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Nonisothermal Reaction of Uranium with Water by the Condenser Discharge Method

Louis Baker, Jr.

Nuclear Science and Engineering / Volume 25 / Number 2 / Pages 116-130

June 1966

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A combined experimental and theoretical study of the reaction of solid wires and molten particles of uranium with water is reported. The experiments were performed by the condenser-discharge method that had been developed for studies of the zirconium-water reaction. The uranium-water reaction was studied with initial metal temperatures from 660 to 4000°C with 30- and 60- mil wires in water at 25°C and in water at 100°C. Wires heated to the melting point of uranium, 1133°C, reacted to a maximum of about 4% in 25°C water and 7% in 100°C water. Wires heated above the melting point formed molten particles whose mean diameter decreased continuously with increasing metal temperature. At initial metal temperatures approaching 4000°C, 45% uranium-water reaction occurred in 25°C water, and 100% reaction occurred in 100°C water. The experimental results were explained in terms of a two-step reaction scheme in which the reaction rate is initially controlled by the rate of gas-phase diffusion of water vapor toward the hot metal particles and of hydrogen, generated by reaction, away from the particles. At a later time, the reaction becomes controlled by the parabolic rate law, resulting in cooling and quenching of the reaction. Initial control of the reaction by gas-phase diffusion was shown to be responsible for the important effects of particle size and water temperature on the reaction and the relative unimportance of metal temperatures at values greater than about 1500°C. The mathematical model of the reaction of molten metal spheres with water, which was originally developed to explain the reaction of zirconium with water, was also applied to the uranium-water reaction. Good agreement between experimental and calculated extents of reaction was found for metal temperatures below the melting point using the experimental parabolic rate equation reported in the previous paper for temperatures between 600 and 1200°C. At metal temperatures above the melting point, the results were correlated with the following parabolic rate equation: V2 = 8.69 × capsules in the Tran 106 t[exp (- 30 000/RT)], where V is the volume hydrogen generated in milliliters at STP per square centimeter, t is the time in minutes, R is the gas constant in calories per mole per degree Kelvin, and T is the temperature in degrees Kelvin. The results calculated from this equation corresponded very well with the observed values. The rate equation obtained by differentiating the above equation is recommended for inclusion in reactor accident models in which the effect of uranium-water or steam reaction is to be included.

 
 
 
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