Fusion Science and Technology / Volume 45 / Number 4 / June 2004 / Pages 592-596
Carbon fiber composites (CFCs) are often suggested as armor material for the first wall of a fusion plasma chamber because of carbon's low atomic number, high thermal conductivity, and high melting point. However, carbon is chemically reactive in air and readily absorbs tritium. Accordingly, it is believed that during a loss-of-vacuum accident (LOVA), the CFC armor will react with the air ingress and release its absorbed tritium. The mobilization of this tritium and the carbon monoxide produced by the CFC-air chemical reaction are both safety concerns. This paper discusses the MELCOR thermal-hydraulic analysis of a simulated LOVA for the SOMBRERO fusion design. The MELCOR analysis is important because it included data from recent oxidation experiments that studied the advanced CFC NB31. A previous MELCOR analysis of a simulated SOMBRERO LOVA event suggested that the ingress of air would aggressively oxidize the CFC. While the current analysis revealed initial first-wall temperatures that exceed those of the prior analyses, the trend reversed 10 h after the onset of the LOVA. The calculated wall temperatures at the back of the blanket for the current analysis were consistently lower than those previously calculated using the older data. Accordingly, the conclusion is that a LOVA event for a fusion design similar to SOMBRERO may not be as grave as once predicted.