Isothermal Reaction of Uranium with Steam Between 400 and 1600°C

Isothermal studies of the kinetics of the reaction of metallic uranium with steam by a volumetric method are reported. The reaction U + 2H₂O → UO₂ + 2H₂, ∆H = -142 kcal/mole at 1133°C, could be described accurately by the following parabolic rate law between 600 and 1200°C: V² = (1.95±0.8)× 10⁵ t[exp(-18 600±750)/ RT], where V is the volume of H₂ evolved in milliliters at STP per square centimeter, t is the time in minutes, R is the gas constant, 1.987 cal/(mole deg K), and T is the absolute temperature in degrees Kelvin. Between 1200 and 1600°C the following parabolic rate law described the experimental results: V² = (1.59± 0.5) × 10⁶ t[exp(-25 000 ± 1000)/RT], although it was likely that an activation energy somewhat greater than 25 kcal/mole should be used for extrapolation to short reaction times or higher reaction temperatures. The reaction at 400°C followed a linear rate, while at 500°C the reaction was complicated by effects of the transition from a linear reaction at low temperatures to a parabolic reaction at higher temperatures. The oxide formed at 600°C and above was a glossy black UO₂ which did not flake off until the samples were cooled after exposure. Oxide formed at 400°C was a brown colloidal material that was continually washed from the sample.