STUDY ON AIR INGRESS DURING AN EARLY STAGE OF A PRIMARY-PIPE RUPTURE ACCIDENT OF A HIGH-TEMPERATURE GAS-COOLED REACTOR

A primary-pipe rupture accident is one of the design-based accidents of the HTTR. As the first step of our final goal of predicting the multicomponent gas flow in a reactor during the early stages of the accident, the present paper aims at studying experimentally and analytically, the basic features of air ingress and gas transportation by transient molecular diffusion and the transient natural convection of a two-component gas mixture. The present paper comprises two main parts. The first part deals with analytical and experimental studies on N2 ingress (corresponding to air ingress) and gas transportation by molecular diffusion and the one-dimensional natural convection of an He-N2 two-component gas mixture in a reverse-U-shaped tube. Analytical and experimental results are discussed on the N2 mole fraction change with time after the simulated pipe rupture and on the initiation time of the natural circulation of pure N2. The second part deals with a preliminary simulation test of air ingress during the early stages of the accident. The test is performed with a very simple model of the reactor. The experimental results are discussed on the change in mole fraction of air with time and on the initiation time of the natural circulation of pure air.