Carbon Loss from Graphite Cylinders Exposed to Steam for Short Times

The rate, extent, and spatial variation of carbon loss from a graphite cylinder exposed to steam has been calculated as a function of time. The geometrical arrangement considered was a hollow cylinder with a helium-steam mixture on the inside. At the outer boundary either a zero concentration or a zero steam flux may be maintained. The reaction was assumed to be first order. Changes in the rate of carbon removal with time other than those associated with establishing a steady-state steam concentration gradient were not considered. Calculations using constants derived from current experimental work lead one to conclude that the time needed to establish a concentration gradient is insignificant compared with the times for which the hot core of a high-temperature gas-cooled reactor could be exposed to steam accidentally. This conclusion could change if much tighter graphites or more massive sections, equivalent to thicker cylinders in our analysis, were to be used.