| Abstract: | A primary-pipe rupture accident is one of the design-based accidents of a high-temperature engineering test reactor (HTTR), which is being developed at JAERI. When the primary pipe ruptures, air is expected to enter into the reactor core from the breach by molecular diffusion and natural convection. In order to investigate the process of air ingress during the early stage of the primary-pipe rupture accident, experimental and analytical studies are performed on the conjugate phenomenon of the transient molecular diffusion and natural convection of a two-component gas mixture in two test sections, a reverse-U-shaped tube and a test model simulating simply the reactor. One-dimensional basic equations for continuity and momentum conservation are numerically solved to obtain a concentration change of gas species and an initiation time of a natural circulation of pure nitrogen in the reverse-U-shaped tube. Moreover, a modified numerical solution is proposed to reduce the computing time. A one-dimensional flow net work model is employed to calculate the transport process of air in the test model simulating the reactor. The calculated results agree well with the experimental ones on the concentration change of gas species and the initiation time of the natural circulation of pure nitrogen or pure air. |
