Vapor pressure of plutonium carbide adsorbed on graphite

An investigation was conducted to obtain data needed to make realistic estimates of plutonium contamination in the primary coolant system in High Temperature Gas-Cooled Reactors (HTGRs). The vapor pressure of plutonium over plutonium sesquicarbide (Pu2C3) adsorbed on the surface of H-451 graphite was found to be defined by adsorption isotherms at test temperatures of 1000, 1200, and 14000C. The vapor pressures at low concentrations of Pu2C3 on the surface of the graphite were up to three orders of magnitude below that of pure Pu2C3 at a given temperature. The heat of adsorption increases with decreasing Pu2C3 surface coverage with the measured value at 0.05 μmol Pu2C3/m2 being 107.9 kcal/mol. The Pu2C3 concentration required for monolayer surface coverage on the graphite was found to be 3.27 μmol/m2