Development of Prevention Method for Air Ingress During a Depressurization Accident of the VHTR

2016 ◽  
Author(s):  
Tetsuaki Takeda ◽  
Shumpei Funatani
Keyword(s):  
Natural Convection ◽  
Numerical Analysis ◽  
Storage Tank ◽  
Molecular Diffusion ◽  
Fluid Layer ◽  
Natural Circulation ◽  
Flow Characteristics ◽  
Mixing Process ◽  
Vertical Slot ◽  
Air Ingress

A depressurization accident is a design-basis accidents of a very high temperature reactor. When a depressurization accident occurs, air is expected to enter the reactor pressure vessel from the breach and oxidize in-core graphite structures. Therefore, it is important to know a mixing process of different kind of gases in the stable and unstable stratified fluid layer. Especially, it is also important to examine an influence of localized natural convection and molecular diffusion on mixing process from a viewpoint of safety. In order to predict and analyze the phenomena of air ingress during a depressurization accident, therefore, it is important to develop the method for prevention of air ingress during the accident. We have carried out an experiment and a numerical analysis using three-dimensional computational fluid dynamics (3D CFD) to obtain the mixing process of two component gases and flow characteristics of the localized natural convection. This study is also to investigate a control method of natural circulation of air by injection of helium gas. The numerical model consists of a storage tank and a reverse U-shaped vertical slot. They are separated by a partition plate. One side of the left wall of the left side vertical slot is heated and the other side was cooled. The right side vertical slot is cooled. The procedure of the experiment and the numerical analysis is as follows. Firstly, the storage tank was filled with heavy gas and the reverse U-shaped vertical slot was filled with light gas. In the left side vertical slot, the localized natural convection was generated by the temperature difference between the vertical walls. The flow characteristics were obtained by the experiment and steady state analysis. The unsteady state experiment and analysis were started after the partition plate was opened. The result obtained in the experiment was simulated by the numerical analysis quantitatively. The gases were mixed by molecular diffusion and natural convection. After the time elapsed, natural circulation occurred. When the temperature difference of the left vertical fluid layer was set to 100K and the combination of the mixed gas was helium and nitrogen, natural circulation produced after 110 minutes elapsed.

Experimental and Numerical Analysis of Mixing Process of Two Component Gases in a Vertical Fluid Layer in a VHTR

2019 ◽  
Vol 5 (2) ◽  
Author(s):  
Tetsuaki Takeda
Keyword(s):  
High Temperature ◽  
Natural Convection ◽  
Numerical Analysis ◽  
Pressure Vessel ◽  
Storage Tank ◽  
Molecular Diffusion ◽  
Flow Characteristics ◽  
Mixing Process ◽  
Two Component ◽  
Air Ingress

When a depressurization accident of a very-high-temperature reactor (VHTR) occurs, air is expected to enter into the reactor pressure vessel from the breach and oxidize in-core graphite structures. Therefore, in order to predict or analyze the air ingress phenomena during a depressurization accident, it is important to develop a method for the prevention of air ingress during an accident. In particular, it is also important to examine the influence of localized natural convection and molecular diffusion on the mixing process from a safety viewpoint. Experiment and numerical analysis using a three-dimensional (3D) computational fluid dynamics code have been carried out to obtain the mixing process of two-component gases and the flow characteristics of localized natural convection. The numerical model consists of a storage tank and a reverse U-shaped vertical rectangular passage. One sidewall of the high-temperature side vertical passage is heated, and the other sidewall is cooled. The low-temperature vertical passage is cooled by ambient air. The storage tank is filled with heavy gas and the reverse U-shaped vertical passage is filled with a light gas. The result obtained from the 3D numerical analysis was in agreement with the experimental result quantitatively. The two component gases were mixed via molecular diffusion and natural convection. After some time elapsed, natural circulation occurred through the reverse U-shaped vertical passage. These flow characteristics are the same as those of phenomena generated in the passage between a permanent reflector and a pressure vessel wall of the VHTR.

Experiment and Numerical Analysis of Mixing Process of Two Component Gases in Vertical Fluid Layer

2017 ◽  
Author(s):  
Tetsuaki Takeda
Keyword(s):  
High Temperature ◽  
Natural Convection ◽  
Numerical Analysis ◽  
Molecular Diffusion ◽  
Natural Circulation ◽  
Flow Characteristics ◽  
Mixing Process ◽  
High Temperature Side ◽  
Two Component ◽  
Air Ingress

A depressurization accident is the one of the design-basis accidents of a Very-High-Temperature Reactor (VHTR). When a depressurization accident occurs, air is expected to enter into the reactor pressure vessel from the breach and oxidize in-core graphite structures. Therefore, it is important to understand the mixing processes of different kinds of gases in the stable and unstable stratified fluid layers. In particular, it is also important to examine the influence of localized natural convection and molecular diffusion on the mixing process from a safety viewpoint. Therefore, in order to predict or analyze the air ingress phenomena during a depressurization accident, it is important to develop a method for the prevention of air ingress during an accident. We carried out experiments and numerical analysis using three-dimensional (3D) CFD code to obtain the mixing process of two-component gases and the flow characteristics of localized natural convection. This study also investigated a control method for the natural circulation of air through the injection of helium gas. The numerical model consists of a storage tank and a reverse U-shaped vertical rectangular passage. They are separated by a horizontal partition plate. One sidewall of the high-temperature side vertical passage is heated and the other sidewall is cooled. The low-temperature vertical passage is cooled by ambient air. The storage tank is filled with heavy gas and the reverse U-shaped vertical passage is filled with a light gas. In the vertical passage of the high-temperature side, localized natural convection is generated by the temperature difference between the vertical walls. The results obtained from the experiments were quantitatively simulated using 3D numerical analysis. The two component gases were mixed via molecular diffusion and natural convection. After some time elapsed, natural circulation occurred through the reverse U-shaped vertical passage. These flow characteristics are the same as those of phenomena generated in the passage between a permanent reflector and a pressure vessel wall of the VHTR.

Study on Mixing Process of Two Component Gases in a Vertical Fluid Layer: Effectiveness on One-Dimensional Natural Circulation

2012 ◽  
Author(s):  
Hiroki Mizuno ◽  
Tetsuaki Takeda ◽  
Shumpei Funatani
Keyword(s):  
Natural Convection ◽  
Molecular Diffusion ◽  
Fluid Layer ◽  
Natural Circulation ◽  
Stratified Fluid ◽  
Heated Wall ◽  
Gas Mixture ◽  
Mixing Process ◽  
Vertical Slot ◽  
Two Component

This study is to investigate an effect of natural convection or natural circulation on a transport process by molecular diffusion in a stratified fluid layer consisting of two component gases. There are many experiment and analysis regarding natural convection or natural circulation in the vertical slot. However, there are few studies on natural convection or circulation and molecular diffusion in the stratified fluid layer consisting of two component gases. It was confirmed that these phenomena appear when the depressurization accident occurs in the very high temperature reactor (VHTR). Therefore it is important to evaluate the transport and mixing processes during the depressurization accident of the VHTR. The experiment has been performed regarding the combined phenomena of molecular diffusion and natural convection or circulation in a two parallel vertical slots filled with two component gases. The vertical slot consists of the one side heated wall and the other side cooled wall. The other slot consists of the two cooled walls. The dimension of heated wall is 500mm×200mm and thickness is 3mm. The width of the slot is 20mm and the aspect ratio is 25. Combination of nitrogen(N2)/argon(Ar), neon(Ne)/argon(Ar), helium(He)/nitrogen(N2) and helum(He)/argon(N2) was used as the first step of the experiment of the two component gases. The density change of the gas mixture and the gas temperature distribution in the slots were obtained. The mixing process of the heavier gas from the bottom side of the slot filled with the lighter gas was discussed in this paper. The experimental results showed that the transport phenomena by the molecular diffusion were influenced by the localized natural convection or circulation of the gas mixture in the stratified fluid layer. From the experimental results, it was found that the mixing process by molecular diffusion was affected significantly by the natural convection or circulation induced by the slight temperature difference between both vertical walls.

Development of Prevention Method for Air Ingress During a Pipe Rupture Accident of the VHTR: Effectiveness on Localized Natural Convection

2017 ◽  
Author(s):  
Yudai Tanaka ◽  
Tetsuaki Takeda
Keyword(s):  
Natural Convection ◽  
Storage Tank ◽  
Molecular Diffusion ◽  
Control Method ◽  
Natural Circulation ◽  
Onset Time ◽  
Mixing Process ◽  
Helium Gas ◽  
Air Ingress ◽  
Heavy Gas

A primary pipe rupture accident is one of the design-basis accidents of a Very-High-Temperature Reactor (VHTR). When a primary pipe rupture accident occurs, air is expected to enter into the reactor pressure vessel from the breach and oxidize in-core graphite structures. Therefore, it is important to understand the mixing processes of different kinds of gases in the stable and unstable stratified fluid layers. In particular, it is also important to examine the influence of localized natural convection and molecular diffusion on the mixing process from a safety viewpoint. Therefore, in order to predict or analyze the air ingress phenomena during a pipe rupture accident, it is important to develop a method for the prevention of air ingress during an accident. We carried out experiments to obtain the mixing process of two-component gases and flow characteristics of localized natural convection. This study also investigated a control method for the natural circulation of air through the injection of helium gas. An experiment has been carried out to investigate a control method of natural circulation of air by injection of helium gas. The experimental apparatus consists of a reverse U-sharped vertical slot and a storage tank. One side-slot consists of the heated and cooled walls. The other side-slot consists of the two cooled walls. The dimensions of the vertical slots are 598 mm in height, 208 mm in depth, and 70 mm in width. Each two vertical slots were connected and were a reverse U-shaped passage. The dimensions of the connecting passage were 16 mm in height, 106 mm in depth, and 210 mm in length. The storage tank was connected to the lower part of the reverse U-shaped passage. The dimensions of the storage tank were 398 mm in length, 398 mm in depth, and 548 mm in width. The reverse U-shaped passage and the storage tank were separated by a partition plate. The wall and gas temperature were measured by a K-type thermocouple. Experimental results regarding mixing process of two component gases in vertical fluid layer were as follows. The heavy gas was transported to the slot by the molecular diffusion and natural convection. As time elapses, natural circulation of heavy gas suddenly occurs through the reverse U-shaped slot. As a result of experiments, the onset time of natural circulation is affected by not only molecular diffusion coefficient but also the strength of natural convection. When the helium gas is injected into the channel, it is possible to control the natural circulation of air. The onset time of the reproduction of the natural circulation can be varied by changing the injection rate of the helium gas.

Study on the Effect of One-Dimensional Natural Circulation on the Mixing Process of Two Component Gases

2014 ◽  
Author(s):  
Shumpei Funatani ◽  
Tetsuaki Takeda
Keyword(s):  
Natural Convection ◽  
Temperature Difference ◽  
Molecular Diffusion ◽  
Fluid Layer ◽  
Natural Circulation ◽  
Onset Time ◽  
Mixing Process ◽  
Vertical Slot ◽  
Two Component ◽  
Density Ratios

This study is to investigate the effect of one-dimensional natural circulation on the mixing process of two component gases by evaluating the onset time of natural circulation through the apparatus under the stable density stratified fluid layer. The experimental apparatus consists of a reverse U-shaped vertical slot and a storage tank. The left side vertical slot consists of the heated wall and the cooled wall. The right side vertical slot consists of the two cooled walls. Temperature difference between the vertical walls was set to 50, 70, and 100 K. In this study, the combination of the two component gases is He/Ar and density ratio of each component is 1.4/10. The heavy gas was filled with the storage tank and light gas was filled with the reverse U-shaped vertical slot. Before the experiment starts, the localized natural convection was generated in the heated side vertical slot. After the experiment starts, the heavy gas will be transported to the slot by the molecular diffusion and natural convection. And then, natural circulation occurs abruptly through the reverse U-shaped passage. The mixing process of two component gases and the onset time of natural circulation in the vertical fluid layer were affected not only by the localized natural convection but also by the molecular diffusion. The wall and gas temperatures were measured by thermocouples and the velocity of natural convection was measured to evaluate the characteristics of the mixing process and the natural convection. These experimental results show that generation time of natural circulation was affected by molecular diffusion and localized natural convection. When the two components of gases have large density ratios and large Gr numbers, the mixing process of two components of gases was affected by more intensively molecular diffusion than localized natural convection when temperature difference was 50K. The mixing process of two component gas was affected by more intensively localized natural convection than molecular diffusion when temperature difference was 70 to 100K. However, two component gases were affected by more intensively molecular diffusion than localized natural convection at small density ratios and small Gr numbers.

Study on Mixing Process of Two Component Gases in a Stable Stratified Fluid Layer: Effectiveness on Natural Convection

2013 ◽  
Author(s):  
Tetsuaki Takeda ◽  
Shumpei Funatani
Keyword(s):  
Natural Convection ◽  
Molecular Diffusion ◽  
Fluid Layer ◽  
Natural Circulation ◽  
Stratified Fluid ◽  
Heated Wall ◽  
Gas Mixture ◽  
Mixing Process ◽  
Vertical Slot ◽  
Two Component

This study is to investigate an effect of natural convection or natural circulation on a transport process by molecular diffusion in a stratified fluid layer consisting of two component gases. There are many experiment and analysis regarding natural convection or natural circulation in the vertical slot. However, there are few studies on natural convection or circulation and molecular diffusion in the stratified fluid layer consisting of two component gases. It was confirmed that these phenomena appear when the depressurization accident occurs in the very high temperature reactor (VHTR). Therefore it is important to evaluate the transport and mixing processes during the depressurization accident of the VHTR. The experiment has been performed regarding the combined phenomena of molecular diffusion and natural convection or circulation in a two parallel vertical slots filled with two component gases. The vertical slot consists of the one side heated wall and the other side cooled wall. The other slot consists of the two cooled walls. The dimension of heated wall is 500mm×200mm and thickness is 3mm. The width of the slot is 20mm and the aspect ratio is 25. Combination of nitrogen (N2)/argon(Ar), neon(Ne)/Ar, helium(He)/N2 and He/Ar was used as the first step of the experiment of the two component gases. The density change of the gas mixture and the gas temperature distribution in the slots were obtained. The mixing process of the heavier gas from the bottom side of the slot filled with the lighter gas was discussed in this paper. The experimental results showed that the transport phenomena by the molecular diffusion were influenced by the localized natural convection or circulation of the gas mixture in the stratified fluid layer. From the experimental results, it was found that the mixing process by molecular diffusion was affected significantly by the natural convection or circulation induced by the slight temperature difference between both vertical walls.

Mixing Process of Two Component Gases by Natural Convection and Molecular Diffusion

2021 ◽  
Author(s):  
Takeaki Ube ◽  
Tetsuaki Takeda
Keyword(s):  
High Temperature ◽  
Natural Convection ◽  
Molecular Diffusion ◽  
Natural Circulation ◽  
Mixing Process ◽  
Circulation Flow ◽  
Experimental Apparatus ◽  
Two Component ◽  
High Temperature Reactor ◽  
Air Ingress

Abstract A depressurization accident involving the rupture of the primary cooling pipe of the Gas Turbine High Temperature Reactor 300 cogeneration (GTHTR300C), which is a very-high-temperature reactor, is a design-based accident. When the primary pipe connected horizontally to the side of the reactor pressure vessel of GTHTR300C ruptures, molecular diffusion and local natural convection facilitate gas mixing, in addition to air ingress by counter flow. Furthermore, it is expected that a natural circulation flow around the furnace will suddenly occur. To improve the safety of GTHTR300C, an experiment was conducted using an experimental apparatus simulating the flow path configuration of GTHTR300C to investigate the mixing process of a two-component gas of helium and air. The experimental apparatus consisted of a coaxial double cylinder and a coaxial horizontal double pipe. Ball valves were connected to a horizontal inner pipe and outer pipe, and the valves were opened to simulate damage to the main pipe. As a result, it was confirmed that a stable air and helium density stratification formed in the experimental apparatus, and then a natural circulation flow was generated around the inside of the reactor.

Transport Process by Natural Convection and Molecular Diffusion of Two Component Gases in a Stratified Fluid Layer

2011 ◽  
Author(s):  
Tetsuaki Takeda ◽  
Hirotaka Isomi ◽  
Hiroki Hanazawa
Keyword(s):  
Natural Convection ◽  
Transport Process ◽  
Molecular Diffusion ◽  
Fluid Layer ◽  
Natural Circulation ◽  
Stratified Fluid ◽  
The Other ◽  
Heated Wall ◽  
Vertical Slot ◽  
Two Component

This study is to investigate an effect of natural convection or natural circulation on a transport process by molecular diffusion in a stratified fluid layer consisting of two component gases. There are many experiments and analysis regarding natural convection in a vertical slot or natural circulation in a circular tube. However, there are few studies on natural convection or circulation with molecular diffusion in the stratified fluid layer consisting of two component gases. It is confirmed that these phenomena appear when the depressurization accident occurs in the very high temperature reactor (VHTR). Therefore it is important to evaluate the transport and mixing processes of two or more component gases during the depressurization accident of the VHTR. The experiment has been performed regarding the combined phenomena of molecular diffusion and natural convection or natural circulation in a parallel vertical slot filled with two component gases. The one vertical slot consists of the heated wall and the other side cooled wall. The other one consists of both the cooled wall. The dimension of heated wall is 500mm×200mm and thickness is 3mm. The width of the slot is 20mm and the aspect ratio of the slot is 25. Combination of nitrogen/argon is used as the two component gas system. The density change of the gas mixture and the gas temperature distribution in the slots were obtained. The mixing process of the heavier gas from the bottom side of the slot filled with the lighter gas was discussed in this paper.

Numerical Analysis on Air Ingress Behavior in GTHTR300H

2006 ◽  
Author(s):  
Tetsuaki Takeda ◽  
Xing Yan ◽  
Kazuhiko Kunitomi
Keyword(s):  
High Temperature ◽  
Numerical Analysis ◽  
Gas Turbine ◽  
Molecular Diffusion ◽  
Natural Circulation ◽  
Onset Time ◽  
Gas Mixture ◽  
Energy Agency ◽  
High Temperature Reactor ◽  
Air Ingress

Japan Atomic Energy Agency (JAEA) has been developing the analytical code for the safety characteristics of the HTGR and carrying out design study of the gas turbine high temperature reactor of 300MWe nominal-capacity for hydrogen production, the GTHTR300H (Gas Turbine High Temperature Reactor 300 for Hydrogen). The objective of this study is to clarify safety characteristics of the GTHTR300H for the pipe rupture accident. A numerical analysis of heat and mass transfer fluid flow with multi-component gas mixture has been performed to obtain the variation of the density of the gas mixture, and the onset time of natural circulation of air. From the results obtained in this analysis, it was found that the duration time of the air ingress by molecular diffusion would increase due to the existence of the recuperator in the GTHTR300H system.

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