Numerical analysis for FP speciation in VERDON-2 experiment: Chemical re-vaporization of iodine in air ingress condition

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.

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Experiment and Numerical Analysis of Control Method of Natural Circulation by Injection of Helium Gas

Volume 6: Beyond Design Basis Events; Student Paper Competition ◽

10.1115/icone21-16072 ◽

2013 ◽

Author(s):

Naoto Yanagawa ◽

Masashi Nomura ◽

Tetsuaki Takeda ◽

Shumpei Funatani

Keyword(s):

Numerical Analysis ◽

Mole Fraction ◽

Pressure Vessel ◽

Control Method ◽

Natural Circulation ◽

Circulation Flow ◽

Helium Gas ◽

Air Ingress ◽

The One ◽

Reactor Pressure

This study is to investigate a control method of the natural circulation of the air by the injection of helium gas. A depressurization is the one of the design-basis accidents of a Very High Temperature Reactor (VHTR). When the primary pipe rupture accident occurs in the VHTR, the air is predicted to enter into the reactor pressure vessel from the breach and oxidize in-core graphite structures. Finally, it seems to be probable that the natural circulation flow of the air in the reactor pressure vessel produce continuously. In order to predict or analyze the air ingress phenomenon during the depressurization accident of the VHTR, it is important to develop the method for prevention of air ingress during the accident. In this study, the air ingress process is discussed by comparing the experimental and analytical results of the reverse U-shaped channel which has parallel channels. The experiment of the natural circulation using a circular tube consisted of the reverse U-shaped type has been carried out. The vertical channel is consisted of the one side heated and the other side cooled pipe. The experimental apparatus is filled with the air and one side vertical tube is heated. A very small amount of helium gas is injected from the top of the channel. The velocity and the mole fraction of each gas are also calculated by using heat and mass transfer numerical analysis of multi-component gas. The result shows that the numerical analysis is considered to be well simulated the experiment. The natural circulation of the air has very weak velocity after the injection of helium gas. About 780 seconds later, the natural circulation suddenly produces. The natural circulation flow of the air can be controlled by the method of helium gas injection. The mechanism of the phenomenon is found that mole fraction is changed by the molecular diffusion and the very weak circulation.

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

Volume 3: Thermal-Hydraulics ◽

10.1115/icone24-60990 ◽

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.

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Numerical Analysis on Air Ingress Behavior in GTHTR300-Cogeneration System

Journal of Power and Energy Systems ◽

10.1299/jpes.1.24 ◽

2007 ◽

Vol 1 (1) ◽

pp. 24-35 ◽

Cited By ~ 4

Author(s):

Tetsuaki TAKEDA ◽

Xing YAN ◽

Kazuhiko KUNITOMI

Keyword(s):

Numerical Analysis ◽

Cogeneration System ◽

Air Ingress

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Numerical analysis on air ingress behavior in GTHTR300 system

The Proceedings of the National Symposium on Power and Energy Systems ◽

10.1299/jsmepes.2004.9.281 ◽

2004 ◽

Vol 2004.9 (0) ◽

pp. 281-284

Author(s):

Tetsuaki TAKEDA ◽

Xing YAN ◽

Kazuhiko KUNITOMI

Keyword(s):

Numerical Analysis ◽

Air Ingress

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Numerical Analysis on Air Ingress Behavior in GTHTR300H

Volume 3: Structural Integrity; Nuclear Engineering Advances; Next Generation Systems; Near Term Deployment and Promotion of Nuclear Energy ◽

10.1115/icone14-89673 ◽

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

Volume 6: Thermal-Hydraulics ◽

10.1115/icone25-67750 ◽

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.

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