| 1. |
- Zeng, Xiao, et al.
(författare)
-
A scoping study on remelting process of a debris bed in the lower head of reactor pressure vessel
- 2023
-
Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 189
-
Tidskriftsartikel (refereegranskat)abstract
- Coolability and retention of core melt (corium) in the lower head of reactor pressure vessel (RPV) has been accepted as a severe accident management strategy to maintain the reactor pressure vessel (RPV) integrity of a light water reactor. To qualify the in-vessel melt retention strategy, lots of studies have been performed to investigate the natural convection heat transfer of a melt pool in the lower head. However, little work has been attributed to the precursory phase of the melt pool, i.e., the remelting process of a debris bed which is formed in the lower head at the very beginning of corium relocation from the core the lower head. The present study is motivated to conduct an experimental study on the debris remelting process. For this purpose, a dedicated test facility named COREM (COrium REMelting) is conceived and constructed, which features internal heating of electromagnetic induction and visualization of debris remelting dynamics. The test section is a semicircular vessel representing a slice of scaled-down RPV lower head, whose front and back walls are made of transparent tempered glass which facilitate visualization and induction heating of the debris bed. Fiber probes with multiple optical temperature sensors are mounted in the semicircular wall of the test section to measure its temperature distribution. In the scoping test, n-octanol and Wood's metal are selected as the simulant materials of metallic and oxidic components of corium, respectively, and their particles ware loaded in the test section to form a debris bed. This paper presents the first two scoping tests which have been performed with the COREM facility so far, under different mixing ratios of two debris materials. The measured data include the photography of debris remelting processes and the temperatures in the debris bed and the semicircular wall. Based on the temperature distributions, heat flux profile along the semicircular vessel wall is also estimated. The scoping tests well reproduce the dynamic process of debris remelting, with two distinct stages of fusion of n-octanol and Wood's metal, i.e., melting successively from low to high melting-point debris particles. During the remelting process, the vessel wall temperatures increase with the polar angle firstly and then decrease gradually, leading to the highest temperature appearing in the middle of the lower layer of the stratified molten pool which is finally formed.
|
|
| 2. |
- Li, Huixiong, et al.
(författare)
-
蒸汽-冷流体接触冷凝流动的数值模拟
- 2005
-
Ingår i: Gongcheng Rewuli Xuebao. - Beijing, China. - 0253-231X. ; 26, s. 963-966
-
Tidskriftsartikel (refereegranskat)abstract
- 介绍了关于蒸汽-冷流体直接接触冷凝流动与传热的数值计算模型与部分研究结果。用Level Set方法确定蒸汽-冷流体接触界面的位置和形状,建立了对蒸汽和冷流体普遍适用的动量、能量和质量守恒方程,在能量和质量寺恒方程中增加了部分项用于计算蒸汽冷凝所产生的影响。用有限差分法在交错网格上离散控制方程,用Runge-Kutta法-五阶WENO组合格式求解Level Set输运方程,用压力修正的迭代Projection方法求解动量方程,而用SIMPLE方法求解温度控制方程。对算例的计算结果表明,本文所建立的数值计算模型能反映物理现象的宏观特性。根据计算结果,分析了本文模型的优缺点,并指出了今后改进的方向。
|
|
| 3. |
|
|
| 4. |
- Li, Liangxing, et al.
(författare)
-
Dynamic characteristics of molten droplets and hot particles falling in liquid pool
- 2010
-
Ingår i: Frontiers of Energy and Power Engineering in China. - : Springer Science and Business Media LLC. - 1673-7393 .- 1673-7504. ; 4:2, s. 246-251
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamic characteristics of molten droplets and hot particles at the very beginning of their fall into coolant pools are presented. The falling course of a single droplet or a single hot particle was recorded by a high-speed camera and a curve of velocity vs. time was obtained. Emphasis was placed on the effects of the droplet's size and temperature, the coolant's temperature and properties, and the droplet's physical properties on the moving behavior. The results for the all cases showed that the velocity of a falling droplet/particle decreased rapidly but rebounded shortly, at the beginning of droplet/particle falling in the coolant. Following such a V-shaped evolution in velocity, the droplet/particle slows down gradually to a comparatively steady velocity. An increase in either coolant temperature or droplet temperature results in a larger velocity variation in the "J-region", but a smaller deceleration when it moves out of the "J-region". The elevated volatility of a coolant leads to a steeper deceleration in the "J-region" and beyond. The bigger size of a particle leads to a greater velocity variation in the "J-region" and terminal velocity. A high melting point and thermal conductivity as well as lower heat capacity contribute to dramatic variation in the "J-region" and low terminal velocity.
|
|
| 5. |
- Li, Liangxing, et al.
(författare)
-
Evaluation of the void fraction in the crescent-shape moderator cell of the CARR-CNS
- 2008
-
Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 403:12, s. 2036-2042
-
Tidskriftsartikel (refereegranskat)abstract
- The mathematical model developed in a previous paper is improved in the present paper for analyzing and evaluating the void fraction profiles in the crescent-shape moderator cell of the Cold Neutron Source (CNS) of the China Advanced Research Reactor (CARR) which is now under construction in the China Institute of Atomic Energy (CIAE). The model is then applied to the case of the CARR-CNS with liquid hydrogen as a moderator and the void fraction in the crescent-shape moderator cell of the CARR-CNS is evaluated. The calculation results show that the void fraction in the crescent-shape moderator cell less than 20%. The model and the calculation results will help to obtain insight of the mechanism that controls the void fraction distribution in the crescent-shape moderator cell, and provide theoretical supports for the moderator cell construction.
|
|
| 6. |
- Li, Liangxing, et al.
(författare)
-
Experimental investigation on the moving characteristics of molten metal droplets impacting coolant
- 2008
-
Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 32:4, s. 962-972
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports the results of an experimental investigation on the moving characteristics of molten metal droplets impacting coolant free surface. A visualization experimental facility of molten fuel coolant interactions (MFCI) is designed and set up in the present study. The lead–bismuth (Pb–Bi) alloys are employed as the metal materials. An automatic control circuit is designed and applied to control the release of the molten droplets. High-speed camera is employed to record the movement of the molten metal droplets falling down and into a coolant pool. Based on the analysis of the experimental data, a so-called “J-region” of the droplet’s velocity–time curves was found and the melt droplet enters the “J-region” when it impacts the free water surface. In the “J-region”, the velocity of the melt droplet decreases rapidly and suddenly at first, and then increases again. The droplet gradually reaches a comparatively steady velocity when it leaves the “J-region”. The present study provides essential information for further study on the fragmentation behavior of high-temperature molten droplets in coolant.
|
|
| 7. |
- Li, Liangxing, et al.
(författare)
-
Study on void fraction distribution in the moderator cell of Cold Neutron Source systems in China Advanced Research Reactor
- 2007
-
Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 393:1-2, s. 336-346
-
Tidskriftsartikel (refereegranskat)abstract
- A physical model is developed for analyzing and evaluating the void fraction profiles in the moderator cell of the Cold Neutron Source (CNS) of the China Advanced Research Reactor (CARR), which is now constructing in the China Institute of Atomic Energy (CIAE). The results derived from the model are compared with the related experimental data and its propriety is verified. The model is then used to explore the influence of various factors, including the diameter of boiling vapor bubbles, liquid density, liquid viscosity and the total heating power acted on the moderator cell, on the void fraction profiles in the cell. The results calculated with the present model indicate that the void fraction in the moderator cell increases linearly with heating power, and increases with the liquid viscosity, but decreases as the size of bubbles increases, and increases linearly with heating power. For the case where hydrogen is being used as a moderator, calculation results show that the void fraction in the moderator cell may be less than 30%, which is the maximum void fraction permitted from the nuclear physics point of view. The model and the calculation results will help to obtain insight of the mechanism that controls the void fraction distribution in the moderator cell, and provide theoretical supports for the moderator cell design.
|
|
| 8. |
- Li, Liangxing, et al.
(författare)
-
冷中子源冷包截面含汽率数理模型探讨
- 2005
-
Ingår i: Proceedings of the 11<sup>th</sup> Annual Meeting of Chinese Engineering Thermophysics.
-
Konferensbidrag (refereegranskat)
|
|
| 9. |
- Li, Liangxing, et al.
(författare)
-
冷中子源冷包截面含汽率数理模型探讨
- 2007
-
Ingår i: Gongcheng Rewuli Xuebao. - Beijing, China. - 0253-231X. ; 28, s. 64-67
-
Tidskriftsartikel (refereegranskat)abstract
- 文章推导出一种计算冷包截面含汽率的数学模型;将模型计算结果与已知文献相关实验结果进行对比,验证了模型的正确性.利用该模型探讨了冷包截面含汽率的影响因素如气泡直径,工质液体的密度、粘性,加热功率等.模型计算表明:气泡直径越大,在同一截面高度处的截面含汽率越低;工质粘性越大,在同一截面高度处的截面含汽率越高.本文模型的计算结果能对冷包设计提供理论支持.
|
|
| 10. |
- Li, Liangxing, et al.
(författare)
-
熔融液滴与冷却剂相互作用实验中液滴释放控制机构的研制
- 2008
-
Ingår i: Hedongli Gongcheng. - ChengDu, China. - 0258-0926. ; 29, s. 42-45
-
Tidskriftsartikel (refereegranskat)abstract
- 在高温熔融液滴与冷却剂相互作用的实验中,熔融液滴的释放控制对整个实验起至关重要的作用。本文在以往实验机械控制装置的基础上,自主设计一个自动控制电路来代替人工机械操作,利用控制电路给电磁铁提供瞬时脉冲来控制液滴瞬时释放下落,简化实验的可持续性操作,提高实验的重复性、精确性和操作方便性。
|
|
| 11. |
- Li, Liangxing, et al.
(författare)
-
熔融液滴在冷却剂中的运动特性实验
- 2007
-
Ingår i: Hedongli Gongcheng. - Chengdu, China. - 0258-0926. ; 28, s. 36-41
-
Tidskriftsartikel (refereegranskat)abstract
- 设计、建立了研究高温熔融液滴与冷却剂相互作用的可视化实验装置,通过高速摄影记录熔融液滴的下落过程,获得了下落小球运动过程曲线,重点考察了液滴温度和冷却剂温度对液滴-冷却剂界面作用过程的影响。结果表明,熔融液滴穿过气-水界面后,将首先经历一个速度骤降-回升过程,之后液滴作减速运动下落;当冷却水温度一定时,高温熔融液滴温度越高,熔融液滴入水后下落速度越快;当熔融液滴温度一定时,冷却水温度越高,熔融液滴入水后下落速度越快。
|
|
| 12. |
- Li, Xiangyu, et al.
(författare)
-
Identification of two-phase flow pattern in porous media based on signal feature extraction
- 2022
-
Ingår i: Flow Measurement and Instrumentation. - : Elsevier BV. - 0955-5986 .- 1873-6998. ; 83
-
Tidskriftsartikel (refereegranskat)abstract
- The statistical analysis methods based on differential pressure signals of two-phase flow are employed in the present study to identify the flow patterns in packed porous bed. The typical flow pattern images of two-phase flow in the packed porous beds are recognized and the corresponding differential pressure signals are recorded based on the visualization experiments. Then the statistical analysis methods, including probability density function (PDF), power spectral density (PSD), and wavelet energy spectrum (WES), are employed to extract the features of differential pressure signals in the time domain, frequency domain, and time-frequency domain respectively. The dimensionless parameters are proposed as the evaluation index to quantify the differences among flow patterns. The results show that the PDF, PSD, and WES methods can effectively characterize different flow patterns in the time, frequency, and time-frequency domain, respectively. The comprehensive recognition efficiency is about 88.5% using the introduced dimensionless parameters.
|
|
| 13. |
- Li, Xiangyu, et al.
(författare)
-
Two-phase flow patterns identification in porous media using feature extraction and SVM
- 2022
-
Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322 .- 1879-3533. ; 156
-
Tidskriftsartikel (refereegranskat)abstract
- Rapid and accurate identification of two-phase flow patterns in porous media is of great significance to the chemical industry, petroleum and nuclear engineering, etc. Based on the different pressure signals of gas-liquid two-phase flow in a porous bed, the present work proposes an intelligent recognition method to identify the two-phase flow patterns in porous media by the technologies of feature extraction and support vector machine (SVM). The analysis techniques, including time domain (PDF), frequency domain (PSD) and time-frequency domain (Wavelet), are employed to extract and summarize the corresponding characteristics of differential pressure signals of flow patterns. The intelligent recognition models are developed to identify the two-phase flow patterns in porous media by SVM. The models are trained respectively based on the characteristics of time domain + frequency domain (TF-SVM model), time domain + wavelet (TW-SVM model) and frequency domain + wavelet (FW-SVM model). The overall identification accuracy of the optimal model (TW-SVM model) reaches 96.08%.
|
|
| 14. |
- Wang, Weishu, et al.
(författare)
-
二次启动前火箭发动机泵构件温度特性数值计算
- 2005
-
Ingår i: Journal of Propulsion Technology. - Beijing, China. - 1001-4055. ; 26, s. 292-295
-
Tidskriftsartikel (refereegranskat)abstract
- 用数值计算的方法研究了液体火箭发动机在二次启动前,发动机泵系统各构件的温度特性和泵腔含汽率。建立了基于集总参数法的发动机启动前排放过程中涡轮、泵及进口管的温度变化计算模型。排放冷却过程中冷却剂N2O4的单相强制对流换热系数用Dittus-Boelter公式计算,流动沸腾换热系数采用ShanMM强化模型。并对某液体火箭发动机二次启动前排放过程涡轮泵系统各构件温度变化和泵腔含汽率进行了计算,模型计算结果与试车数据吻合良好,研究结果表明,二次启动前的主动排放过程对泵壳体及进口管的冷却效果很好。
|
|
| 15. |
- Wang, Weishu, et al.
(författare)
-
滑行过程中火箭发动机泵系统各构件温度数值模拟
- 2005
-
Ingår i: Journal of Propulsion Technology. - Beijing, China. - 1001-4055. ; 26, s. 394-397
-
Tidskriftsartikel (refereegranskat)abstract
- 利用数值计算的方法,研究了某型液体火箭发动机泵系统各构件及泵腔残余氧化剂在二次启动前滑行过程的温度变化。基于集总参数法建立了温度变化计算模型,并建立了泵腔残余氧化剂排空计算模型。计算结果与试车数据吻合良好。滑行过程中,涡轮温度下降,而泵壳体及进口管的温度升高;泵腔中残余氧化剂间歇排放。研究结果表明,滑行结束时泵系统的温度高于100℃,泵腔中残余氧化剂含汽率为1,不满足二次点火启动条件。
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Gong, Shengjie, et al.
(författare)
-
An experimental study on the effect of liquid film thickness on bubble dynamics
- 2013
-
Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 51:1-2, s. 459-467
-
Tidskriftsartikel (refereegranskat)abstract
- Experiments were conducted to investigate the boiling phenomenon in various liquid layers on a silicon heater surface with an artificial cavity. Deionized water is employed as working liquid. The emphasis is placed on how the liquid layer thickness affects bubble behaviour and liquid layer integrity for nucleate boiling under the isolated bubble regime. The experimental results show that for boiling in a liquid layer of ∼7.5 mm, the bubble dynamics reproduce the typical pool boiling characteristics with the averaged maximum diameter of 3.2 mm for the isolated bubbles growing on the cavity. As the water layer thickness decreases to the level comparable with the bubble departure diameter, the bubble is found to remain on the heater surface for an extended period, with a dry spot forming under the bubble but rewetted after the bubble rupture occurs. Further reducing the liquid layer thickness, an irreversible dry spot appears, suggesting a minimum rewettable thickness ranging from 1.2 mm to 1.9 mm corresponding to heat flux of 26 kW/m2 to 52 kW/m2. The void measured in the cavity confirms that it is dry inside the artificial cavity at high heat flux.
|
|
| 19. |
- Li, Liangxing, et al.
(författare)
-
An Experimental Study on Dryout Heat Flux in Particulate Bed Packed with Irregular Particles
- 2011
-
Ingår i: Proceedings of the 2011 international congress on advances in nuclear power plants. - : American Nuclear Society.
-
Konferensbidrag (refereegranskat)abstract
- This paper is concerned with reducing uncertainty in quantification of debris bed coolability in ahypothetical severe accident of light water reactors (LWRs), when the molten corium is relocatedinto a water pool, fragmenting and forming a particulate debris bed on the pool bottom.The test facility POMECO-HT at KTH is employed to investigate the coolability of particulatebeds which have some characteristics of a prototypical debris bed, such as packed with particlesof multiple sizes and irregular shapes. The facility features a high power capacity (up to 2.1MW/m2) which enables to obtain the dryout heat flux of a particulate bed formed by the DEFORparticles [1-2] for top-flooding and bottom-injection schemes. The particulate beds are chosen insuch a way that some characteristics of debris bed prototypicality analyzed in our previous study[3] can be reflected, so that the data can be used to confirm the previous analysis results. Threeparticulate beds, named Bed-1 through Bed-3, were employed in the present study to obtain thecorresponding dryout heat fluxes. Bed-1 and Bed-2 are both packed with sand particles whosesize distributions are similar to that of the DEFOR debris particles, with Bed-2 having a simulantcake embedded in the upper layer of the bed. Bed-3 is packed with DEFOR debris particles.The experimental results show that the dryout heat flux of the top-flooding beds can be predictedb y the Reed’s model. The bottom injection of coolant increases the dryout heat flux significantly,i.e., with an increase in water injection flowrate, the value of dryout heat flux is elevated.Meanwhile, the elevation of dryout position is moving upwards with increasing bottom-injectionflowrate. When a cake exits in a particulate bed, the dryout heat flux of the bed is significantlydecreased (up to 50%), and the dryout points a l w a y s located in the cake, for both the topflooding and bottom-fed configurations.
|
|
| 20. |
- Li, Liangxing, et al.
(författare)
-
An experimental study on pressure drop and dryout heat flux of two-phase flow in packed beds of multi-sized and irregular particles
- 2012
-
Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 242, s. 369-378
-
Tidskriftsartikel (refereegranskat)abstract
- This paper is concerned with debris bed coolability in a postulated severe accident of light water reactors, where the debris particles are irregular and multi-sized. To obtain and verify the friction laws predicting the hydrodynamics of the debris beds, the drag characteristics of air/water single- and two-phase flow in a particulate bed packed with multi-sized spheres or irregular sand particles were investigated on the POMECO-FL test facility. The same types of particles were then loaded in the test section of the POMECO-HT facility to obtain the dryout heat fluxes of the particulate beds heated volumetrically. The effective (mean) particle diameter is 2.25 mm for the multi-sized spheres and 1.75 mm for the sand particles, determined from the Ergun equation and the measured pressure drop of single-phase flow through the packed bed. Given the effective particle diameter, both the pressure drop and the dryout heat flux of two-phase flow through the bed can be predicted by the Reed model. The experiment also shows that the bottom injection of coolant improves the dryout heat flux significantly and the first dryout position is moving upward with increasing bottom injection flowrate. Compared with top-flooding case, the dryout heat flux of the bed can be doubled if the superficial velocity of coolant injection is 0.21–0.27 mm/s. The experimental data provides insights for interpretation of debris bed coolability (how to deal with the multi-sized irregular particles), as well as high-quality data for validation of the coolability analysis models and codes.
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
- Li, Liangxing, et al.
(författare)
-
Experimental characterization of the effective particle diameter of a particulate bed packed with multi-diameter spheres
- 2011
-
Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 241:5, s. 1736-1745
-
Tidskriftsartikel (refereegranskat)abstract
- This paper is concerned with uncertainty reduction in coolability analysis of a debris bed formed in fuel coolant interactions (FCI) during a postulated severe accident of LWRs. A test facility named POMECO-FL was designed and set up to investigate the friction laws of adiabatic single and two-phase flow through particulate beds which have the characteristics of the prototypical debris bed, such as packed with particles of multiple sizes or irregular shapes. The emphasis of the present study is placed on quantification of effective particle diameter of a particulate bed composed of multi-diameter spheres. Pressure drops are measured for water/air flow through the particulate beds packed with various combinations of spheres, and the effective particle diameters of the beds are obtained based on the pressure gradients and the Ergun equation. The results show that at low flowrate (Re < 7) the effective particle diameters can be represented by the area mean diameters of the particles in the beds, while at high velocity (Re > 7)the effective particle diameters are closer to the length mean diameters. If the area mean diameters are chosen as the effective particle diameters, the frictional pressure drops of two-phase flow in the beds can be predicted by the Reed model with good agreements.
|
|
| 24. |
|
|
| 25. |
- Li, Liangxing, et al.
(författare)
-
Experimental Study of Two-Phase Flow Regime and Pressure Drop in a Particulate Bed Packed with Multidiameter Particles
- 2012
-
Ingår i: Nuclear Technology. - : American Nuclear Society. - 0029-5450 .- 1943-7471. ; 177:1, s. 107-118
-
Tidskriftsartikel (refereegranskat)abstract
- This paper documents an experimental study on two-phase flow regimes and frictional pressure drop characteristics in a particulate (porous) bed packed with multidiameter (1.5-, 3-, and 6-mm) glass spheres. The experimental results provide new data to validate/develop hydrodynamic models for coolability analysis of debris beds formed in fuel-coolant interactions during a postulated severe accident. The POMECO-FL test facility is employed to perform the experiment, with the spheres packed in a test section of 90 mm diameter and 635 mm height. The pressure drops are measured for air/water two-phase flow through the packed bed, and flow patterns are obtained by means of visual observations. Meanwhile, local void fraction in the center of the bed is measured by a microconductive probe.The experimental results show that the frictional pressure drop of single-phase flow through the bed can be predicted by the Ergun equation, if the area mean diameter of the particles is chosen in the calculation. Given the so-determined effective particle diameter, the estimation of the Reed model for two-phase flow pressure gradient in the bed has a good agreement with the experimental data. The characteristics of the local void fraction can be used to predict flow pattern and mean void fraction. It is observed that slug flow prevails when the mean void fraction is <0.5, whereas annular flow dominates after the mean void fraction is >0.7. If the effective particle diameter is further used as an influential parameter in flow pattern identification, the observed flow regimes of two-phase flow in porous media are well predicted by the existing flow pattern map.
|
|
| 26. |
|
|
| 27. |
- Li, Liangxing, et al.
(författare)
-
Experimental Study on the Effective Particle Diameter of a Packed Bed with Non-Spherical Particles
- 2011
-
Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 89:1, s. 35-48
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental study is conducted to determine the characteristics of frictional pressure drops of fluid flow in porous beds packed with non-spherical particles. The objective is to examine the applicability of the Ergun equation to flow resistance assessment for packed beds with non-spherical particles. The experiments are carried out on the POMECOFL facility at KTH. Hollow spheres and cylinders are used to pack the beds. Either water or air is chosen as the working fluid. The experimental data show that the Ergun equation is applicable to all the test beds if the effective particle diameter used in the equation is chosen as the equivalent diameter of the particles, which is the product of Sauter mean diameter and shape factor of the particles in each bed.
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
- Thakre, Sachin, 1984-, et al.
(författare)
-
A numerical analysis on hydrodynamic deformation of molten droplets in a water pool
- 2013
-
Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 53, s. 228-237
-
Tidskriftsartikel (refereegranskat)abstract
- Motivated by basic understanding on the single-droplet steam explosion phenomenon, the present study is concerned with the simulation of the molten droplet preconditioning (deformation/pre-fragmentation) during the initial phase of the fuel coolant interaction (FCI) by using the CFD code FLUENT through the Volume of Fluid (VOF) method. Due to the complexity of the problem, only the hydrodynamics of the multiphase system, without heat transfer, is considered. Calculations were performed for various configurations (melt-coolant two-phase system, and melt-coolant-vapor three-phase system) demonstrating that the current approach is capable of capturing the interfaces between the phases (melt, water and vapor) and predicting the droplet behavior with a reasonable mass conservation. A melt droplet disturbed by an external trigger is also analyzed, as well as the effect of the pressure pulse magnitude on the severity of droplet deformation. The MISTEE experimental data was used as a benchmark for the validation of the performed calculations. The results of the separate-effect study quantitatively demonstrate the importance of droplet velocity and melt properties on the melt droplet preconditioning.
|
|
| 31. |
- Thakre, Sachin, et al.
(författare)
-
A Numerical Analysis on the Hydrodynamics of a Single Droplet in a Water Pool
- 2011
-
Ingår i: Proceedings of the international congress on advances in nuclear power plants. - : American Nuclear Society.
-
Konferensbidrag (refereegranskat)abstract
- The droplet behavior in coolant is one of the key phenomena that govern the dynamics and energetics of molten fuel coolant interactions (FCI) during a hypothetical severe accident of a light water reactor (LWR). The violent interaction between molten fuel droplets and coolant may lead to a steam explosion that shall challenge the containment integrity. Although an extensive research on steam explosion was conducted to investigate, the understanding of steam explosion energetics is still limited because of the complexity of the phenomenology involving intense thermal-hydrodynamics. The recent work at KTH [1-2] for was focused on the micro interactions of a single droplet with coolant by using a delicate test setup and a novel visualization system (simultaneous high-speed acquisition using x-ray radiography and photography), and it was found that the preconditioning (deformation/pre-fragmentation) of a droplet is instrumental to the resulting steam explosion. With the high-temperature molten droplet falling into the volatile liquid coolant, the droplet surface experiences intensive film boiling, and the formation of the vapor film on the droplet surface also contributes to the preconditioning of the droplet. In one of hypothetical mechanisms of steam explosion, for example, it is believed that the collapse of the vapor film, triggered by a shock wave, is the cause of steam explosion due to the direct contact between melt and coolant. The present study is to simulate and reproduce the preconditioning (deformation/pre-fragmentation) of the droplet by using the commercial CFD code ANSYS Fluent through the Volume of Fluid (VOF) method and User Defined Function (UDF). Since the existence of the intense heat and mass transfer in the multiphase systems presents considerable difficulties in the accurate simulation of the processes, the current simulation is only limited to hydrodynamics of the droplet and its vapor film in a water pool, without consideration of further phase change after film boiling. Due to the focus of the study being placed on the preconditioning whose time scale is quite short (in milliseconds), such a simplification does not lose the key physics of the process. To save the commutating time, a two-dimensional domain of 20mm×50mm is chosen in the computational analysis with a droplet of 3mm in initial diameter covered by a vapor film. The droplet is falling at a certain initial velocity (selected from 0 to 5 m/s). The initial thickness of the vapor film is also varied for a parametric study to see its effect on the deformation of the droplet. For further separate-effect study, analyses are also carried out with different surface tensions and viscosity values to gain insights of the effects of the melt material properties on steam explosion in hypothetical severe accidents of a LWR. As a part of the analysis, a shock wave is introduced inside the domain from one of the boundaries, to investigate the interfacial instability which is of importance to the triggering phase of a steam explosion.
|
|
| 32. |
- Thakre, Sachin, et al.
(författare)
-
An experimental study on coolability of a particulate bed with radial stratification or triangular shape
- 2014
-
Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 276, s. 54-63
-
Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the results of an experimental study on the coolability of particulate beds with radial stratification and triangular shape, respectively. The study is intended to get an idea on how the coolability is affected by the different features of a debris bed formed in a severe accident of light water reactors. The experiments were performed on the POMECO-HT facility which was constructed to investigate two-phase flow and heat transfer in particulate beds under either top-flooding or bottom-fed condition. A downcomer is designed to enable investigation of the effectiveness of natural circulation driven coolability. Two homogenous beds were also employed in the present study to compare their dryout power densities with those of the radially stratified bed and the triangular bed. The results show that the dryout heat fluxes of the homogeneous beds at top-flooding condition can be predicted by the Reed model. For the radially stratified bed, the dryout heat flux is dominated by two-phase flow in the columns packed with larger particles, and the dryout occurred initially near the boundary between the middle column and a side column. Given the same volume of particles under top-flooding condition, the dryout power density of the triangular bed is about 69% higher than that of the homogenous bed. The coolability of all the beds is enhanced by bottom-fed coolant driven by either forced injection or downcomer-induced natural circulation.
|
|
| 33. |
- Zhang, Zhengzheng, et al.
(författare)
-
Experimental and numerical studies on the two-dimensional flow characteristics in the radially stratified porous bed
- 2022
-
Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier BV. - 0735-1933 .- 1879-0178. ; 133, s. 105940-
-
Tidskriftsartikel (refereegranskat)abstract
- The experiment and numerical simulations are both conducted in the present study to better understand the twodimensional flow characteristics in the radially stratified porous bed. Spherical particles of two different sizes are packed in the left part and right part of a cylindrical test section separately to form a two-layer bed with the configuration of radial stratification. The variations of pressure drops in each part of the stratified bed are measured when water flows up through the packed bed. Meanwhile, the numerical simulation is also carried out to investigate the flow field in the stratified bed, especially the flow characteristics around the interface of two parts. The results indicated that the pressure drops in the two layers of radial stratified bed are almost equal. When the fluids flow up through the radially stratified porous layers, the lateral flowing from the low permeability layer to the high permeability layer leads to a decrease of pressure drop in the low permeability layer and an increase of pressure drop in the high permeability layer. Most of the lateral flow occurs in the initial part of the test section. Besides, the lateral and vertical pressure gradient can be well predicted by Ergun equation respectively.
|
|
| 34. |
- Zhang, Zhengzheng, et al.
(författare)
-
Investigation on Flow Characteristics in Radial Stratified Debris Bed
- 2022
-
Ingår i: Yuanzineng Kexue Jishu/Atomic Energy Science and Technology. - : Atomic Energy Press. - 1000-6931. ; 56:10, s. 2032-2040
-
Tidskriftsartikel (refereegranskat)abstract
- During the severe accident of light water reactors (LWRs), the particulate debris bed with porous structure may be formed at different places in the reactor after molten corium fuel coolant interaction (FCI). The coolability of the debris bed therefore plays an important role in corium risk quantification, which is crucial to the stabilization and termination of a severe accident in LWRs. Many experimental and analytical studies have been conducted towards quantitative understanding of debris bed coolability. However, most of previous studies were conducted based on the homogeneous debris beds packed with single size particles, and only a few investigations were performed with the heterogeneous debris beds like stratified debris bed. In fact, scoping studies on debris bed formation and configuration based on FCI experiments indicate that the stratified debris bed would be most expected. In order to study the flow characteristics in heterogeneous debris beds, the packed porous beds with radial stratification were constructed in the present study using two different sizes glass spheres with the diameter of 2 mm and 8 mm respectively. Besides, the homogeneous packed beds packed with single size particles and uniform mixture by the above two size particles were also constructed for comparison. The particles were packed in a cylindrical test section with the inner diameter of 120 mm and the height of 600 mm. Single-phase flow tests were performed on the homogeneous beds and heterogeneous bed firstly to investigate the flow resistance characteristics in the packed beds with different configurations. Then numerical simulation was also conducted to reveal the flow redistribution of stratified bed, especially on the flow field at the stratified interface. The experimental results show that the pressure drops of single-phase flow in the homogeneous beds can be well predicted by Ergun equation. For the radial stratified packed bed with different permeability layers, the pressure drops in each layer of the stratified bed are almost equal and increase with the liquid inlet flowrate. Comparing with those in the homogenous beds packed with the same size particles as those in different layer of stratified bed, the pressure drops in the stratified bed are much lower than those of homogenous bed packed with smaller size particles, while slightly higher than those with larger size particles. The numerical simulation results state that there is a two-dimensional flow phenomenon in the radial stratified bed. In addition to dominate upward flow in the stratified bed, a lateral flow flows from low permeability layer to high permeability layer. The two-dimensional flow in stratified bed decreases the flowrate and pressure drops in low permeability layer and increases the pressure drops in high permeability layer. With the increase of liquid flowrate, the average lateral flowrate at the stratified interface increases, but the ratio of lateral volume flowrate to total fluid volume flowrate decreases.
|
|
