Molecular Diffusion Studies in Gases at High Temperature. IV. Results and Interpretation of the CO2–O2, CH4–O2, H2–O2, CO–O2, and H2O–O2Systems

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

10.1115/icone28-64553 ◽

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.

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Dimethyl- and Bis[(trimethylsilyl)methyl]cuprates Show Aggregates Higher than Dimers in Diethyl Ether: Molecular Diffusion Studies by PFG NMR and Aggregation−Reactivity Correlations

Journal of the American Chemical Society ◽

10.1021/ja026311m ◽

2003 ◽

Vol 125 (6) ◽

pp. 1595-1601 ◽

Cited By ~ 27

Author(s):

Xiulan Xie ◽

Carsten Auel ◽

Wolfram Henze ◽

Ruth M. Gschwind

Keyword(s):

Diethyl Ether ◽

Molecular Diffusion ◽

Diffusion Studies ◽

Pfg Nmr

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Methodology Development for Transient Flow Distribution Analysis in High Temperature Gas-Cooled Reactor

Volume 2: Nuclear Policy; Nuclear Safety, Security, and Cyber Security; Operating Plant Experience; Probabilistic Risk Assessments; SMR and Advanced Reactors ◽

10.1115/icone2020-16199 ◽

2020 ◽

Author(s):

Takeshi Aoki ◽

Hiroyuki Sato ◽

Hirofumi Ohashi

Keyword(s):

High Temperature ◽

Hydraulic System ◽

System Analysis ◽

Molecular Diffusion ◽

Transient Flow ◽

Flow Distribution ◽

Distribution Analysis ◽

Design Improvement ◽

Air Ingress ◽

High Temperature Gas

Abstract In the thermal hydraulic design of the prismatic-type of the high temperature gas cooled reactor (HTGR), unintended flows such as gap flows between columns, cross flows between column layers and gap flows between permanent reflectors should be analyzed to minimizing the unintended flows. The flow distribution considering unintended flows in the reactor has been evaluated for steady and conservative condition. On the other hand, the transient thermal hydraulic analysis for satisfactorily realistic conditions will be helpful for the design improvement of prismatic-type HTGR. The present study aims to improve the thermal hydraulic system analysis code developed by Japan Atomic Energy Agency based on the RELAP5/MOD3 code and confirm its applicability for the transient flow distribution analysis for prismatic-type HTGRs during anticipated operational occurrences and accidents for its design improvement utilizing experiences on high temperature engineering test reactor (HTTR) design. The calculation model and code were developed and validated to evaluate the detailed flowrate distribution considering the unintended flows in the core and the molecular diffusion that is important to analyze beginning air ingress behavior in an air ingress accident triggered by a rupture of a primary coolant piping in HTGR. It is concluded that a prospect has confirmed to apply the improved thermal hydraulic system analysis code for transient flow distribution analysis for prismatic-type HTGRs.

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