4:05 PM - 4:20 PM
[3J15] Study on Air Ingress Phenomena during a Depressurization Accident of VHTR
(3)Influence of pipe rupture position on onset time of natural circulation
Keywords:Very high temperature reactor, multi-component gas, natural convection, molecular diffusion, air ingress
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. Experiments and numerical analysis using three-dimensional (3D) CFD code have been carried out to obtain the mixing process of two-component gases and the flow characteristics of localized natural convection. The results obtained from the experiments were quantitatively simulated using 3D numerical analysis. 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.