| 1. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 2. |
- Deng, Yucheng, et al.
(författare)
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A numerical study on the levitation system for droplet preparation in a fuel-coolant interaction experiment
- 2023
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Ingår i: Progress in nuclear energy (New series). - : Elsevier BV. - 0149-1970 .- 1878-4224. ; 159
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Tidskriftsartikel (refereegranskat)abstract
- The MISTEE facility at KTH was designed to investigate the process and phenomena of a molten droplet falling into a water pool that may be encountered in fuel-coolant interactions (FCI) during a severe accident of light water reactors. An aerodynamic levitation mechanism is proposed to hold the molten droplet during its preparation (melting and heating up to a prescribed temperature) in an induction furnace. The crucible is flushed with argon through an injection nozzle at the bottom to prevent the droplet from falling out of the crucible. A numerical simulation of the aerodynamic levitation system is performed in the present study with the objective of determining and optimizing the design. The problem was simplified as an isothermal two-phase flow in an axisymmetric geometry. The simulation is realized through ANSYS Fluent v17 platform, which employs the VOF method to track interfaces between two phases and the SST k-omega model to describe turbulence flow of argon gas. The numerical model is validated against tests performed in the MISTEE facility after mesh sensitivity study. It is then applied to investigate the impacts of various parameters on the facility levitation capability and the droplet stability. According to the simulation results, stable molten droplets can be obtained in the designed experimental setup. The simulation also provides the appropriate values of argon inlet velocity and sample mass at which a stable droplet can be obtained inside the crucible before its discharge. Either higher or lower inlet velocity will destabilize the formation of the droplet. Considering the temperature-dependent melt properties, both surface tension and viscosity affect the movement and deformation of the molten droplet. The wettability of melt on the crucible wall is critical to droplet formation, and it is found that a poor wettability can ensure the levitation of droplet.
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| 3. |
- Deng, Yucheng, et al.
(författare)
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An experimental study on droplet quench and steam explosion in boric acid solutions
- 2023
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Ingår i: Progress in nuclear energy (New series). - : Elsevier BV. - 0149-1970 .- 1878-4224. ; 166
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Tidskriftsartikel (refereegranskat)abstract
- Boric acid (H3BO3) is widely adopted as an additive in the coolant of light water reactors for reactivity control, but its effect on fuel coolant interactions (FCI) during severe accidents (especially on steam explosion) was rarely investigated. To examine the effect of the boric acid additive in coolant on steam explosion, a series of molten droplet-coolant interaction tests using H3BO3 solutions (with concentration ranging from 0-3.2% by weight) is carried out in the present study. The characteristics of melt-coolant interactions are the occurrence probability of typical phenomena (no fragmentation, minor fragmentation, or spontaneous steam explosion), lateral deformation ratio, quench depth, pressure impulse and debris particle size distribution. The statistical data of such characteristics are obtained through repeating 20 runs of the same test category. The experimental results show that the H3BO3 addition in coolant has various impacts on the above-mentioned characteristics of melt-coolant interactions, depending on the H3BO3 concentration. In particular, the probability of steam explosion sightly decreases as the H3BO3 concentration increases from zero to 1.2 wt.%, but significantly increases as the H3BO3 concentration further increases to 3.2 wt.% trough 2.2 wt.%. Namely, the inhibiting effect of boric acid on steam explosion is diminishing with increasing H3BO3 concentration beyond 1.2 wt.%. It is also found that both melt and coolant temperatures are crucial parameters impacting the likelihood and energetics of steam explosion.
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| 4. |
- Deng, Yucheng
(författare)
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An Experimental Study on Steam Explosion of Multiple Droplets in Different Chemical Solutions
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Considering the severity of possible steam explosion in severe accidents of light water reactors (LWRs), a series of tests were carried out in the MISTEE facility at KTH to investigate steam explosion characteristics as multiple molten droplets of tin were falling through coolant pools containing deionized water, boric acid solution, boric-acid-sodium-phosphate neutral solution and seawater, separately. The experimental results revealed distinct and complex characteristics of steam explosion of multiple droplets, which were not observed in previous single-droplet steam explosion experiments. The tin melt samples of 5 g and 20 g were employed to formulate different numbers of multiple droplets. In the tests with 5g melt samples, the steam explosion of multiple droplets was more energetic at a deeper explosion location - a similar trend was found in the single-droplet steam explosion tests with 1 g melt. However, the tests of 20 g samples did not show a clear trend in a wide range of explosion depth. The peak pressure and impulse increased with the increasing mass of the melted sample. The steam explosion occurred more closely to the coolant pool surfaces in the seawater and chemical solutions than in deionized water. Steam explosion intensity was significantly reduced in a neutral solution containing 1.2 wt.% boric acid and sodium phosphate. The influence of the chemical solutions on steam explosion was diminishing in the tests with multiple droplets.
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| 5. |
- Deng, Yucheng, et al.
(författare)
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An Experimental study on steam explosion of multiple droplets in different chemical solutions
- 2024
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 226
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the interest in steam explosion in chemical solutions and seawater, a series of tests were carried out in the MISTEE facility at KTH to investigate steam explosion characteristics as multiple molten droplets of tin were falling through a coolant pool containing deionized water, boric acid solution, neutral solution of boric acid and sodium phosphate, and seawater, separately. The experimental results revealed distinct and complex characteristics of steam explosion of multiple droplets, which were not observed in previous single-droplet steam explosion experiments. The tin melt samples of 5 g and 20 g were employed to formulate different numbers of multiple droplets. In the test with 5 g melt, steam explosion was more energetic at a deeper explosion location − a similar trend found in the single-droplet steam explosion test with 1 g melt. However, the test of 20 g melt did not show a clear trend in a wide range of explosion depth. The peak pressure and impulse increased with increasing mass of melt sample. The steam explosion occurred more closely to the coolant pool surfaces in the seawater and chemical solutions than in deionized water. Steam explosion intensity was significantly reduced in a neutral solution containing 1.2 wt.% boric acid and sodium phosphate. The influence of the chemical solutions on steam explosion was diminishing in the tests with multiple droplets.
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| 6. |
- Deng, Yucheng, et al.
(författare)
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An experimental study on the effect of chemical additives in coolant on steam explosion
- 2024
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier Ltd. - 0017-9310 .- 1879-2189. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- In assessment of severe accident risk in light water reactors (LWRs), steam explosion is a nonnegligible phenomenon following a relocation of core melt (corium) into coolant, and thus various research efforts have been paid to steam explosion. There had been numerous studies showing that the occurrence of steam explosions is influenced by several factors such as melt and coolant temperatures, melt materials, non-condensable gasses, etc. However, most of the existing experiments used deionized (DI) water or tap water as coolant, with little consideration of the effect of chemicals (e.g. boric acid, sodium hydroxide, sodium phosphate) commonly applied in reactor coolant. To examine the effect of the chemical additives in coolant on steam explosion, the present study performs a series of molten Tin droplet-coolant interaction tests using DI water and different chemical solutions, including H3BO3 solutions, NaOH + H3BO3 neutral solutions, and Na3PO4 + H3BO3 neutral solutions. The experimental results show that adding NaOH and Na3PO4 in boric acid solution significantly affects the occurrence probability of spontaneous steam explosion, because of the presence of PO43− and H+ ions. When different solutions have equivalent concentrations of H3BO3, the peak pressure values of the spontaneous steam explosion of Sn droplets are similar among various solutions. Compared with those in DI water, steam explosion in the chemical solutions occurs predominantly within a narrow range of depth from 28 mm to 40 mm and produces a much higher peak pressure. This implies that more energetic steam explosions may occur in the chemical solutions.
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| 7. |
- Deng, Yucheng
(författare)
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An Experimental Study on the Effect of Coolant Salinity on Steam Explosion
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The steam explosion plays an essential role in the safety analysis of light water reactors (LWRs). Some studies have demonstrated that the occurrence of steam explosions is dependent on many factors such as melt and coolant temperatures, melt and coolant properties, non-condensable gases, etc. After the Fukushima accident, seawater as an emergency coolant and its impact on fuel coolant interactions are receiving attention. However, there is still little knowledge of the impact of seawater on steam explosions. The present study is intended to examine the effect of coolant salinity on steam explosion through a series of tests with single molten droplet falling in different coolant pools (DI water, and seawater at different salinities from 7.7 g/kg to 35 g/kg). The experimental results reveal that the salinity of coolant significantly influences the probability of spontaneous steam explosion of molten tin droplets. The probability of steam explosion generally increases with increasing salinity from 0 to 17.5 g/kg. The molten droplet in seawater experiences more pronounced deformation at the same depth before the vapor film of the droplet collapses. What’s more, the peak pressure generated by the steam explosion in seawater is notably higher than that in DI water. The fragmentation of molten tin droplets after the explosion is enhanced accordingly.
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| 8. |
- Deng, Yucheng, et al.
(författare)
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An experimental study on the effect of coolant salinity on steam explosion
- 2024
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 201
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Tidskriftsartikel (refereegranskat)abstract
- The steam explosion plays an essential role in the safety analysis of light water reactors (LWRs). Some studies have demonstrated that the occurrence of steam explosions is dependent on many factors such as melt and coolant temperatures, melt and coolant properties, non -condensable gases, etc. After the Fukushima accident, seawater as an emergency coolant and its impact on fuel coolant interactions are receiving attention. However, there is still little knowledge on the impact of seawater on steam explosion. The present study is intended to examine the effect of coolant salinity on steam explosion through a series of tests with single molten droplet falling in different coolant pools (DI water, and seawater at different salinities from 7.7 g/kg to 35 g/kg). The experimental results reveal that the salinity of coolant significantly influences the probability of spontaneous steam explosion of molten tin droplets. The probability of steam explosion generally increases with increasing salinity from 0 to 17.5 g/kg. The molten droplet in seawater experiences more pronounced deformation at same depth before the vapor film of the droplet collapses. What's more, the peak pressure generated by steam explosion in seawater is notably higher than that in DI water. The fragmentation of molten tin droplet after the explosion is enhanced accordingly.
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| 9. |
- Deng, Yucheng, 1993-
(författare)
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Experimental Study on Steam Explosions in Chemical Solutions and Seawater
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Steam explosions may be encountered in severe accidents of light water reactors (LWRs), which are thermal detonations caused by rapid and intense vaporization of the coolant upon its direct contact with the core melt (corium). Motivated by the interest in understanding and mitigation of severe accident progression, many studies have been conducted to investigate the steam explosion phenomena during severe accidents. However, most of the previous studies did not consider the effect of chemical additives in the coolant of nuclear power plants, such as additions of H3BO3, NaOH and Na3PO4 for water chemistry control, and direct utilization of seawater (NaCl additive) under an extreme condition like the Fukushima accident. The present thesis work is motivated to fill the knowledge gap concerning the impacts of chemical additives (H3BO3, NaOH, Na3PO4, and NaCl) on steam explosions. The primary objective of the present research is to obtain characteristics of steam explosions in seawater and chemical solutions of H3BO3/NaOH/Na3PO4 with prototypical concentrations. To achieve this goal, a series of experiments have been carried out in the MISTEE experimental platform at KTH, involving single droplet and multiple droplets falling into a variety of coolant pool filled with seawater or chemical solutions of H3BO3/NaOH/Na3PO4 additives. The thesis work consists of four parts as follows.The first part is a description of the experimental methodology developed in the present study. Two experimental facilities, dubbed MISTEE-CE and MISTEE-SEA of respective mechanical plug and aerodynamic levitation for melt delivery, were designed on the MISTEE platform. Both setups were equipped with high-speed cameras for visualization, a pressure sensor for dynamic pressure measurement, and a fragment catcher for debris collection. A double-crucible design was employed to enable induction heating while avoiding melt contamination. The aerodynamic levitation system was implemented in MISTEE-SEA to reduce the disturbance of the mechanical plug. All chemical solutions were prepared in the laboratory with degassed deionized water. Tin (Sn) was chosen as the melt material due to benign properties suitable for safe handling in the laboratory.The second part is the presentation of visual observations and parameters selected to characterize steam explosions. The visualization includes the phenomena of droplet-coolant interactions and steam explosion occurrences. A molten single droplet falling into the coolant pool with deionized water or chemical solution might experience one of the three typical phenomena: deformation without fragmentation, minor fragmentation, or spontaneous steam explosion. In contrast, a multi-droplet test might involve merging and multiple explosions of droplets, resulting in a more complex set of phenomena. The quench depth and the lateral deformation ratio were defined and used to analyze the dynamic process of a single droplet in the coolant, while the peak pressure was employed to compare steam explosion energetics. In addition, the size distribution of debris particles was scrutinized.The third part is a summary and highlights of the experimental study on single-droplet steam explosion in different chemical solutions, using 1g of melt sample. The results revealed that the H3BO3 additive had little impact on steam explosion when the H3BO3 concentration was lower than 1.2 wt.%, but the risk of steam explosion in 3.2 wt.% H3BO3 solution was higher. The addition of NaOH and Na3PO4 to an H3BO3 solution significantly offset the influence on steam explosion. This suggests that the presence of PO43- and H+ ions play a significant role in spontaneous steam explosions. Additionally, seawater enhanced the occurrence of spontaneous steam explosions, with a clear correlation between increasing salinity and a higher likelihood of steam explosion. Compared to deionized water, chemical solutions (including seawater) caused more pronounced deformation in molten droplets at equivalent depths prior to direct contact of melt with coolant. Furthermore, the peak pressures of steam explosions in chemical solutions had the potential to reach notably higher values than those in deionized water. The chemical solutions except for the one of 1.2 wt.% H3BO3 tended to produce higher fractions of finer debris particles. The fourth part is about the experimental results of an investigation on steam explosion involving multiple droplets falling into deionized water and chemical solutions, using 5 g and 20 g of melt samples, respectively. It was found that under identical test conditions, the peak pressure of steam explosion increased with melt sample mass, resulting in a noticeably higher fraction of fine debris particles in the case of 20 g melt sample. The steam explosion location was concentrated within a shallower range when using chemical solutions instead of deionized water. In contrast to single-droplet experiments, the influence of the chemical solutions on the steam explosion was diminishing in the tests with multiple droplets.
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| 10. |
- Fang, Di, et al.
(författare)
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A numerical study of liquid film dynamics in multi-nozzle spray cooling of downward-facing surface
- 2023
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322 .- 1879-3533. ; 161
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Tidskriftsartikel (refereegranskat)abstract
- In a consideration of spray cooling as the potential cooling mechanism for the in-vessel melt retention (IVR) strategy of nuclear reactors because of its superior heat removal efficiency, the SPAYCOR experiment has been conducted at KTH to investigate the spray cooling capacity of multiple nozzles applied to a downward-facing heated surface. In the present study, the dynamics of liquid film on the downward-facing surface resulting from the multi-nozzle spray are numerically simulated by using a coupled Eulerian-Lagrangian method implemented in the OpenFOAM platform. Prior to simulation of the SPAYCOR experiment, the numerical approach is used to calculate two theoretical setups which have known analytical solutions, with the objective to validate the models in predicting liquid film dynamics either in spray or on an inclined surface. In the simulation of the SPAYCOR experiment, the predicted film morphology shows a good agreement with the experimental observation. What's more, the influential factors, including the inclination of the downward-facing heater surface, the nozzle-to-surface distance as well as the nozzle-array layout, are also investigated numerically in the present study. The simulation results show that a decreasing nozzle-to-surface distance does not only lead to a thicker liquid film and a lower velocity in the vicinity of each spray coverage, but also increases non-uniformity of the liquid film. The nozzles-array layout has little influence on the average liquid film thickness and velocity, but significantly affects the film morphology.
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| 11. |
- Fang, Di, et al.
(författare)
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A numerical study on multi-nozzle spray cooling of downward-facing heater surface
- 2024
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Ingår i: Progress in nuclear energy (New series). - : Elsevier BV. - 0149-1970 .- 1878-4224. ; 173
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study on multi-nozzle spray cooling of a downward-facing heater surface has been carried out in the SPAYCOR facility at KTH, to provide data assessing the feasibility of spray cooling for in-vessel melt retention (IVR) in light water reactors. To help understand the characteristics and influential factors of the liquid film formed on the heater surface in spray, a numerical study on the dynamics of an isothermal liquid film on the heater surface has also been performed by adopting the OpenFOAM platform, and Eulerian and Lagrangian methods for liquid film and droplets, respectively. The present study is an extension of the previous modeling from hydrodynamics to thermal-hydraulics of the spray cooling problem, via adding heat flux of the heater and two convective heat transfer models between the heater wall and the liquid film. Moreover, droplets-film interaction model is modified. The SPAYCOR experiment is simulated by the numerical models, and the simulation results show a good agreement between the numerical and experimental data, in particular when the modified droplets-film interaction model is applied. After the validation of the numerical models against the SPAYCOR experiment, the numerical models are employed to investigate influential factors on heat transfer, such as mass flux, nozzle-to-surface distance, and nozzle matrix layout. The results indicate that heat transfer is enhanced by increasing mass flux and decreasing nozzle-to-surface distance, and the change of nozzle matrix from inline to staggered layout has little impact on heat removal capacity or temperature distribution of the multi-nozzle spray cooling.
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| 12. |
- Fu, Le, et al.
(författare)
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Structural integrity and damage of glass-ceramics after He ion irradiation : Insights from ZrO2-SiO2 nanocrystalline glass-ceramics
- 2023
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Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 43:6, s. 2624-2633
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Tidskriftsartikel (refereegranskat)abstract
- Developing new radiation-resistant materials and understanding the structural damages caused by radiation are persistent goals of material scientists. Here, we report on the structural integrity and damage to ZrO2-SiO2 nanocrystalline glass-ceramics after radiation with 1.4 MeV He ions at three different fluences: 1.0 x 1016 ions/ cm2 (low), 5.0 x 1016 ions/cm2 (moderate), and 1.0 x 1017 ions/cm2 (high) at 500 degrees C. Grazing incident X-ray diffraction shows the tetragonal-ZrO2 to monoclinic-ZrO2 phase transformation induced by microstrain from the irradiation. The addition of yttrium indicated tetragonal-ZrO2 stabilization effect during irradiation. The irra-diated glass-ceramics show a Raman signal-enhancement effect probably related to the electronic structure changes of the amorphous SiO2 component in the glass-ceramics. The formation of microcracks and lattice de-fects within ZrO2 nanocrystallites is the main structural damage caused by irradiation. There was no observable amorphization of ZrO2 nanocrystallites due to irradiation. No obvious He bubbles were detected, either. The formation of microcracks results in a decrease of in the nanohardness of the glass-ceramics. The results provide fundamental experimental data to understand the structural integrity and damage caused by radiation, which could be useful to design radiation-resistant nanocrystalline glass-ceramics for extremely radioactive environments.
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| 13. |
- Guo, Qiang, et al.
(författare)
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An experimental study on quenching of metallic spheres in seawater
- 2023
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 148
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by quenching of melt droplets and debris particles in seawater during a hypothetical severe accident of light water reactors (LWRs), the quenching process of stainless-steel spheres in a seawater pool was investigated in the present study. The polished spheres were pre-heated up to 1000celcius in an induction furnace with inserted atmosphere, and then immersed into the subcooled water pool in a chamber made of transparent quartz. A thermocouple was embedded in the center of the sphere to measure the history of the sphere's temperature, while a high-speed camera was employed to record the quenching process and vapor film dynamics. Quantitative data, e.g. film thickness and oscillation, of the vapor film evolution during the quenching process were obtained through an image processing program developed on the MATLAB platform.The experimental results indicated that the quenching rate was higher in seawater than in deionized water, and the vapor film collapsed at a temperature higher than the Leidenfrost temperature in deionized water. The trend appeared more significant with increasing subcooling of water. The comparison of the quenched spheres suggested the surface of the sphere in seawater achieved higher degree of discoloration and roughening than that in deionized water, probably due to the additives of salt which change water properties. The image processing and analysis revealed that the vapor film had different thickness profile along the upper and lower hemispheres, and the averaged film thickness was smaller in seawater than in de-ionized water during the stage of stable film boiling. The vapor film was thinning and oscillating with time, and its fluctuations appeared different frequencies and amplitudes at the upper and lower locations, which may explain the mechanism of the earlier collapse of vapor film in the quenching process of a high-temperature sphere in seawater.
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| 14. |
- Guo, Qiang, et al.
(författare)
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Oxidation of molten zirconium-containing droplet in water
- 2024
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Ingår i: Progress in nuclear energy (New series). - : Elsevier BV. - 0149-1970 .- 1878-4224. ; 175
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Tidskriftsartikel (refereegranskat)abstract
- During a severe accident in light water reactors, the molten reactor core (corium) falls into a water pool in the form of a jet. Complex interactions may occur between the melt and coolant known as molten fuel-coolant interactions (FCI), including energetic coolant evaporation and metallic melt (e.g., Zr and Fe) oxidation. This may further lead to steam and hydrogen explosions, which are both substantial safety risks for nuclear power plants. The heat of reaction and hydrogen production during oxidation can influence the progress and severity of the accidents. For example, the reaction heat may prolong the liquid state of corium, potentially leading to highintensity explosions, whereas the generated hydrogen can create a combustible atmosphere, increasing the risk of hydrogen explosion. Therefore, this study evaluates the hydrogen production and oxidation degree of molten metallic droplets falling into a water pool to improve the FCI models for the risk evaluation of severe accident safety. The MISTEE-OX facility at KTH, which has been primarily built to study steam explosions is modified to investigate oxidation during FCI and provide experimental data on the oxidation behaviour of metallic droplets (Zr/Fe) quenched in a subcooled water pool. The dynamics of the falling droplets and generated bubbles are recorded using a high-speed camera, and the total volume of the bubbles is measured using a graduated cylinder. This study presents preliminary experimental results of the oxidation between Zr/Fe droplets and water, as well as recent improvements in measurement methods and facility upgrades. Our research findings are useful to enhance the knowledge of the oxidation process in FCI phenomena and validate the related mechanistic models in FCI codes.
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| 15. |
- Xiang, Yan, et al.
(författare)
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A numerical study on melt jet breakup in a water pool using coupled VOF and level set method
- 2024
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Ingår i: Nuclear Engineering and Design. - : Elsevier Ltd. - 0029-5493 .- 1872-759X. ; 426
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Tidskriftsartikel (refereegranskat)abstract
- During severe core meltdown accidents of a light water reactor (LWR), the core melt (molten corium) may fall into a water pool, resulting in molten fuel coolant interactions (FCI). Quantitative understanding of FCI phenomena is paramount to corium risk assessment of LWRs such as Nordic boiling water reactors which employ reactor cavity flooding as severe accident management strategy (SAMS). Melt jet breakup and droplet fragmentation play an important role in FCI, affecting debris coolability and steam explosion energetics which are considered in ex-vessel corium risk assessment. The present study is concerned with numerical simulation of melt jet breakup in a water pool using a multiphase computational fluid dynamics (MCFD) approach where a coupled Level Set and Volume of Fluid (CLSVOF) method is used to capture melt-coolant interfaces. The focus is placed on the prediction of interface instabilities and jet breakup length, and their influential factors (melt materials, jet diameter, fall height, in-pool structures, multiple jets and pitch/diameter ratio). The simulation results are compared with the data of the DEFOR-M tests carried out at KTH. There is a good agreement between simulation and experiment, in terms of jet deformation pattern and jet breakup length. It is also found that the jet breakup length is different from the values predicted by well-known correlations (e.g., Taylor's, Epstein Fauske's and Matsuo's). Based on the experimental and numerical data, a new correlation for the jet breakup length is developed in the similar formula of the Satio's correlation.
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| 16. |
- Xiang, Yan, et al.
(författare)
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An experimental investigation on debris bed formation from fuel coolant interactions of metallic and oxidic melts
- 2023
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 233
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Tidskriftsartikel (refereegranskat)abstract
- During postulated severe accidents in a light water reactor (LWR), the core melt (corium) may relocate to the lower head and fail the reactor pressure vessel (RPV). The corium is expected to undergo fuel coolant interactions (FCI) if the reactor cavity is flooded with water. Both FCI energetics and resulting debris bed coolability are of paramount importance to reactor safety, since the ex-vessel corium poses a threat to the containment integrity if steam explosion occurs or the debris bed is uncoolable, leading to release of radioactive fission products to the environment. The present study is intended to quantify the characteristics of a debris bed resulting from FCI, which are crucial to debris bed coolability. Different from the previous studies with only oxidic materials, various materials, including metallic ones of Sn, Sn-Bi and Zn as well as oxidic one of Bi2O3-WO3, were employed as the simulants of corium (mixture of UO2/ZrO2/Zr/Fe) in the present study to investigate the effects of melt materials, melt superheat and coolant subcooling on debris bed formation in a water pool. High-speed photography was applied to visualize melt jet breakup, droplets fragmentation, as well as fragments sedimentation on the pool floor. Other obtained data are debris bed shape (profile) and porosity, as well as morphology and size distri-bution of debris particles. The comparative results of various tests provided insights toward filling the knowledge gap on debris bed characteristics under different melt materials and compositions.
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| 17. |
- Xiang, Yan, et al.
(författare)
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Experimental investigation on debris bed formation from metallic melt coolant interactions
- 2023
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Ingår i: International journal of thermal sciences. - : Elsevier BV. - 1290-0729 .- 1778-4166. ; 192, s. 108398-
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by risk quantification of severe core meltdown accidents which may occur light water reactors, an extensive DEFOR (DEbris FORmation) test series with various molten oxidic materials was conducted previously at Royal Institute of Technology to investigate the characteristics of debris beds formed from oxidic melt-water interactions, which are important to the coolability of debris beds and thus the retention of core melt. Yet, little attention has been paid to metallic melt which exist in the core melt. The present study is intended to fill in the knowledge gap, i.e., to characterize metallic melt-water interactions when a melt jet falls into a deep water pool. Nine DEFOR-M tests are carried out to clarify the effects of melt jet diameter, free fall height and water pool depth on metallic debris formation characteristics. Molten tin of 20 kg is employed as the simulant of metallic melt. A melt sensor and a mass sensor are installed to detect the discharging period of coherent jet and the mass accumulation of debris bed, respectively. A high-speed camera is applied to record the process of jet breakup, debris fragmentation and solidification, and debris bed formation. The experimental results show that the water pool depth has a significant influence on steam explosion and debris bed formation characteristics. Moreover, the jet breakup length is sensitive to jet diameter and free fall height. Finally, the features of metallic debris beds are compared with those of oxidic ones in respects of debris bed's configuration and porosity, particles' morphology and size distribution.
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| 18. |
- Xiang, Yan, et al.
(författare)
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Experimental investigation on ex-vessel debris bed formation using low melting-point melt of binary metals
- 2023
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Ingår i: Progress in nuclear energy (New series). - : Elsevier BV. - 0149-1970 .- 1878-4224. ; 157
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Tidskriftsartikel (refereegranskat)abstract
- During severe accidents in a light water reactor, the core melt (corium) may relocate to the lower head and fail the reactor pressure vessel (RPV). The corium will be ejected to the reactor cavity upon the RPV failure and undergo melt coolant interactions (FCI) if the cavity is flooded with water. The FCI process does not only de-termines the characteristics of the resulting debris bed which are important to coolability, but also induces a steam explosion risk which may threaten containment integrity. The present study is concerned with charac-terization of debris bed formed from FCI of metal-rich corium failing into a deep water pool in the reactor cavity. Low melting-point metals Tin and Tin-Bismuth (20 kg) were employed as the simulant materials of metal-rich corium melt. Ten tests were carried out on the DEFOR-M test facility at KTH to investigate the effects of various parameters on debris bed formation, such as melt superheat, coolant subcooling, material. The melt jet fragmentation and fragments movement in the water pool as well as debris deposition on the pool floor were recorded by high-speed cameras. Melt sensors and weight sensors were installed to detect the period of melt jet discharge and the mass of forming debris bed. The porosity of debris bed was obtained through the debris bed volume measured by a three-dimensional laser scanner and the pore volume measured by water absorption. The final configuration of debris bed was also reconstructed through the laser scanner data, and the debris particles were sieved for their size distribution. The experimental results revealed the FCI phenomena and debris bed characteristics including configuration and porosity of debris bed as well as morphology and size distribution of debris particles under different melt superheats, coolant subcooling, materials.
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| 19. |
- XiaoTeng, Ma, et al.
(författare)
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Transient heat transfer analysis in packed beds : Entropy generation model and multi-objective optimization
- 2019
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Ingår i: SCIENCE CHINA-TECHNOLOGICAL SCIENCES. - : SCIENCE PRESS. - 1674-7321 .- 1869-1900. ; 62:11, s. 1999-2008
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Tidskriftsartikel (refereegranskat)abstract
- Due to the important role of the unsteady heat transfer process of packed beds in industrial production, the construction of the transient heat transfer model is of great significance for the operation and optimization. The present study performs a transient thermal analysis of packed bed, in which the convective heat transfer and conductive thermal resistance within the particles are considered simultaneously. A mathematical model is established of the total entropy generations (0-t) contributed by viscous dissipation and heat transfer; the influence of particle diameter, air flow rate, and pressure drop, is then investigated. Because of the time cost, these results present some different trends from the steady-state process. Furthermore, for a laboratory heat transfer system, with the aid of the genetic algorithm we adopt a multi-objective genetic algorithm model and modified expressions of the entropy generations are set as objective functions. Finally, optimal operational and structural parameters are obtained for different fan power settings. When the fan power is 300 W, the optimal particle diameter and inlet wind speed are 14 mm and 2.4 m/s, respectively. The results also suggest that the time cost is reduced with increasing fan power consumption.
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