Host: The Japan Society of Mechanical Engineers
Name : The 30th International Conference on Nuclear Engineering (ICONE30)
Date : May 21, 2023 - May 26, 2023
This study concerns the safety design for depressurization accidents in very high temperature reactors (VHTRs). If the primary piping ruptures, helium gas will gush into the containment vessel. In the event of a depressurization accident, air is expected to enter the reactor core. Contact between the reactor core and the air may damage the reactor core.
During an accident, helium gas, which has a lower density than air, is passively injected into the piping. Therefore, we believed in the possibility of temporary or long-term stopping of the occurrence of natural circulation flow, in which air enters through the fracture surface. In this study, the mechanism of the cessation of natural circulation flow and resumption of natural circulation flow after helium gas injection were investigated in detail through experiments and numerical analysis using an inverted U-shaped vertical fluid layer apparatus. When considering this, local natural convection and molecular diffusion must be considered. Experiments were conducted to study the mechanism of cessation and reemergence of natural circulation flow during helium gas injection. The experimental apparatus consisted of a storage tank and an inverted U-shaped vertical slot. The temperature difference between the fluid layers generated a natural circulation flow. Numerical analysis was performed using a 3-D Computational Fluid Dynamics (CFD) code. Steady-state analysis was performed before helium gas injection, followed by unsteady-state analysis.
