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Research Papers

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

[+] Author and Article Information
Tetsuaki Takeda

Department of Mechanical Engineering,
Graduate School of Engineering,
University of Yamanashi,
4-3-11 Takeda,
Kofu 400-8511, Yamanashi, Japan
e-mail: ttakeda@yamanashi.ac.jp

Manuscript received November 5, 2017; final manuscript received October 5, 2018; published online March 15, 2019. Assoc. Editor: Yanping Huang.

ASME J of Nuclear Rad Sci 5(2), 021003 (Mar 15, 2019) (11 pages) Paper No: NERS-17-1288; doi: 10.1115/1.4041690 History: Received November 05, 2017; Revised October 05, 2018

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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References

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Figures

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Fig. 1

Schematic drawing of GTHTR-300C and its simple models

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Fig. 2

Schematic of apparatus consisting of reverse U-shaped passage

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Fig. 3

High-temperature side passage

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Fig. 4

Numerical model consisting of the reverse U-shaped passage and the storage tank

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Fig. 5

Mesh arrangement in the X–Z plane

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Fig. 6

Mesh arrangement in the X–Y plane

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Fig. 7

Gas temperature change in the high-temperature side passage in the experiment (He/Ar, ΔT = 100 K)

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Fig. 8

Gas temperature change in the low-temperature side passage in the experiment (He/Ar, ΔT = 100 K)

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Fig. 9

Gas temperature change in the high-temperature side passage in the numerical analysis (He/Ar, ΔT = 100 K)

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Fig. 10

Gas temperature change in the low-temperature side passage in the numerical analysis (He/Ar, ΔT = 100 K)

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Fig. 11

Flow velocity distribution obtained from the numerical analysis (He/Ar, ΔT = 100 K): (a) 30 min localized natural convection generated in the high-temperature side passage, (b) 52 min just before natural circulation generated, and (c) 54 min natural circulation generated through the passage

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Fig. 12

Gas temperature distribution obtained from the numerical analysis (He/Ar, ΔT = 100 K): (a) 30 min localized natural convection generated in the high-temperature side passage, (b) 52 min just before natural circulation generated, and (c) 54 min natural circulation generated through the passage

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Fig. 13

Molar fraction change of Ar obtained from the numerical analysis (He/Ar, ΔT = 100 K): (a) 30 min mixing by molecular diffusion was promoted by localized natural convection in the high-temperature side passage, (b) 52 min just before natural circulation generated, and (c) 54 min natural circulation generated through the passage and mole fraction became uniform

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Fig. 14

Flow velocity distribution in the top space of the high-temperature side passage (N2/Ar, ΔT = 100 K)

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Fig. 15

Molar fraction change of Ar in the N2/Ar and Ne/Ar experiments (ΔT = 50 K): (a) high-temperature side and (b) low-temperature side

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Fig. 16

Molar fraction change of Ar in the N2/Ar and Ne/Ar experiments (ΔT = 70 K): (a) high-temperature side and (b) low-temperature side

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Fig. 17

Molar fraction change of Ar in the high-temperature side passage (N2/Ar, ΔT = 30, 50, 70, 100 K)

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Fig. 18

Molar fraction change of Ar in the high-temperature side passage (Ne/Ar, ΔT = 30, 50, 70, 100 K)

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Fig. 19

Molar fraction change of N2 in the high-temperature side passage (He/N2, ΔT = 30, 50, 70, 100 K)

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Fig. 20

Molar fraction change of Ar in the high-temperature side passage (He/Ar, ΔT = 30, 50, 70, 100 K)

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Fig. 21

Onset time of natural circulation against wall temperature of the high-temperature side passage

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Fig. 22

Onset time of natural circulation against wall temperature of the high-temperature side of the reverse U-shaped passages

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Fig. 23

Re-onset time of natural circulation in the reverse U-shaped passage

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Fig. 24

Relationship between re-onset time of natural circulation and amount of injecting helium gas using simple reverse U-shaped tube

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Fig. 25

Apparatus simulated horizontal pipe rupture accident in GTHTR-300C

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