Volatilization of urania in steam at elevated temperatures

The volatilization rates of urania in purr steam and in mixtures of steam a nd argon, steam and helium, and in steam/Ar/H-2 were measured in a thermogr avimetric apparatus at atmospheric pressure and temperatures from 1250 degr ees C to 1600 degrees C. The objective was to clarify the kinetics and mech anism of the volatilization process and to assess the validity of existing thermodynamic data that is needed to interpret the kinetic data. The mass t ransfer characteristics of the system were determined independently by meas uring the evaporation rates of metals of well-known vapor pressures. The me asurements of urania volatilization show that the rate-controlling process is gas-phase mass transfer of uranium-bearing species such as UO3. Analysis of the volatilization data also suggests that the calculated UO3 vapor pre ssures are somewhat in error at the lower temperatures in the range tested. (C) 1999 Elsevier Science B.V. All rights reserved.