Safety implications of a graphite oxidation accident in the Compact Ignition Tokamak device

The possible safety consequences of an air ingress accident in the Compact Ignition Tokamak (CIT) device are considered. An experimental program was undertaken to determine oxidation rates of four nuclear-grade graphites in air at temperatures ranging from 800° to 1800°C and flow velocities from 3 to 7 m/s. On the basis of these test results, an analytic model was developed to assess the extent of first wall/divertor protective tile oxidation and the amount of energy released from this oxidation. For the CIT, the air seals and walls of the surrounding test cells will provide significant restriction to vacuum vessel air inflow. Under these conditions, the graphite oxidation reaction inside the vacuum vessel will become oxygen-starved within minutes of the onset of this event. Since significant oxidation rates were not achieved, the heat release did not elevate structural temperatures to levels of concern with regard to activated material release