Experiments and numerical analysis of a control method for natural circulation through helium gas injection

2016 ◽  
Vol 306 ◽  
pp. 108-116 ◽  
Author(s):  
Tetsuaki Takeda ◽  
Hirofumi Hatori ◽  
Shumpei Funatani
Keyword(s):  
Numerical Analysis ◽  
Control Method ◽  
Natural Circulation ◽  
Gas Injection ◽  
Helium Gas

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

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.

Study on control method of natural circulation by injection of helium gas

2014 ◽  
Vol 271 ◽  
pp. 417-423 ◽  
Author(s):  
Tetsuaki Takeda ◽  
Masashi Nomura ◽  
Naoto Yanagawa ◽  
Shumpei Funatani
Keyword(s):  
Control Method ◽  
Natural Circulation ◽  
Helium Gas

Development of Technique for Controlling Natural Circulation Flow by Using Helium Gas

2014 ◽  
Author(s):  
Hirofumi Hatori ◽  
Naoto Yanagawa ◽  
Tetsuaki Takeda ◽  
Shumpei Funatani
Keyword(s):  
Steady State ◽  
Pressure Vessel ◽  
Control Method ◽  
Natural Circulation ◽  
Vertical Channel ◽  
Vertical Tube ◽  
Reactor Pressure Vessel ◽  
Circulation Flow ◽  
Helium Gas ◽  
Reactor Pressure

The purpose of this study is to investigate a control method of natural circulation flow of air by injection of helium gas. A depressurization accident by the primary pipe rupture is one of the design-basis accidents of a Very High Temperature Reactor (VHTR). When the double coaxial duct connecting between a reactor core and an intermediate heat exchanger (IHX) module breaks, air is expected to enter the reactor pressure vessel from the breach and oxidize in-core graphite structures. Then, it seems to be probable that the natural circulation flow of air in the reactor pressure vessel produce continuously. In such condition, injection of helium gas into the channel by a passive method can prevent occurrence of the natural circulation flow of air in the reactor pressure vessel. Therefore, it is thought that oxidation of in-core graphite structures by air ingress can be prevented by establishing this method. The experiment has been carried out regarding the natural circulation flow using a circular tube consisting of a reverse U-shaped type. The vertical channel consists of one side heated tube and the other side cooled tube. The experimental procedure is as follows. Firstly, the apparatus is filled with air and one vertical tube is heated. Then, natural circulation of air will be produced in the channel. After the steady state is established, a small amount of helium gas is injected from the top of the channel. The velocity, mole fraction, temperature of gas, and temperature of the tube wall are measured during the experiment. The results were obtained as follows. When the temperature difference between the both vertical tubes was kept at about 60K, the velocity of the natural circulation flow of air was measured about 0.17m/s. During a steady state, a small amount of helium gas was injected into the channel. When the volume of injected helium gas is about 5.7% of the total volume of the channel, the velocity of the natural circulation flow of air became around zero. After 810 seconds elapsed, the natural circulation flow suddenly produced again. The natural circulation flow of air can be controlled by injecting of helium gas.

Study on Control Method of Natural Circulation by Injection of Helium Gas

2012 ◽  
Author(s):  
Masashi Nomura ◽  
Tetsuaki Takeda ◽  
Shumpei Funatani ◽  
Takuya Shimura
Keyword(s):  
Pressure Vessel ◽  
Control Method ◽  
Natural Circulation ◽  
Vertical Channel ◽  
Reactor Pressure Vessel ◽  
Experimental Results ◽  
Circulation Flow ◽  
Helium Gas ◽  
Air Ingress ◽  
Reactor Pressure

This study is to investigate a control method of natural circulation of air by injection of helium gas. A depressurization accident is one of the design-basis accidents of a Very High Temperature Reactor (VHTR). When the primary pipe rupture accident occurs in the VHTR, air is expected 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 air in the reactor pressure vessel produce continuously. In order to predict or analyze the air ingress phenomena during the depressurization accident of the VHTR, therefore, it is important to develop the method for prevention of air ingress during the accident. The experiment has been carried out regarding natural circulation using a circular tube consisting of the loop type or the reverse U-shaped type. The vertical channel consists of the one side heated tube and the other side cooled tube. The experimental results were obtained as follows. When the temperature difference between the vertical tubes was kept at 52K, the velocity of natural circulation flow became about 12cm/s. During this steady state, a small amount of helium injected to the channel. Then, the flow velocity of natural circulation suddenly decreased. The volume of injected helium is about 3% of the total volume of the channel. The velocity became around zero. After 1500 seconds elapsed, the natural circulation suddenly produced again. The experimental results show that the natural circulation flow of air can be controlled by the method of helium gas injection. This paper also discusses an overview of the method for the prevention of air ingress during the primary pipes rupture accident.

402 Study on control method of natural circulation by helium gas

2011 ◽  
Vol 2011 (0) ◽  
pp. 92-93
Author(s):  
Masashi NOMURA ◽  
Tetsuaki TAKEDA ◽  
Takuya SHIMURA
Keyword(s):  
Control Method ◽  
Natural Circulation ◽  
Helium Gas

804 Study on control method of natural circulation by injection of helium gas

2012 ◽  
Vol 2012.18 (0) ◽  
pp. 267-268
Author(s):  
Masashi NOMURA ◽  
Tetsuaki TAKEDA ◽  
Takuya SHIMURA
Keyword(s):  
Control Method ◽  
Natural Circulation ◽  
Helium Gas

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.

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