[en] Experiments on mass transfer in a natural convection of gas mixture with graphite corrosion at high temperature due to air ingress have been performed to predict the thermohydraulic characteristics with high accuracy at the pipe rupture in a high temperature gas cooled reactor. The whole shape of the multi-channel test section is a reverse U shape. The one side of the reverse U shaped test section consists of two hot graphite channels and one cold metal channel which are parallel to each other. The inlet and outlet mole fractions of oxygen, carbon monoxide and carbon dioxide, the corrosion thickness of the graphite tube, the distribution of flow rates were measured under the various temperature conditions of graphite channels up to 1200degC. From these data, the relationship of Sherwood number and dimensionless distance from the inlet of the graphite channel have been obtained. It was found under the present experimental conditions that the maximum mole fraction of carbon monoxide at the outlet is 0.25% and the Sherwood numbers obtained are smaller than those calculated on assumption of analogy between heat and mass transfer. (author)