EXPERIMENTS ON HIGH-TEMPERATURE GRAPHITE AND STEAM REACTIONS UNDER LOSS-OF-COOLANT ACCIDENT CONDITIONS

To obtain fundamental data for safety analyses of fusion reactors with regard to loss of coolant inside the vacuum vessel, the rate of corrosion reaction between high temperature graphite and steam was measured experimentally between 1000 and 1600 degrees C. A preliminary experiment gave an activation energy for reaction between oxygen and isotropic graphite as 45 kJ mol(-1). The reaction rate with steam depended on temperature, with an inflection point near 1300 degrees C. The activation energy was about 270 kJ mol(-1) at temperatures below 1300 degrees C, and 104 kJ mol(-1) at higher temperatures. The energy was not strongly dependent on the graphite properties, but the reaction rate Varied with them. The reactivity of the isotropic graphite was more than twice as high as that of C/C composite. The molar ratio of the product gases [H-2]/[CO] increased slightly with increasing temperature. Although the [CO]/[CO2] ratio also increased with temperature to 1300 degrees C, it decreased above this temperature. This behavior reflects a change in reaction mechanism near this temperature; the composition of the product gas could be estimated numerically using elementary reaction rates.