solidification play in the fragmentation process. The strong impact of coolant temperature upon fragmentation process is addressed. A set of 23 drop fragmentation experiments were performed, in which 8 experiments employed a low melting point alloy, cerrobend-70 and 15 experiments using Pb-Bi eutectic alloy as drop fluid. The results show strong impact of coolant temperature on particle size distribution of the fragmented drops. A linear stability analysis of the interface between the two liquid fluids with thin crust growing between them, is performed. A modified dimensionless Aeroelastic number, for Kelvin-Helmholtz instability, is obtained and used as a criteria for fragmentation of molten drops penetrating into another liquid coolant media with lower temperature. The nondimensionalized mean diameter of the fragmented particles is correlated with the Aeroelastic number.
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| 28. |
- Journeau, C., et al.
(författare)
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European Research on the Corium issues within the SARNET network of excellence
- 2008
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Ingår i: International Conference on Advances in Nuclear Power Plants, ICAPP 2008. - 9781605607870 ; , s. 1172-1181
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Konferensbidrag (refereegranskat)abstract
- Within SARNET, the corium topic covers all the behaviors of corium from early phase of core degradation to in or ex-vessel corium recovery with the exception of corium interaction with water, direct containment heating and fission product release. The corium topic regroups in three work packages the critical mass of competence required to improve significantly the corium behavior knowledge. The spirit of the SARNET networking is to share the knowledge, the facilities and the simulation tools for severe accidents, so to reach a better efficiency and to rationalize the R&D effort at European level. Extensive benchmarking has been launched in most of the areas of research. These benchmarks were mainly dedicated to the recalculation of experiments, while, in the next periods, a larger focus will be given to integral experiments or reactor applications. Eventually, all the knowledge will be accumulated in the ASTEC severe accident simulation code through physical model improvements and extension of validation database. This paper summarizes the progress that has been achieved in the frame of the networking activities. A special focus is placed on the melt pool and debris coolability and corium-concrete interaction, in which, the effects due to multidimensional geometries and heterogeneities has been shown, during SARNET, to play a crucial role and for which further research is still needed.
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| 29. |
- Karbojian, Aram, et al.
(författare)
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A scoping study of debris bed formation in the DEFOR test facility
- 2009
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 239:9, s. 1653-1659
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Tidskriftsartikel (refereegranskat)abstract
- Motivated to understand the processes which govern the formation and characteristics of a debris bed and hence its coolability during a postulated severe accident of a light water reactor, a new research program called DEFOR (DEbris FORmation) was initiated at the Royal Institute of Technology (KTH). This paper presents results obtained in scoping experiments conducted during an initial phase of the DEFOR program. The DEFOR-E test campaign is concerned with the DEFOR test facility commissioning and exploratory study of phenomena occurred during a debris bed formation. Binary oxide mixtures at different superheat temperatures were used as the corium melt simulants. The scoping experiments revealed the effect of water pool depth and subcooling, melt mass and material properties on the debris bed characteristics. Insights gained from the DEFOR-E test campaign help guide the scaling, design and operation of the subsequent experiments in the DEFOR program.
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| 30. |
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| 31. |
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| 32. |
- Kozlowski, Tomasz, et al.
(författare)
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Evaluation of coupled codes RELAP5/PARCS capability for BWR global stability prediction
- 2007
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Ingår i: Proceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12. - 9780894480584 - 0894480588 ; , s. 1619-1640
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Konferensbidrag (refereegranskat)abstract
- The present study is concerned with 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 safety significance of a number of stability transients which trigger core instability and challenge reactor protection systems. The technical approach adopted is 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 BWR stability.
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| 33. |
- 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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| 34. |
- Kubarev, Andrej, et al.
(författare)
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Design of BWR instability suppression system
- 2008
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Ingår i: International Conference on the Physics of Reactors 2008, PHYSOR 08. - 9781617821219 ; , s. 2062-2068
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Konferensbidrag (refereegranskat)abstract
- This paper explores the concept of instability suppression system and its performance in a BWR plant. The key idea adopted from the work of Aleksakov et al. (1980) is to utilize information provided by the in-core power monitoring detectors to guide movement of control rods in a way that suppress the global, regional and local instability. In the paper, effectiveness of a simplified suppression algorithm is characterized by implementing it on a real BWR model, using the RELAP5/PARCS coupled thermal-hydraulics and neutron kinetics code. Both forced power oscillations and realistic reactor transients (feedwater temperature transients, control rod drop) were analyzed. The results suggest that, without requiring any modifications for the in-reactor diagnostics and equipment, the proposed suppression system is capable of significantly mitigating the impact of core instability events on plant performance by maintaining the core parameters within the safe operational range.
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| 35. |
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| 36. |
- Kudinov, Pavel, et al.
(författare)
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An experimental study on debris formation with corium simulant materials
- 2008
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Ingår i: International Conference on Advances in Nuclear Power Plants, ICAPP 2008. - 9781605607870 ; , s. 1191-1199
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Konferensbidrag (refereegranskat)abstract
- Characteristics of corium debris beds formed in a severe coremelt accident are studied in DEFOR-S experiments, in which binary-oxidic simulant-material melts are discharged into a water pool. Water subcooling and pool depth are found to significantly influence the fragment morphology and agglomeration. The DEFOR-S data to date are indicative of the effect of melt composition, notably eutectic vs. non-eutectic. Synthesis of the DEFOR-S observations with respect to debris fragment's shape and surface roughness suggest the governing role of competitive mechanism: drop breakup, freezing and solid fracture.
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| 37. |
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| 38. |
- Kudinov, Pavel, et al.
(författare)
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Molten Oxidic Particle Fracture during Quenching in Water
- 2010
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Ingår i: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings. ; , s. P2.32-
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Konferensbidrag (refereegranskat)abstract
- Present work is motivated by the observations of debris particles morphology obtained as a result of quenching of high temperature molten oxidic jet in a subcooled water pool. Insights gained from the Debris Bed Formation (DEFOR) experiments (Kudinov et al., 2010) paved way to suggestions that melt fragmentation and the resulting particle morphology are largely influenced by (i) melt droplet instability and breakup; (ii) melt cooling and solidification; (iii) cavity formation; and (iv) solid particle fracture. Analysis of the DEFOR results suggests that there is a strong influence of water subcooling on the debris morphology. Particles are round-shape if subcooling of water is less than 50°C, and, at subcooling higher than 80°C, most of the particles are fractured rock-like with sharp edges. In present work we are considering the following hypothesis which can explain an apparent strong influence of moderate changes in temperature of water on morphology of the debris particle: rapid increase of heat flux during transition from film to nucleate boiling can cause solid particle fracture due to thermal stress. To verify the hypothesis we perform transient heat transfer and thermo-elastic stress analysis for a melt droplet instantaneously immersed into water coolant. We are also examining competition between hydrodynamic fragmentation and freezing at transient boiling heat transfer to identify conditions at which characteristic time scales are competitive. In the paper we demonstrate that rapid change in transient boiling heat flux (which is highly sensitive to water subcooling) can cause fracture of the particle. As well there is an effect of competition between freezing and hydrodynamic fragmentation at high subcooling of water. By parametric study we develop a “map” of the debris morphology. The map defines whether or not the particle will be fractured taking into account intrinsic uncertainty in the transition boiling characteristics and particle material properties. The map appears to be in a good agreement with the experimental observations.
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| 39. |
- Kudinov, Pavel, et al.
(författare)
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THE DEFOR-S EXPERIMENTAL STUDY OF DEBRIS FORMATION WITH CORIUM SIMULANT MATERIALS
- 2010
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 170:1, s. 219-230
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Tidskriftsartikel (refereegranskat)abstract
- Characteristics of corium debris beds formed in a severe core melt accident are studied in the Debris Bed Formation-Snapshot (DEFOR-S) test campaign, in which superheated binary-oxidic melts (both eutectic and non-eutectic compositions) as the corium simulants are discharged into a water pool. Water subcooling and pool depth are found to significantly influence the debris fragments' morphology and agglomeration. When particle agglomeration is absent, the tests produced debris beds with porosity of similar to 60 to 70%. This porosity is significantly higher than the similar to 40% porosity broadly used in contemporary analysis of corium debris coolability in light water reactor severe accidents. The impact of debris formation on corium coolability is further complicated by debris fragments' sharp edges, roughened surfaces, and cavities that are partially or fully encapsulated within the debris fragments. These observations are made consistently in both the DEFOR-S experiments and other tests with prototypic and simulant corium melts. Synthesis of the debris fragments from the DEFOR-S tests conducted under different melt and coolant conditions reveal trends in particle size, particle sphericity, surface roughness, sharp edges, and internal porosity as functions of water subcooling and melt composition. Qualitative analysis and discussion reaffirm the complex interplay between contributing processes (droplet interfacial instability and breakup, droplet cooling and solidification, cavity formation and solid fracture) on particle morphology and, consequently, on the characteristics of the debris beds.
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| 40. |
- Ma, Weimin, et al.
(författare)
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A study on effects of debris bed prototypicality on coolability
- 2007
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Ingår i: Proceedings of the 12<sup>th</sup> International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH12). - 0894480588 - 9780894480584
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Konferensbidrag (refereegranskat)abstract
- This paper is concerned with the modeling and prediction of the coolability of debris beds formed in a hypothetical core-melt accident in a light water reactor (LWR). The focus is placed on analysis of the potential effects of the prototypical configuration and characteristics of the debris beds on its coolability, namely (i) porosity range, (ii) multi-dimensionality, (iii) inhomogeneity, (iv) particle morphology, and (v) heat generation (e.g. volumetric heating vs. local heaters). The analysis results indicate availability of substantial coolability margins compared to previous assessments based on models and experiments using an idealized bed (e.g. ID homogenous debris layer). Notably, the high porosity (up to 70%) of debris beds, obtained in experiments and expected to be the case of prototypical debris beds, could dramatically increase the dryout heat flux by 100% and more, depending on particle size, compared with the dryout heat flux predicted for debris beds with traditionally assumed porosity of approximately 40%. Bed inhomogeneity represented by micro channels in a mini bed is predicted to enhance the dryout heat flux by up to ∼50%, even if the micro channels occupies only a small fraction (e.g., less than 4% of the bed). The effect of coolant side ingress into a multidimensional bed is predicted to enhance the dryout heat flux by more than 40%.
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| 41. |
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| 42. |
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| 43. |
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| 44. |
- Ma, Weimin, et al.
(författare)
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The effects of debris bed's prototypical characteristics on corium coolability in a LWR severe accident
- 2010
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 240:3, s. 598-608
-
Tidskriftsartikel (refereegranskat)abstract
- This paper is concerned with coolability assessment of a debris bed formed in fuel coolant interactions (FCIs) during a hypothetical severe accident in a light water reactor (LWR). The focus is placed the potential effect of the bed's prototypical characteristics on its coolability, in terms of (i) porosity range, (ii) multi-dimensionality, (iii) inhomogeneity, (iv) particle morphology, and (v) heat generation method (e.g. volumetric heating vs. local heaters). The analysis results indicate availability of substantial coolability margins compared to previous assessments based on models and experiments using an idealized bed configuration (e.g. 1 D homogenous debris layer). Notably, high porosity (up to 70%) of debris beds, obtained in experiments and expected to be the case of prototypical debris beds, could increase the dryout heat flux by 100% and more, depending on particle size, compared with the dryout heat flux predicted for debris beds with traditionally assumed porosity of approximately 40%. Bed inhomogeneity represented by micro-channels in a mini bed is predicted to enhance the dryout heat flux by up to similar to 50%, even if the micro-channels occupy only a small volume fraction (e.g., less than 4%) of the bed. The effect of coolant side ingress into a multidimensional bed is predicted to enhance the dryout heat flux by up to 40% for the beds analyzed.
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| 45. |
- Ma, Weimin, et al.
(författare)
-
Thermal-hydraulic performance of heavy liquid metal in straight-tube and U-tube heat exchangers
- 2009
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 239:7, s. 1323-1330
-
Tidskriftsartikel (refereegranskat)abstract
- Motivated by an increased interest in heavy liquid metal (lead or lead alloy) cooled fast reactors (LFR) and accelerator-driven system (ADS), the present paper presents a study on resistance characteristics and heat transfer performance of liquid lead bismuth eutectic (LBE) flow through a straight-tube heat exchanger and a U-tube heat exchanger. The investigation is performed on the TALL test facility at KTH. The heat exchangers have counter-current flow arrangement, and are made from a pair of 1-m-long concentric ducts, with the LBE flowing in the inner tube of 10mm I.D. and the secondary coolant flowing in the annulus. The inlet temperature of LBE into the heat exchangers is from 200 degrees C to 450 degrees C with temperature drops from 0 degrees C to 100 degrees C within the LBE flow range of Re = 10(4)-10(5). Analysis of the experimental results obtained provides a basic understanding and quantification of the regimes of lead-bismuth flow and heat transfer through a straight tube and a U-shaped tube. The unique data base also serves as benchmark and improvement for system thermal-hydraulic codes (e.g. RELAP, TRAC/AAA) whose development and testing were dominantly driven by applications in water-cooled systems. Lessons and insights learnt from the study and recommendations for the heat exchanger selection are discussed.
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| 46. |
- Ma, Weimin, et al.
(författare)
-
Thermal-hydraulic performance of lead-bismuth eutectic in a straight-tube and a u-tube heat exchangers
- 2007
-
Ingår i: Proceedings of the 12th International Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-12). - 0894480588 - 9780894480584
-
Konferensbidrag (refereegranskat)abstract
- Motivated by an increased interest in lead alloy cooled Fast Reactors (LFR) and Accelerator Driven System (ADS), the present paper presents a study on resistance characteristics and heat transfer performance of molten lead bismuth eutectic (LBE) flow through a straight tube heat exchanger and a U-tube heat exchanger. The investigation is performed on the TALL test facility at KTH. The heat exchangers have counter-current flow arrangement, and are made from a pair of 1-meter-long concentric ducts, with the LBE flowing in the inner tube of 10mm ID and the secondary coolant flowing in the annulus. The inlet temperature of LBE into the heat exchangers is from 200°C to 450°C with temperature drops from 0°C to 100°C within the LBE flow range of Re=10 4-105. Analysis of the experimental results obtained provides a basic understanding and quantification of the regimes of lead-bismuth flow and heat transfer through a straight tube and a U-shaped tube. The unique data base also serves as benchmark and improvement for system thermal-hydraulic codes (e.g. RELAP, TRAC/AAA) whose development and testing were dominantly driven by applications in water-cooled systems. Lessons and insights learnt from the study and recommendations for the heat exchanger selection are discussed.
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| 47. |
- Nourgaliev, R. R., et al.
(författare)
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A pseudocompressibility method for the numerical simulation of incompressible multifluid flows
- 2004
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322 .- 1879-3533. ; 30:7-8, s. 901-937
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an explicit characteristics-based, conservative, finite-difference method for the simulation of incompressible multiphase flows. The method is based on the artificial compressibility concept, e,,tended to variable-density, and uses a time stretching procedure to relieve the acoustic constrain. We take advantage of the algorithmic simplicity and hyperbolicity provided by the artificial compressibility to develop a flow solver that is numerically robust, accurate and effective for massively parallel computations of incompressible multifluid flows. The resulting method, named Numerical Acoustic Relaxation or NAR, is a combination of the AC concept with the Level Set method for interface-capturing and the Ghost-Fluid method to compute flows with multiple, arbitrary density variation, free or stationary interfaces. In this paper we demonstrate convergence and accuracy of the solver by computing such standard test problems as the Lid-Driven Cavity and Doubly Periodic Shear Layer. Competitiveness with approximate projection, vorticity stream function, pseudospectral, and Lattice Boltzmann Equation is also discussed. In addition, we demonstrate the interface-capturing features of NAR by means of the simple Rayleigh-Taylor and Water Column Collapse problems.
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| 48. |
- Nourgaliev, R. R., et al.
(författare)
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Adaptive characteristics-based matching for compressible multifluid dynamics
- 2006
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Ingår i: Journal of Computational Physics. - : Elsevier BV. - 0021-9991 .- 1090-2716. ; 213:2, s. 500-529
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an evolutionary step in sharp capturing of shocked, high acoustic impedance mismatch (AIM) interfaces in an adaptive mesh refinement (AMR) environment. The central theme which guides the present development addresses the need to optimize between the algorithmic complexities in advanced front capturing and front tracking methods developed recently for high AIM interfaces with the simplicity requirements imposed by the AMR multi-level dynamic solutions implementation. The paper shows that we have achieved this objective by means of relaxing the strict conservative treatment of AMR prolongation/restriction operators in the interfacial region and by using a natural-neighbor-interpolation (NNI) algorithm to eliminate the need for ghost cell extrapolation into the other fluid in a characteristics-based matching (CBM) scheme. The later is based on a two-fluid Riemann solver, which brings the accuracy and robustness of front-tracking approach into the fast local level set front-capturing implementation of the CBM method. A broad set of test problems (including shocked multi-gaseous media, bubble collapse, underwater explosion and shock passing over a liquid drop suspended in a gaseous medium) was performed and the results demonstrate that the fundamental assumptions/approximations made in modifying the AMR prolongation/restriction operators and in using the NNI algorithm for interfacial treatment are acceptable from the accuracy point of view, while they enable an effective implementation and utility of the structured AMR technology for solving complex multiphase problems in a highly compressible setting.
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| 49. |
- Nourgaliev, R. R., et al.
(författare)
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On lattice Boltzmann modeling of phase transition in an isothermal non-ideal fluid
- 2002
-
Ingår i: Nuclear Engineering and Design. - 0029-5493 .- 1872-759X. ; 211:2-3, s. 153-171
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Tidskriftsartikel (refereegranskat)abstract
- A new lattice Bolztmann BGK model for isothermal non-ideal fluid is introduced and formulated for an arbitrary lattice, composed of several D-dimensional sublattices. The model is a generalization of the free-energy-based lattice Bolztmann BGK model developed by Swift et al. (1996). We decompose the equilibrium distribution function in the BGK collision operator into ideal and non-ideal parts and employ second-order Chapman-Enskog expansion for treatment of both parts. Expansion coefficients for the non-ideal part are, in general. functions of macroscopic variables, designed to reproduce desired pressure tensor (thermodynamic aspects) and to eliminate the aphysical artifacts in the lattice Bolztmann model. The new model is shown to significantly improve quality of lattice Boltzmann modeling of interfacial phenomena. In the present model. the interface spurious velocity is orders of magnitude lower than that for existing LBE models of non-ideal fluids. A new numerical scheme for treatment of advection and collision operators is proposed to significantly extend stability limits, in comparison to existing solution methods of the 'master' lattice Bolztmann equation. Implementation of a 'multifractional stepping' procedure for advection operator allows to eliminate severe restriction CFL = 1 in traditionally used 'stream-and-collide' scheme. An implicit trapezoidal discretization of the collision operator is shown to enable excellent performance of the present model in stiff high-surface-tension regime. The proposed numerical scheme is second order accurate. both in time and space.
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| 50. |
- Nourgaliev, R. R., et al.
(författare)
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Shock wave refraction patterns at interfaces
- 2005
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322 .- 1879-3533. ; 31:9, s. 969-995
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Tidskriftsartikel (refereegranskat)abstract
- Interactions of shock waves with gas-gas and gas-liquid interfaces (under both slow-fast and fast-slow configurations) are studied using the recently developed Adaptive Characteristics-based Matching (aCBM) method for capturing interfaces in compressible multi-fluid media. First, we verify our approach for the gas-gas case; a class of problems for which a substantial body of knowledge already exists. Then, we consider slow-fast, gas-liquid interfaces under weak shocks, and fast-slow, liquid-gas interfaces under strong shocks. The very high acoustic impedance mismatch situation here creates significant numerical (simulation) and experimental (visualization) difficulties, and the literature for it is meager and sporadic. Compared to gas-gas interfaces we note both similarities and differences. We discuss the sources for these differences, as well as potential implications of generalizing and embedding such results in multi-dimensional simulation schemes towards improving their front-capturing performance.
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