| 1. |
- Nourgaliev, R. R., et al.
(författare)
-
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
-
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.
|
|
| 2. |
- Theofanous, T. G., et al.
(författare)
-
The boiling crisis phenomenon - Part I : nucleation and nucleate boiling heat transfer
- 2002
-
Ingår i: Experimental Thermal and Fluid Science. - 0894-1777 .- 1879-2286. ; 26:6-7, s. 775-792
-
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.
|
|
| 3. |
- Theofanous, T. G., et al.
(författare)
-
The boiling crisis phenomenon - Part II : dryout dynamics and burnout
- 2002
-
Ingår i: Experimental Thermal and Fluid Science. - 0894-1777 .- 1879-2286. ; 26:6-7, s. 793-810
-
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.
|
|
| 4. |
|
|
| 5. |
- Cadinu, Francesco, et al.
(författare)
-
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
-
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).
|
|
| 6. |
- Concilio Hansson, Roberta, et al.
(författare)
-
A study of the effect of binary oxide materials in a single droplet vapor explosion
- 2013
-
Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 264, s. 168-175
-
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.
|
|
| 7. |
- Dinh, Truc-Nam, et al.
(författare)
-
Core melt spreading on a reactor containment floor
- 2000
-
Ingår i: Progress in nuclear energy (New series). - 0149-1970 .- 1878-4224. ; 36:4, s. 405-468
-
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.
|
|
| 8. |
- Dinh, Truc-Nam
(författare)
-
Material property effect in steam explosion energetics : Revisited
- 2007
-
Ingår i: Proceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12. - 0894480588 - 9780894480584
-
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.
|
|
| 9. |
- Dinh, Truc-Nam
(författare)
-
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
-
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.
|
|
| 10. |
|
|
