Research and development on prevention of air ingress during the primary-pipe rupture accident in the HTTR

A primary-pipe rupture accident is one of the design-basis accidents of a high-temperature gas-cooled reactor (HTGR). When the primary-pipe rupture accident occurs, air is expected to enter the reactor core from the breach and oxidize in-core graphite structures. In order to predict or analyze the process of air ingress during the primary-pipe rupture accident of HTGRs, it is very important to develop computer programs and to validate them by experiments. This paper describes a computer program, which is named FLOWGR, developed to analyze the process of air ingress during the first stage of the primary-pipe rupture accident, in the case of the primary-pipe attached to the bottom part of the reactor core. An overview of the method is given for the prevention of air ingress into the reactor during the primary-pipe rupture accident. The numerical results are in good agreement with the experimental ones regarding the density of the gas mixture, the concentration of each gas species produced by the graphite-oxidation reaction and the onset time of the natural circulation of air. The experimental results show that the natural circulation flow of air during the accident can be controlled by the method of helium gas injection into the reactor pressure vessel