It has been observed that in a completely austenitic stainless -steel system containing flowing sodium under a temperature gradient, carbon is transferred from high- (1300°F) to low-temperature regions (1100 °F). This mode of carbon transport cannot be explained from the temperature dependence of the activity of carbon in stainless steels. Based on simple thermodynamic calculations and analysis of electron energy levels in liquid sodium, various models of mechanism and species involved in carbon transport have been analyzed. A new model where atomic carbon (in solution in sodium) is responsible for the carbon transport in an austenitic stainless-steel system has been proposed. Furthermore, it is believed that the temperature variation of the activity of carbon in solution in sodium determines the direction of carbon movement.