Session: 14-11 Student Paper Competition

Paper Number: 64553

Start Time: August 4, 2021, 03:00 PM

64553 - Mixing Process of Two Component Gases by Natural Convection and Molecular Diffusion 

A decompression accident due to a break in the main pipe of the primary cooling system of a gas turbine high temperature reactor 300 Cogeneration (GTHTR300C) is one of the assumed accident events at the time of design. When the main pipe of the horizontal double pipe connected to the reactor pressure vessel breaks, air enters the reactor by the counter current flow. Oxygen in the infiltrated air reacts with graphite, which is a core structure, which may damage the core shape and release fission products. When the primary cooling system main piping is connected to the lower part of the core, it is considered that stable density stratification is formed after the decompression accident. Especially in the initial stage after the accident, it is expected that the infiltration of oxygen in the air is controlled by molecular diffusion. However, when the main pipe is connected to the side of the reactor like GTHTR300C, air immediately enters the lower part of the rupture opening due to the counter current flow. After that, a stable density stratification is formed, so that the helium gas and the infiltrated air promote gas mixing by local natural convection and counter current flow in addition to molecular diffusion. Eventually, it is expected that complicated phenomena that generate natural circulation will be superimposed. In order to contribute to the improvement of safety in the event of a GTHTR300C accident, an experiment was conducted using an experimental device that simulated the flow path configuration of the reactor for the purpose of investigating the mixing process of helium and air as two component gases. The experimental equipment consisted of a coaxial double cylindrical container and a coaxial horizontal double circular tube. A ball valve is connected to the horizontal double circular tube, and a decompression accident is simulated by opening the valve. During the experiment, the gas temperature, air concentration, and gas flow velocity at each measurement point were measured. As a result, it was confirmed that a stable density stratification of air and helium was formed in the experimental equipment, and that a natural circulation flow that circled the inside of the furnace was generated after a certain period of time.

Presenting Author: Takeaki Ube Mechanical Engineering Course, Integrated Graduate School of Medicine, Engineering, and Agricultural Sciences, University of Yamanashi

Authors:

Takeaki Ube Mechanical Engineering Course, Integrated Graduate School of Medicine, Engineering, and Agricultural Sciences, University of Yamanashi
Tetsuaki Takeda Graduate School of Engineering University of Yamanashi